What are dermatomes. How do they relate to spinal nerves. What is the significance of the C4-5 dermatome. How are dermatomes tested clinically. Why are dermatome maps controversial.

The Fundamentals of Dermatomes: Mapping Sensory Innervation

Dermatomes play a crucial role in understanding the relationship between spinal nerves and skin sensation. The term “dermatome” combines two Greek words: “derma” (skin) and “tome” (cutting or thin segment). Essentially, a dermatome represents an area of skin innervated by sensory fibers from a specific spinal nerve root.

There are 30 dermatomes in total, corresponding to the following spinal nerve levels:

• 8 cervical nerves (C1-C8, with C1 having no dermatome)
• 12 thoracic nerves (T1-T12)
• 5 lumbar nerves (L1-L5)
• 5 sacral nerves (S1-S5)

Each dermatome relays sensation from a particular region of the skin to the brain. Understanding this distribution is essential for diagnosing and localizing various neurological conditions.

The C4-5 Dermatome: Key Features and Clinical Relevance

The C4-5 dermatome encompasses a specific area of sensory innervation. Here are the key points to understand:

• C4 dermatome: Covers the shoulder area, clavicular region, and upper scapular area
• C5 dermatome: Includes the deltoid area and the anterior aspect of the entire arm to the base of the thumb

Why is the C4-5 dermatome clinically significant? Damage or dysfunction in the C4-5 spinal nerve roots can manifest as sensory disturbances in these areas. This information is valuable for diagnosing conditions such as cervical radiculopathy or assessing the level of spinal cord injuries.

Dermatome Mapping: Historical Perspectives and Modern Challenges

The concept of dermatomes has evolved over time, with several influential maps shaping our understanding:

1. Keegan and Garret Map (1948): Aligns dermatomes with the developmental progression of limb segments
2. Foerster Map (1933): Depicts the medial upper limb innervation by T1-T3, often used in clinical settings
3. Lee et al. “Evidence-Based” Map: A recent attempt to synthesize the most credible evidence from various sources

Despite these efforts, dermatome mapping remains controversial. Why is there ongoing debate about dermatome accuracy? The primary reasons include significant variations between individuals and inconsistencies among different maps. Some researchers argue that current dermatome maps are based on flawed studies and may not accurately represent the true sensory distribution.

Clinical Applications: Dermatome Testing and Neurological Examination

How do healthcare professionals utilize dermatome knowledge in clinical practice? Dermatome testing is an integral part of the neurological examination, serving two primary purposes:

1. To determine if sensory loss in a limb corresponds to a single spinal segment, suggesting a nerve root lesion (radiculopathy)
2. To assign a neurological “level” to a spinal cord lesion

What is the proper technique for dermatome testing? The ideal method involves using both a pin and cotton wool. The patient is asked to close their eyes and provide feedback on sensations as the examiner tests different areas. This approach helps assess both light touch and pain sensations across dermatomes.

The Interplay Between Dermatomes and Peripheral Nerves

Understanding dermatomes requires recognizing their relationship with peripheral nerves. How do spinal nerve roots contribute to peripheral nerve formation? Many nerve roots intertwine in plexuses (brachial, lumbar, or lumbosacral) to form different peripheral nerves. This arrangement can result in a single nerve root supplying multiple peripheral nerves.

For example:

• The median nerve derives from C6, C7, C8, and T1 nerve roots
• The ulnar nerve originates from C7, C8, and T1 nerve roots

This complex interplay highlights the importance of comprehensive neurological assessment when diagnosing and localizing nerve-related conditions.

Dermatome Dysfunction: Recognizing and Interpreting Symptoms

When spinal nerve roots are compromised, patients may experience symptoms in the corresponding dermatome. What are the potential causes of dermatome dysfunction?

• Infection
• Compression (e.g., herniated disc, tumor)
• Traumatic injury

How do these issues manifest clinically? Patients may report altered sensation, pain, or numbness in the affected dermatome. For instance, a C5 nerve root compression might cause symptoms in the deltoid area and the outer part of the upper arm.

Recognizing these patterns is crucial for accurate diagnosis and appropriate treatment planning. Healthcare providers must correlate clinical findings with anatomical knowledge to pinpoint the source of neurological symptoms.

Beyond Sensory Function: The Broader Impact of Spinal Nerve Roots

While dermatomes primarily relate to sensory distribution, it’s essential to recognize that spinal nerve roots have broader functions. How do nerve roots contribute to motor control and reflex activity?

• Motor function: Spinal nerve roots contain efferent fibers that innervate specific muscle groups
• Reflex arcs: Nerve roots play a crucial role in mediating various reflexes, such as the knee-jerk reflex

This multifaceted nature of spinal nerve roots underscores the importance of comprehensive neurological assessment. When evaluating patients with suspected nerve root disorders, clinicians must consider sensory, motor, and reflex components to form a complete clinical picture.

Dermatomes in the Digital Age: Technological Advancements and Future Directions

How is technology shaping our understanding and application of dermatome knowledge? Recent advancements are opening new avenues for research and clinical practice:

• 3D mapping: Advanced imaging techniques allow for more precise visualization of nerve root distributions
• AI-assisted diagnosis: Machine learning algorithms are being developed to aid in interpreting complex dermatome patterns
• Virtual reality training: Medical students and residents can now practice dermatome assessment in immersive, simulated environments

What does the future hold for dermatome research? Ongoing studies aim to refine our understanding of individual variations and develop more accurate, personalized dermatome maps. These efforts could lead to improved diagnostic accuracy and more targeted treatment approaches for neurological conditions.

As our knowledge evolves, healthcare professionals must stay informed about the latest developments in dermatome research and their implications for clinical practice. This ongoing learning process ensures that patients receive the most up-to-date and evidence-based care possible.

Integrating Dermatome Knowledge in Multidisciplinary Care

The concept of dermatomes extends beyond neurology, influencing various medical specialties. How do different healthcare professionals utilize dermatome knowledge in their practice?

• Orthopedic surgeons: Guide surgical approaches and interpret post-operative sensory changes
• Pain management specialists: Target specific nerve roots for interventional procedures
• Physical therapists: Design rehabilitation programs based on affected dermatomes and associated muscle groups
• Emergency medicine physicians: Quickly assess potential spinal cord injuries or nerve root compressions

This multidisciplinary application highlights the far-reaching impact of dermatome understanding in modern healthcare. By fostering collaboration and knowledge-sharing among specialties, medical professionals can provide more comprehensive and effective patient care.

How can healthcare systems promote better integration of dermatome knowledge across disciplines? Potential strategies include:

1. Interdisciplinary training sessions
2. Shared clinical decision-making tools
3. Collaborative research initiatives

By breaking down silos and encouraging a holistic approach to neurological assessment, healthcare providers can maximize the clinical utility of dermatome knowledge.

Dermatomes and Patient Education: Empowering Through Understanding

How can healthcare providers effectively communicate dermatome concepts to patients? Educating patients about their condition using dermatome knowledge can improve treatment adherence and outcomes. Consider these approaches:

• Visual aids: Use simplified dermatome maps to illustrate affected areas
• Analogies: Compare dermatomes to “postal codes” for different body regions
• Interactive tools: Employ mobile apps or websites that allow patients to explore dermatome distributions

Why is patient education about dermatomes important? When patients understand the connection between their symptoms and specific nerve roots, they are better equipped to:

1. Recognize and report changes in their condition
2. Understand the rationale behind treatment approaches
3. Actively participate in their care and rehabilitation

By fostering this understanding, healthcare providers can empower patients to take an active role in their neurological health and recovery process.

Challenges in Dermatome Assessment: Navigating Clinical Complexities

While dermatome testing is a valuable diagnostic tool, it comes with its own set of challenges. What factors can complicate dermatome assessment?

• Individual variations: Dermatome patterns can differ significantly between patients
• Overlapping innervation: Adjacent dermatomes often have areas of sensory overlap
• Central nervous system conditions: Disorders affecting the brain or spinal cord can alter sensory perception
• Psychological factors: Patient anxiety or misunderstanding of instructions can influence test results

How can clinicians navigate these challenges to ensure accurate assessment? Consider these strategies:

1. Use multiple testing modalities (e.g., light touch, pinprick, temperature)
2. Perform bilateral comparisons to identify asymmetries
3. Correlate findings with other neurological signs and symptoms
4. Repeat assessments over time to track changes

By acknowledging these complexities and employing a thorough, systematic approach, healthcare providers can maximize the diagnostic value of dermatome testing while minimizing potential pitfalls.

The Global Perspective: Cultural and Geographical Variations in Dermatome Understanding

How does the understanding and application of dermatome knowledge vary across different cultures and healthcare systems? While the anatomical basis of dermatomes is universal, their interpretation and clinical use can be influenced by various factors:

• Traditional medicine practices: Some cultures may integrate dermatome concepts with traditional healing methods
• Healthcare resources: Access to advanced imaging and diagnostic tools can impact reliance on dermatome assessment
• Medical education: Emphasis on dermatome knowledge may vary in different educational systems
• Research focus: Some regions may prioritize dermatome studies more than others

What can the global medical community learn from these variations? By examining diverse approaches to dermatome understanding and application, healthcare professionals can:

1. Identify best practices from different healthcare systems
2. Develop more culturally sensitive diagnostic and treatment approaches
3. Foster international collaboration in dermatome research
4. Improve global standards for neurological assessment

This global perspective encourages a more inclusive and comprehensive approach to dermatome knowledge, ultimately benefiting patients worldwide.

Dermatomes in the Context of Evolving Neurological Science

As our understanding of the nervous system continues to advance, how does the concept of dermatomes fit into the broader landscape of neurological science? Consider these emerging areas of research and their potential impact on dermatome knowledge:

• Neuroplasticity: Studies on the brain’s ability to rewire itself may shed light on how dermatome patterns can change over time
• Neuromodulation: Techniques like spinal cord stimulation are exploring ways to influence sensory perception within dermatomes
• Genetics: Research into genetic factors affecting nerve development could explain individual variations in dermatome patterns
• Molecular neurobiology: Understanding the molecular basis of sensory neuron development may refine our concept of dermatomes

How might these advancements shape the future of dermatome-based diagnostics and treatments? Potential developments include:

1. More personalized dermatome maps based on genetic profiles
2. Advanced neuromodulation therapies targeting specific dermatomes
3. Improved understanding of sensory recovery patterns after nerve injuries
4. Novel diagnostic tools integrating dermatome knowledge with other neurological markers

As the field of neurology evolves, healthcare professionals must stay informed about these developments and their potential implications for clinical practice. This ongoing integration of new knowledge ensures that dermatome concepts remain relevant and valuable in the ever-advancing landscape of neurological science.

Dermatomes – Physiopedia

Original Editor – Lucinda Hampton

Top Contributors –

Naomi O’Reilly,

Anas Mohamed,

Lucinda hampton,

Joao Costa,

Nikhil Benhur Abburi,

Rachael Lowe,

Kim Jackson and

Blessed Denzel Vhudzijena

Lead Editors  

Contents

• 1 Dermatomes
• 2 History
• 3 Purpose
• 4 Technique
• 5 Controversies
• 6 Clinical Significance
• 7 References

The term “dermatome” is a combination of two Greek words; “derma” meaning “skin”, and “tome”, meaning “cutting” or “thin segment”. Dermatomes are areas of the skin whose sensory distribution is innervated by the afferent nerve fibres from the dorsal root of a specific single spinal nerve root, which is that portion of a peripheral nerve that “connects” the nerve to the spinal cord.

Nerve roots arise from each level of the spinal cord (e. g., C3, C4), and many, but not all, intermingle in a plexus (brachial, lumbar, or lumbosacral) to form different peripheral nerves as discussed above. This arrangement can result in a single nerve root supplying more than one peripheral nerve. For example, the median nerve is derived from the C6, C7, C8, and T1 Nerve Roots, whereas the ulnar nerve is derived from C7, C8, and T1.

In total there are 30 dermatomes that relay sensation from a particular region of the skin to the brain – 8 cervical nerves (note C1 has no corresponding dermatomal area), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves. Each of these spinal nerves roots.^[1] Dysfunction or damage to a spinal nerve root from infection, compression, or traumatic injury can trigger symptoms in the corresponding dermatome. ^[2]

^[3]

Table. 1 Dermatomes

Nerve Root			Dermatome
Cervical	C2	Supply Skin of Neck	Temple, Forehead, Occiput
	C3		Entire Neck, Posterior Cheek, Temporal Area, Prolongation forward under Mandible
	C4		Shoulder Area, Clavicular Area, Upper Scapular Area
	C5	Supply the Arms	Deltoid Area, Anterior aspect of entire arm to base of thumb
	C6		Anterior Arm, Radial side of hand to thumb and index finger
	C7		Lateral Arm and Forearm to index, long, and ring fingers
	C8		Medial Arm and forearm to long, ring, and little fingers
Thoracic	T1		Medial side of forearm to base of little finger
	T2	Supply the chest and abdomen	Medial side of upper arm to medial elbow, pectoral and midscapular areas
	T3 – 6		Upper Thorax
	T5 – 7		Costal Margin
	T8 – 12		Abdomen and Lumbar Region
Lumbar	L1		Back, over trochanter and groin
	L2		Back, front of thigh to knee
	L3	Supply Skin of Legs	Back, upper buttock, anterior thigh and knee, medial lower leg
	L4		Medial buttock, latera thigh, medial leg, dorsum of foot, big toe
	L5		Buttock, posterior and lateral thigh, lateral aspect of leg, dorsum of foot, medial half of sole, first, second, and third toes
Sacral	S1		Buttock, Thigh, and Leg Posterior
	S2	Supply Groin	Same as S1
	S3		Groin, medial thigh to knee
	S4		Perineum, genitals, lower sacrum
Coccygeal	The dermatome corresponding with the coccygeal nerves is located on the buttocks, in the area directly around the coccyx. [4][5]

The idea of dermatomes originated from initial efforts to associate anatomy with the physiology of sensation. Multiple definitions of dermatomes exist, and several maps are commonly employed. Although they are valuable, dermatomes vary significantly between maps and even among individuals,^[6] with some evidence suggesting that current dermatome maps are inaccurate and based on flawed studies.^[7][8]

The medical profession typically recognised two primary maps of dermatomes. Firstly, the Keegan and Garret Map (Fig.1) from 1948, which illustrates dermatomes in alignment with the developmental progression of the limb segments. Secondly, the Foerster Map from 1933, which portrays the medial area of the upper limb as being innervated by T1-T3, depicting the pain distribution from angina or myocardial infarction. This latter map is the most frequently used in healthcare and accounts for the dermatomes used in the American Spinal Cord Injury Association Impairment Scale (ASIA Scale). In recent years there have been few attempts at verifying these original dermatome maps. Lee et al conducted an in-depth review that examined the discrepancies among dermatome maps. They put forth an “evidence-based” dermatome map that combined elements of previous maps (Fig.3). Though the application of the term “evidence-based” may be somewhat questionable, their proposed map represents a systematic attempt to synthesise the most credible evidence available.^[6][7]

Testing of dermatomes is part of the neurological examination. They are primarily used to determine whether the sensory loss on a limb corresponds to a single spinal segment, implying the lesion is of that nerve root (i.e., radiculopathy), and to assign the neurologic “level” to a spinal cord lesion^[9].

Dermatome Testing is done ideally with a pin and cotton wool. Ask the patient to close their eyes and give the therapist feedback regarding the various stimuli. Testing should be done on specific dermatomes and should be compared to bilaterally.

• Light Touch Test – Light Touch Sensation – Dab a piece of cotton wool on an area of skin ^[10]
• Pinprick Test – Pain Sensation – Gently touches the skin with the pin ask the patient whether it feels sharp or blunt

During the review of systems, asking the patient to carefully describe the pattern or distribution of sensory symptoms (e.g., tingling, numbness, diminished, or absent sensation) provides the therapist with preliminary information to help guide the examination and to assist in identifying the dermatome(s) and nerve(s) involved.^[11]

Light touch dermatomes are larger than pain dermatomes. When only one or two segments are affected, testing for pain sensibility is a more sensitive method of examination than testing for light touch.^[9]

Dermatomes have a segmented distribution throughout your body. The exact dermatome pattern can actually vary from person to person. Some overlap between neighboring dermatomes may also occur. There exist some discrepancies among published dermatome maps based on the methodologies used to identify skin segment innervation.

In a clinical commentary, Downs and Laporte discuss the history of dermatome mapping, including the variations in methodologies employed, and the inconsistencies in the dermatome maps used in education and practice.^[11] [[Laporte C. Conflicting dermatome maps: educational and clinical implications. journal of orthopaedic & sports physical therapy. 2011 Jun;41(6):42^[12]7-34.]]

Dermatomes are important because they can help to assess and diagnose a variety of conditions. Neurological screening of dermatomes helps to assess patterns of sensory loss that can suggest specific spinal nerve involvement. For instance, symptoms that occur along a specific dermatome may indicate disruption or damage to a specific nerve root in the spine.

• Nerve Entrapment
• Radiculopathy
• Spinal Cord Injury
• Herpes Zoster ^[2]

1. ↑ Wikipedia Dermatome. Available from: https://en.wikipedia.org/wiki/Dermatome_(anatomy) (last accessed 23.4.2019)
2. ↑ ^2.02.1 Medical news today What and where are dermatomes? Available:https://www.medicalnewstoday.com/articles/what-are-dermatomes (accessed 25.5.2022)
3. ↑ M Roehrs. Dermatomes. Available from: https://www.youtube.com/watch?v=CYZBH6NX8wg&feature=youtu.be (last accessed 23.4.2019)
4. ↑ Medical news today What and where are dermatomes? Available:https://www.medicalnewstoday.com/articles/what-are-dermatomes (accessed 25.5.2022)
5. ↑ David J. Magee. Orthopedic Physical Assessment. 6th edition. Elsevier. 2014.
6. ↑ ^6.06.1 Apok V, Gurusinghe NT, Mitchell JD, Emsley HC. Dermatomes and dogma. Practical neurology. 2011 Apr 1;11(2):100-5.
7. ↑ ^{7.07. 1} Lee MW, McPhee RW, Stringer MD. An evidence-based approach to human dermatomes. Australasian Musculoskeletal Medicine. 2013 Jun;18(1):14-22.
8. ↑ Downs MB, Laporte C. Conflicting dermatome maps: educational and clinical implications. journal of orthopaedic & sports physical therapy. 2011 Jun;41(6):427-34.
9. ↑ ^9.09.1 Liebenson C, editor. Rehabilitation of the spine: a practitioner’s manual. Lippincott Williams & Wilkins; 2007.Available: https://www.sciencedirect.com/topics/medicine-and-dentistry/dermatome (accessed 25.5.2022)
10. ↑ Slide share. Dermatomes and myotomes. Available from: https://www.slideshare.net/TafzzSailo/special-test-for-dermatomes-and-myotomes (last accessed 23.4.2019)
11. ↑ ^11.011.1 Susan B.O’Sullivan, Thomas J. Schmitz, George D. Fulk. Physical Rehabilitation. 6th edition. F. A. Davis Company. 2014.
12. ↑ Downs MB, Laporte C. Conflicting dermatome maps: educational and clinical implications. journal of orthopaedic & sports physical therapy. 2011 Jun;41(6):427-34.

Dermatomes – Physiopedia

Original Editor – Lucinda Hampton

Top Contributors –

Naomi O’Reilly,

Anas Mohamed,

Lucinda hampton,

Joao Costa,

Nikhil Benhur Abburi,

Rachael Lowe,

Kim Jackson and

Blessed Denzel Vhudzijena

Lead Editors  

Contents

• 1 Dermatomes
• 2 History
• 3 Purpose
• 4 Technique
• 5 Controversies
• 6 Clinical Significance
• 7 References

The term “dermatome” is a combination of two Greek words; “derma” meaning “skin”, and “tome”, meaning “cutting” or “thin segment”. Dermatomes are areas of the skin whose sensory distribution is innervated by the afferent nerve fibres from the dorsal root of a specific single spinal nerve root, which is that portion of a peripheral nerve that “connects” the nerve to the spinal cord.

Nerve roots arise from each level of the spinal cord (e.g., C3, C4), and many, but not all, intermingle in a plexus (brachial, lumbar, or lumbosacral) to form different peripheral nerves as discussed above. This arrangement can result in a single nerve root supplying more than one peripheral nerve. For example, the median nerve is derived from the C6, C7, C8, and T1 Nerve Roots, whereas the ulnar nerve is derived from C7, C8, and T1.

In total there are 30 dermatomes that relay sensation from a particular region of the skin to the brain – 8 cervical nerves (note C1 has no corresponding dermatomal area), 12 thoracic nerves, 5 lumbar nerves and 5 sacral nerves. Each of these spinal nerves roots.^[1] Dysfunction or damage to a spinal nerve root from infection, compression, or traumatic injury can trigger symptoms in the corresponding dermatome. ^[2]

^[3]

Table. 1 Dermatomes

Nerve Root			Dermatome
Cervical	C2	Supply Skin of Neck	Temple, Forehead, Occiput
	C3		Entire Neck, Posterior Cheek, Temporal Area, Prolongation forward under Mandible
	C4		Shoulder Area, Clavicular Area, Upper Scapular Area
	C5	Supply the Arms	Deltoid Area, Anterior aspect of entire arm to base of thumb
	C6		Anterior Arm, Radial side of hand to thumb and index finger
	C7		Lateral Arm and Forearm to index, long, and ring fingers
	C8		Medial Arm and forearm to long, ring, and little fingers
Thoracic	T1		Medial side of forearm to base of little finger
	T2	Supply the chest and abdomen	Medial side of upper arm to medial elbow, pectoral and midscapular areas
	T3 – 6		Upper Thorax
	T5 – 7		Costal Margin
	T8 – 12		Abdomen and Lumbar Region
Lumbar	L1		Back, over trochanter and groin
	L2		Back, front of thigh to knee
	L3	Supply Skin of Legs	Back, upper buttock, anterior thigh and knee, medial lower leg
	L4		Medial buttock, latera thigh, medial leg, dorsum of foot, big toe
	L5		Buttock, posterior and lateral thigh, lateral aspect of leg, dorsum of foot, medial half of sole, first, second, and third toes
Sacral	S1		Buttock, Thigh, and Leg Posterior
	S2	Supply Groin	Same as S1
	S3		Groin, medial thigh to knee
	S4		Perineum, genitals, lower sacrum
Coccygeal	The dermatome corresponding with the coccygeal nerves is located on the buttocks, in the area directly around the coccyx. [4][5]

The idea of dermatomes originated from initial efforts to associate anatomy with the physiology of sensation. Multiple definitions of dermatomes exist, and several maps are commonly employed. Although they are valuable, dermatomes vary significantly between maps and even among individuals,^[6] with some evidence suggesting that current dermatome maps are inaccurate and based on flawed studies.^[7][8]

The medical profession typically recognised two primary maps of dermatomes. Firstly, the Keegan and Garret Map (Fig.1) from 1948, which illustrates dermatomes in alignment with the developmental progression of the limb segments. Secondly, the Foerster Map from 1933, which portrays the medial area of the upper limb as being innervated by T1-T3, depicting the pain distribution from angina or myocardial infarction. This latter map is the most frequently used in healthcare and accounts for the dermatomes used in the American Spinal Cord Injury Association Impairment Scale (ASIA Scale). In recent years there have been few attempts at verifying these original dermatome maps. Lee et al conducted an in-depth review that examined the discrepancies among dermatome maps. They put forth an “evidence-based” dermatome map that combined elements of previous maps (Fig.3). Though the application of the term “evidence-based” may be somewhat questionable, their proposed map represents a systematic attempt to synthesise the most credible evidence available.^[6][7]

Testing of dermatomes is part of the neurological examination. They are primarily used to determine whether the sensory loss on a limb corresponds to a single spinal segment, implying the lesion is of that nerve root (i.e., radiculopathy), and to assign the neurologic “level” to a spinal cord lesion^[9].

Dermatome Testing is done ideally with a pin and cotton wool. Ask the patient to close their eyes and give the therapist feedback regarding the various stimuli. Testing should be done on specific dermatomes and should be compared to bilaterally.

• Light Touch Test – Light Touch Sensation – Dab a piece of cotton wool on an area of skin ^[10]
• Pinprick Test – Pain Sensation – Gently touches the skin with the pin ask the patient whether it feels sharp or blunt

During the review of systems, asking the patient to carefully describe the pattern or distribution of sensory symptoms (e.g., tingling, numbness, diminished, or absent sensation) provides the therapist with preliminary information to help guide the examination and to assist in identifying the dermatome(s) and nerve(s) involved.^[11]

Light touch dermatomes are larger than pain dermatomes. When only one or two segments are affected, testing for pain sensibility is a more sensitive method of examination than testing for light touch.^[9]

Dermatomes have a segmented distribution throughout your body. The exact dermatome pattern can actually vary from person to person. Some overlap between neighboring dermatomes may also occur. There exist some discrepancies among published dermatome maps based on the methodologies used to identify skin segment innervation.

In a clinical commentary, Downs and Laporte discuss the history of dermatome mapping, including the variations in methodologies employed, and the inconsistencies in the dermatome maps used in education and practice.^[11] [[Laporte C. Conflicting dermatome maps: educational and clinical implications. journal of orthopaedic & sports physical therapy. 2011 Jun;41(6):42^[12]7-34.]]

Dermatomes are important because they can help to assess and diagnose a variety of conditions. Neurological screening of dermatomes helps to assess patterns of sensory loss that can suggest specific spinal nerve involvement. For instance, symptoms that occur along a specific dermatome may indicate disruption or damage to a specific nerve root in the spine.

• Nerve Entrapment
• Radiculopathy
• Spinal Cord Injury
• Herpes Zoster ^[2]

1. ↑ Wikipedia Dermatome. Available from: https://en.wikipedia.org/wiki/Dermatome_(anatomy) (last accessed 23.4.2019)
2. ↑ ^2.02.1 Medical news today What and where are dermatomes? Available:https://www.medicalnewstoday.com/articles/what-are-dermatomes (accessed 25.5.2022)
3. ↑ M Roehrs. Dermatomes. Available from: https://www.youtube.com/watch?v=CYZBH6NX8wg&feature=youtu.be (last accessed 23.4.2019)
4. ↑ Medical news today What and where are dermatomes? Available:https://www.medicalnewstoday.com/articles/what-are-dermatomes (accessed 25.5.2022)
5. ↑ David J. Magee. Orthopedic Physical Assessment. 6th edition. Elsevier. 2014.
6. ↑ ^6.06.1 Apok V, Gurusinghe NT, Mitchell JD, Emsley HC. Dermatomes and dogma. Practical neurology. 2011 Apr 1;11(2):100-5.
7. ↑ ^{7.07. 1} Lee MW, McPhee RW, Stringer MD. An evidence-based approach to human dermatomes. Australasian Musculoskeletal Medicine. 2013 Jun;18(1):14-22.
8. ↑ Downs MB, Laporte C. Conflicting dermatome maps: educational and clinical implications. journal of orthopaedic & sports physical therapy. 2011 Jun;41(6):427-34.
9. ↑ ^9.09.1 Liebenson C, editor. Rehabilitation of the spine: a practitioner’s manual. Lippincott Williams & Wilkins; 2007.Available: https://www.sciencedirect.com/topics/medicine-and-dentistry/dermatome (accessed 25.5.2022)
10. ↑ Slide share. Dermatomes and myotomes. Available from: https://www.slideshare.net/TafzzSailo/special-test-for-dermatomes-and-myotomes (last accessed 23.4.2019)
11. ↑ ^11.011.1 Susan B.O’Sullivan, Thomas J. Schmitz, George D. Fulk. Physical Rehabilitation. 6th edition. F. A. Davis Company. 2014.
12. ↑ Downs MB, Laporte C. Conflicting dermatome maps: educational and clinical implications. journal of orthopaedic & sports physical therapy. 2011 Jun;41(6):427-34.

Classification of the level and severity of spinal cord injury

Medical rehabilitation

Until the early 1990s, there was no single generally accepted classification of the level and severity of spinal cord injury. Doctors often used different definitions of the level of injury, complete and incomplete injuries. This article provides a classification developed by the American Spinal Injury Association (ASIA).

The spinal cord is located inside the spinal canal. Segmental levels of the spinal cord are determined by the anterior and posterior spinal roots, which connect to the spinal nerves near the intervertebral foramina. There are 8 cervical, 12 thoracic, 5 lumbar, 5 sacral and 1-3 coccygeal segments of the spinal cord (Figure 1) . The upper cervical segments are located at the level of the bodies of the cervical vertebrae corresponding to their serial number. The lower cervical and upper thoracic segments are one vertebra higher than the corresponding vertebral bodies. In the middle thoracic region, this difference is equal to two vertebrae, in the lower thoracic region, to three vertebrae. The lumbar segments are located at the level of the bodies of the tenth and eleventh thoracic vertebrae, the sacral and coccygeal segments correspond to the levels of the twelfth thoracic and first lumbar vertebrae. The lower border of the spinal cord tapering in the form of a cone is located at the level of the second lumbar vertebra. Below this level is the terminal filament, which is the remnant of the final section of the embryonic spinal cord and is surrounded by the roots of the spinal nerves and the membranes of the spinal cord. The roots of the spinal nerves at this level form the so-called cauda equina.

Figure 1. Spine and segmentation of the spinal cord

Sensory and motor levels

A dermatome is a skin area innervated by a certain segment of the spinal cord. Figures 2 and 3 show dermatomes and key points for their definition, as well as muscle groups recommended for testing by the American Spinal Injury Association. After injury, dermatomes may expand or contract due to spinal cord plasticity. The complete form that ASIA recommends filling out when examining a patient with a spinal cord injury is available in English in pdf format (Adobe Acrobat Reader required to view).

Figure 2. Areas of sensitive innervation

C2-C4. C2 dermatome includes the skin of the occiput and upper neck. C3 – lower neck and collarbone. C4 – subclavian region.
C5-T1. These dermatomes are located on the arms. C5 – outer surface of the arm at and above the elbow. C6 – radial (from the side of the thumb) part of the forearm and hand. C7 – middle finger, C8 – lateral part of the hand, T1 – inner side of the forearm.
T2-T12. Thoracic dermatomes are located in the axillary and thoracic region. T3-T12 cover chest and back to hips. The nipples are located in the middle of T4. T10 is located near the navel. T12 ends just above the thigh.
L1-L5. Dermatomes located in the area of ​​the hip joints and groin are innervated by the L1 segment of the spinal cord. L2 and L3 cover the front of the thighs and knees. L4 and L5 – medial (inner) and lateral (outer) parts of the legs.
S1-S5. S1 is located on the heel and calf. S2 – back of the thighs and popliteal fossa. S3 – medial buttocks and S4-S5 – perineum. S5 – anal area.

Figure 3. Key muscle groups

Ten muscle groups reflect the motor innervation of the cervical and lumbosacral sections of the spinal cord. The ASIA system does not test the abdominal muscles (i.e., T2-11), since at the thoracic level it is much easier to locate the affected segment of the spinal cord along the corresponding dermatome. Some other muscles (such as the popliteal) are also excluded, since the segments that innervate them are already represented by other muscles.
Muscles of the hand. C5 innervates the flexors of the forearm (biceps), C6 the extensors of the wrist, C7 the extensors of the forearm (triceps), C8 the flexors of the fingers, and T1 the abductor (adductor) of the little finger.
Leg muscles. Innervated by the lumbar segments of the spinal cord. L2 innervates the hip flexors (m. psoas), L3 – knee extensors (m. quadriceps), L4 – dorsal foot flexors (m. tibialis anterior), L5 – thumb extensors (m. extensor hallucis longus), S1 – plantar flexors of the foot (m. gastrocnemius).
The anal sphincter is innervated by S4-S5. It is very important in the neurological examination of patients with spinal cord injury. If voluntary contraction of the anal sphincter is possible, the spinal cord injury is considered incomplete, regardless of any other evidence. It is important to note that testing certain muscle groups according to the ASIA classification simplifies the real situation, since almost every muscle receives innervation from two or more segments of the spinal cord.

Levels of spinal cord injury

Doctors use two different definitions of the level of spinal cord injury. Based on the same neurological examination, neuropathologists and rehabilitation specialists can determine a different level of injury. Neuropathologists usually determine the level of damage by the first segment of the spinal cord in which dysfunction is detected. At the same time, physiotherapy and rehabilitation doctors determine the level of damage in the lowest segment with preserved function. Thus, if a patient has normal sensitivity at the C3 level and none with C4, the rehabilitator will say that the sensory level is C3, and the neuropathologist or neurosurgeon will call the damage level C4. Most traumatologists and orthopedists determine the level of damage by the level of damage to the spine.
ASIA recommends determining the level of damage by the lowest segment with preserved function.

Complete or partial damage

In the clinic, spinal cord injury is usually described as complete or incomplete. A complete injury is one in which there is no motor or sensory function below the site of injury. However, this definition is not always applicable. The following three examples illustrate the shortcomings and ambiguities of the traditional definition. The ASIA committee considered these issues when developing the spinal cord injury classification in 1992 year.

• Partially protected zones. Often, some segments of the spinal cord below the injury site retain a partial function, although in the other underlying segments, both motor and sensory function are absent. This is a fairly common occurrence. Many patients have areas of partial preservation. What kind of damage in this case – complete or incomplete, and at what level?
• Lateral preservation. A function may be partially retained on one side, but not present on the other, or be there on another level. For example, if a patient has no sensitivity with C4 on the right and with T1 on the left, is this damage complete or incomplete, and at what level?
• Restore function. An initially missing function below the fault can then be restored. Does this mean that the spinal cord injury was complete and became incomplete? This is not a trivial matter, because if, for example, a clinical trial is being conducted in which only patients with complete spinal cord injury participate, it is necessary to stipulate the timing of the assessment of the status.

Most clinicians consider damage complete if there is a level of the spinal cord below which no function is detected. The Committee of the American Spinal Injury Association decided to take this criterion to its logical limit: the injury is considered complete if there is no motor and sensory function in the anal and perineal regions, which are innervated by the sacral (S4-S5) spinal cord.
The decision to make the absence of function at the S4-S5 level the criterion for complete damage not only removed the issue of zones of partial and lateral function preservation, but also solved the problem of restoration of function. As it turned out, only in a small number of patients in whom neurological functions at the level of S4-S5 were absent, they are restored spontaneously. The ASIA classification separately indicates the motor and sensory levels on each side and the zones of partial preservation, as this simplifies the criterion for assessing the completeness of the damage.
Finally, the question itself: complete damage or incomplete, can be debatable. The absence of motor and sensory function below the injury site does not necessarily mean the absence of axons that cross the injury site. Animal studies and clinical data indicate that the function that is absent below the site of injury can be restored to some extent by restoring the blood supply to the spinal cord (in the case of arteriovenous malformation caused by ischemia), decompression (if there is chronic compression – compression of the spinal cord) or drug therapy, for example, 4-aminopyridine. Assessing spinal cord injury as complete, one should not deprive a person of hope for recovery.

Severity classification of spinal cord injury

Physicians have long used the clinical neurological deficit score, developed at Stokes Manville before World War II and introduced by Frankel in the 1970s. On this scale, patients were divided into five categories: no function (A), only sensory function (B), some sensory and motor function preserved (C), useful motor function (D), and normal (E).

ASIA Injury Severity Scale

A=Complete: No motor or sensory function in the sacral segments S4-S5
B=Incomplete: Sensation preserved but no motor function in segments below the neurological level, including S4-S5.
C=Incomplete: Motor function below the neurological level is preserved, but more than half of the key muscles are below
neurological level have a strength of less than 3 points.
D=Incomplete: Below neurological level of motor function is preserved, and at least half of the key muscles below the neurological level have a strength of 3 points or more.
E=Normal: motor and sensory functions are normal.

Clinical syndromes

Central
Brown-Sekara
Front pillars
Brain cone
Horse tail

The ASIA Spinal Cord Injury Severity Scale is based on the Frankel scale, but differs from it in a number of important ways.
First, the absence of any function below the level of damage was replaced in category A with the absence of motor and sensory function in the sacral segments S4-S5. This definition is clear and unambiguous.
Category B ASIA is essentially identical to Frankel B, but adds a requirement for retained sensory function in S4-S5. It should be noted that the defining moment in categories A and B on the ASIA scale is the preservation of motor and sensory function in S4-S5.
ASIA also added a quantitative measure for categories C and D. The Frankel scale required clinicians to rate the functional fitness of the lower extremities. This not only introduced a subjective element into the classification, but also ignored the assessment of hand function in patients with cervical spinal cord injury. To circumvent this problem, ASIA specifies that category C includes patients with more than half of the key (recommended for testing) muscles retaining strength less than 3 points. Otherwise, the patient is assigned to category D.
Category E is interesting in that it includes patients with spinal cord injury without any neurological deficit, at least detectable on neurological examination. The ASIA Motor and Sensory Scale does not take into account the presence of spasticity, pain, muscle weakness, and some forms of dysesthesia that may result from spinal cord injury. Such patients should be assigned to category E.
ASIA has also classified incomplete spinal cord injury into five types.
Central syndrome (with greater damage to the gray matter of the spinal cord – hemorrhages, necrosis): unequal severity of motor disorders in the upper and lower extremities, a varied degree of sensitivity impairment.
Brown-Sequard syndrome – damage to one half of the spinal cord: impaired motor functions and proprioceptive sensitivity on the side of the lesion and loss of pain and temperature sensitivity on the other side.
Syndrome of the anterior pillars: impaired motor functions of both pain and temperature sensitivity while maintaining proprioceptive sensitivity (damage affects the lateral corticospinal and corticothalamic tracts, the posterior columns remain intact).
Syndromes of the conus medullary and cauda equina are observed when there is damage in the region of the cone of the spinal cord and cauda equina. In this case, the spinal nerves are injured, which is manifested by flaccid paralysis of the lower extremities, anesthesia of the sciatic zone, impaired bowel and bladder functions.

Conclusion

There is no unity in terminology related to the level and severity of spinal cord injury. The American Spinal Injury Association has attempted to standardize the terms used to describe spinal cord injury. The new ASIA classification is now accepted by almost all organizations dealing with this problem worldwide.

3 facts about radicular syndrome

Many students and therapists have learned that radicular pain and radiculopathy have a dermatomal distribution. But is it really so?

First of all, let’s make a distinction between radicular pain and radiculopathy. Although “radicular pain” and “radiculopathy” are used synonymously in the literature, they are not the same. Radicular pain is defined as “pain caused by ectopic discharges emanating from the spinal root or its ganglion.” It is a neuropathic, electrical pain that travels down the leg.

Radiculopathy is another, separate concept. This is a neurological condition in which conduction along the spinal nerve or its roots is blocked (Bogduk, 2009). This results in neurological symptoms such as loss of sensation, called severe hypoesthesia or anesthesia, loss of movement, called severe paresis or atrophy, or decreased reflexes, called hyporeflexia or areflexia, if they are completely absent. If radicular pain, radiculopathy, or both are present, we speak of radicular syndrome, which is a collective term.

Is radicular pain dermatomal?

So now let’s see if radicular pain fits the dermatomal pattern. Murphy’s (2009) study observed pain patterns in patients with radicular pain and found that radicular pain in the cervical spine was accompanied by a dermatomal distribution in only 30% of cases, while it was slightly better in the lumbar spine at 36%. Now let’s look at specific dermatomes separately.

For the cervical level, only C4 seems more or less reliable (60%) – although we must be careful with interpretation, as there were only 2 patients with nerve root involvement at the C4 level. All other levels do not seem reliable. The same goes for the lumbar spine.

It appears that only the S1 level can be more or less reliable, as 65% of patients with S1 nerve root compression report pain in the dermatomal distribution of S1. All other levels did not correspond to the dermatomal distribution. However, it should be noted that Murphy and colleagues included patients with multilevel disease, which likely reduced the reliability slightly. In another more recent study by McAnany (2019) observed pain patterns in cervical radiculopathy. They found that only 54% matched the usual dermatome pattern as described in Netter’s anatomy book. With a non-standard distribution, dermatomal levels differed from the standard by 1.68 levels either cranially or caudally.

How reliable are dermatomes, myotomes and reflexes?

So if radicular pain is basically defined as shooting, electrical pain throughout the distribution of the arm or leg – how reliable are our dermatomes, myotomes and reflexes? Rainville (2017) compared sensory changes and weakness in patients with C6 and C7 radiculopathy. The scientists concluded that these symptoms are of limited value in differentiating between the two levels. Al Nezari (2013) conducted a meta-analysis to see if examination of the peripheral nervous system could diagnose the level of lumbar disc herniation. They state that sensory, motor, and reflex tests have low sensitivity, moderate specificity, and limited diagnostic accuracy for determining the level of disc herniation. Thus, while a neurologic examination can help confirm the presence of radicular syndrome and assess hypofunction to establish baseline and monitor treatment progress, it cannot determine the level of nerve root compression.

Why are our dermatome maps so unreliable?

First, there is tremendous variability in the brachial and lumbosacral plexuses. If we look at cadaveric studies of the brachial plexus, the typical anatomy of the brachial plexus was found in only 37-77% of cases. Two major variations have been described in the brachial plexus:

• We speak of “prefixation” when the C4 nerve root contributes significantly to the plexus and Th2 does not or only minimally. This variation has a prevalence between 26-48%.
• The second option is called “postfix”. This occurs if the contribution of C5 is insignificant or absent, and the innervation of Th3 is significant. This variation is present in 4% of the population. Prefixation or postfixation may change the observed pattern of cervical radiculopathy in the cranial or caudal direction, depending on the anatomical variant.

The second reason is that intradural root connections in more than 50% of cadavers are found in C5 and C6 and C6 and C7. This connection between the roots of different nerve roots is called anastomosis.

Third, the textbooks commonly used in medical programs contain numerous, conflicting maps of dermatomes. In addition, the fundamental foundations on which dermatomal maps have been created are imperfect in various respects. For example, the map created by Garrett and Keegan in 1948 has not yet been verified by subsequent research, but this map is mainly used in textbooks.

Lee et al. (2008) evaluated the literature and created a combined map of dermatomes based on published data from 5 studies that they considered the most experimentally reliable. Their map looks like this (which may be slightly different from what you and we learned in school).