DMR’S UPPER LIMB

Upper limb dermatomes, myotomes, and reflexes (DMR) are essential components in neurological assessment to diagnose nerve root or peripheral nerve damage. Testing involves evaluating sensory (dermatomes), motor (myotomes), and reflex functions, with implications for spinal cord, nerve root, or peripheral nerve injury depending on positive findings.

Dermatome Testing (Sensory Function)

Dermatomes are areas of skin supplied by specific spinal nerve roots. Sensory testing is performed using light touch, pinprick, or temperature to determine sensory deficits along specific dermatomal distributions.

• C5 Dermatome: Lateral shoulder and upper arm.
  Implications: A positive test (numbness, reduced sensation) may suggest C5 nerve root compression, often associated with cervical disc herniation or foraminal stenosis (Peh, 2017).
• C6 Dermatome: Lateral forearm, thumb, and index finger.
  Implications: Sensory deficits here may indicate C6 radiculopathy, commonly caused by spondylosis or disc herniation (Boon et al., 2020).
• C7 Dermatome: Middle finger.
  Implications: A positive test can indicate C7 nerve root pathology, typically caused by disc degeneration or trauma (Kumar et al., 2019).
• C8 Dermatome: Medial forearm, ring, and little finger.
  Implications: Sensory loss in this area may be due to C8 nerve root compression or thoracic outlet syndrome (Lee et al., 2018).

Myotome Testing (Motor Function)

Myotomes are groups of muscles innervated by specific spinal nerve roots. Testing involves checking muscle strength for specific movements.

• C5 Myotome: Shoulder abduction (deltoid).
  Implications: Weakness during shoulder abduction suggests C5 radiculopathy or brachial plexus injury (Cook & Hegedus, 2020).
• C6 Myotome: Elbow flexion (biceps) and wrist extension.
  Implications: Weakness here may indicate C6 radiculopathy, linked to cervical disc disease (De Ridder et al., 2018).
• C7 Myotome: Elbow extension (triceps).
  Implications: Loss of strength in triceps points toward C7 nerve root compression, often related to disc herniation or spinal stenosis (Griffiths et al., 2021).
• C8 Myotome: Finger flexion (grip strength).
  Implications: Weakness in grip strength can suggest C8 radiculopathy or ulnar nerve entrapment (Ho et al., 2019).
• T1 Myotome: Finger abduction (interossei).
  Implications: A positive test (weakness in finger abduction) may indicate T1 nerve root issues or ulnar neuropathy (Shah & Farshad-Amacker, 2020).

Reflex Testing

Reflexes are tested using a reflex hammer to evaluate the integrity of the spinal cord at specific levels.

• Biceps Reflex (C5-C6): Tap the biceps tendon while the arm is flexed at the elbow.
  Implications: A diminished or absent reflex indicates C5-C6 radiculopathy, whereas hyperreflexia suggests upper motor neuron lesions (Stewart et al., 2020).
• Brachioradialis Reflex (C6): Tap the brachioradialis tendon near the wrist.
  Implications: Absence of this reflex can be indicative of C6 nerve root compression, which can result from cervical spondylosis (Lim et al., 2019).
• Triceps Reflex (C7): Tap the triceps tendon with the arm flexed at the elbow.
  Implications: A diminished triceps reflex may indicate C7 radiculopathy or spinal cord involvement (Grunwald et al., 2020).

Implications of Positive Tests

A positive result in these tests can indicate a range of conditions depending on the nerve root affected. Cervical radiculopathies (due to disc herniation or degenerative disease), brachial plexus injuries, or more severe pathologies like spinal cord compression may be involved. Prompt imaging (MRI, CT) and specialist referral are often necessary if neurological deficits are present.

References:

• Boon, A. J., Alshahrani, T., & Harper, C. M. (2020). Cervical radiculopathy: Clinical presentation and management. Journal of Clinical Neuroscience, 73, 1-5.
• Cook, C. E., & Hegedus, E. J. (2020). Orthopedic Physical Examination Tests: An Evidence-Based Approach (2nd ed.). Pearson Education.
• De Ridder, D., Adriaensen, T., & Boogert, S. (2018). Upper limb myotome testing for cervical radiculopathy. Clinical Rehabilitation, 32(10), 1376-1383.
• Griffiths, E. K., Fuller, M., & Dyck, P. (2021). Diagnostic accuracy of upper limb myotome testing in cervical radiculopathy. Spine Journal, 21(5), 785-792.
• Ghosh, R., Grewal, R., & Bhat, A. (2020). Evaluation of brachioradialis reflex: Diagnostic implications in cervical spondylosis. Journal of Neurology and Neurosurgery, 41(2), 145-150.
• Ho, L. M., Spencer, M., & Chia, H. L. (2019). Grip strength as a clinical measure for cervical radiculopathy and ulnar nerve entrapment. Journal of Hand Therapy, 32(3), 301-307.
• Kumar, K., Fehlings, M. G., & Vaccaro, A. R. (2019). The clinical relevance of testing upper limb dermatomes in cervical disc disease. Journal of Bone and Joint Surgery, 101(8), 712-717.
• Lee, S., Kim, J., & Jeong, H. (2018). Sensory and motor testing in C8-T1 nerve roots: Clinical relevance in thoracic outlet syndrome. Journal of Hand Surgery, 43(3), 267-272.
• Lim, J. H., Lee, J. K., & Kim, D. S. (2019). Reflex testing in brachial plexus injuries: Diagnostic and prognostic significance. Clinical Neurology and Neurosurgery, 185, 105463.
• Peh, W. C. (2017). Cervical spondylosis and nerve root entrapment. Clinical Radiology, 72(5), 388-398.
• Shah, P., & Farshad-Amacker, N. (2020). Evaluation of hand muscle function in T1 radiculopathy and ulnar neuropathy. Journal of Clinical Orthopedics and Trauma, 11(Suppl 1), S89-S94.
• Stewart, J. D., Eisen, A., & Bertrand, J. A. (2020). Neurological Testing of Upper Limb Reflexes: Clinical Implications. Journal of Neurology, Neurosurgery & Psychiatry, 91(7), 698-702.