myosesh Myotherapy,Others Why do we perform myotome, dermatome and reflexes?

Why do we perform myotome, dermatome and reflexes?

These tests are used to see if there is any potential disc damage, PNS or CNS lesion.

Myotome muscle strength innervated by specific nerve root. This can be used to see which nerve roots are affected.


C4Shoulder elevation (shrug)
C5Shoulder abduction
C6Elbow flexion, wrist extension
C7Elbow extension, wrist flexion
C8Finger flexion
T1Finger abduction
L2Hip flexion
L3Knee extension
L4Dorsi flexion
L5Great toe extension
S1Plantar flexion
      Scale      Presentation
0No muscle contraction
1Visible or palpable muscle contraction
2Active or passive movement against decreased gravity
3Active movement against gravity
4Active movement against some resistance
5Active movement against normal resistance

Dermatome is the specific area of skin where it is innervated by specific nerve root.

Nerve root dermatome

Peripheral nerve dermatome

Light touch and pinprick

To check dermatome, soft touch with a cotton ball or tissue can be used. Crude touch is assessed by something sharp such as a pin and toothpick.

Spinothalamic tract, crossing at spinal cord, is responsible for light touch while crude and firm pressure goes through distal column medial lemniscal pathway (DCML) where it decussates at the medulla. Therefore, a patient with disc herniation affecting C7 nerve root, sensory change will be detected by soft and crude touch unilaterally at middle and ring fingers.

However, if a patient has a CNS damage, presentation might be sensory change with soft touch on right side and sensation change with pin prick on left side since the pathway crosses at different level. Thus, ALWAYS make sure to test both sides to compare.

Reflex (1, 2)

0Absent: LMN lesion sign
1Small and reduced but present reflex: may or may not be normal (may be a LMN sign)
2Brisk response: normal
3A very brisk response (hyperreflexia): may or may not be normal (May be a UMN sign)
4Hyperreflexia with clonus: abnormal (UMN lesion sign)

There are mainly 5 reflexes

· Biceps: Nerve root C5-C6

· Brachioradialis: Nerve root C6

· Triceps: C7 nerve root

· Patella: C3-C4 nerve root

· Achilles L5-S1 nerve root   

UMN lesion (damage in brain, brainstem or spinal cord) (3)

UMN lesion/damage occurs anywhere between brain to spinal cord (UMN or CNS).

Aetiology of UML lesion


·Spinal cord injury (SCI)

·Multiple sclerosis (MS)

·Cerebral palsy


Common presentations are

· Spasticity

· Hyperreflexia

· Clonus

· Positive Babinski sign

· Positive Hoffman’s sign

· Bilaterally innervated movement (jaw, eyes, face, tongue, larynx)

· Pyramidal pattern weakness (weak extensors in upper extremity and weak flexor in lower limb)

LMN lesion (nerve root, anterior horn of spinal cord)

LMN damage occurs anywhere from anterior horn, nerve root and motor axon.

Aetiology of LMN damage (4,5)

·Diabetes mellitus


·Peripheral neuropathy

·vitamin/electrode deficiencies

·Motor neuron disease

·Chronic inflammatory demyelinating polyneuropathy

·Gulliain-barre syndrome

·Myasthenia Gravis

·Cauda equina

Common presentation

· Muscle weakness and wasting (muscle innervated by nerve root)

· Hyporeflexia

· Paralysis

Clinical findings

*Absence of Achilles tendon reflex may manifest peripheral neuropathy in elderly patients (sensitivity 72.1% and specificity 90.6%) (6).

*Absent patella reflex with sensory change may indicate radiculopathy other than L3-L4 nerve root damage (L5 monoradiculopathy) (7).

*To differentiate C7 radiculopathy and radial neuropathy, C7 radiculopathy may show weakness in wrist flexion, sensory change in middle finger, triceps reflex and positive spurling test whereas radial neuropathy presents weakness in wrist extension, sensory change in thumb and absent or decreased brachioradialis reflex (8).


1, Walker, K. H. (1990). Clinical Methods: The History, Physical, and Laboratory Examinations. (3rd ed., Vol. 3). Butterworths.

2, Rodriguez-Beato, F. Y., & Jesus, O. (2020). Physiology, Deep Tendon Reflexes. Statperals, 0.

3, Emos, M. C., & Rosner, J. (2020). Neuroanatomy, Upper Motor Nerve Signs. StatPearls, 0.

4,  Figliuzzi, A., Alvarez, R., & Al-Dhahir, M. A. (2021). Achilles reflex. StatPerals, 0.

5, Garg, N., Park, S. B., Vucic, S., Yiannikas, C., Spies, J., Howells, J., Huynh, W., Matamala, J. M., Krishnan, A. V., Pollard, J. D., Cornblath, D. R., Reilly, M. M., & Kiernan, M. C. (2016). Differentiating lower motor neuron syndromes. Journal of Neurology, Neurosurgery & Psychiatry, 88(6), 474–483.

6, Richardson, J. K. (2002). The clinical identification of peripheral neuropathy among older persons. Archives of Physical Medicine and Rehabilitation, 83(11), 1553–1558.

7, Ginanneschi, F. (2015). Pathophysiology of knee jerk reflex abnormalities in L5 root injury. Functional Neurology, 187–191.

8, Robblee, J., & Katzberg, H. (2016). Distinguishing Radiculopathies from Mononeuropathies. Frontiers in Neurology, 7, 111.