What is included in a motor exam for electrodiagnostic medicine?

Updated: Aug 06, 2019
  • Author: Brian M Kelly, DO; Chief Editor: Stephen Kishner, MD, MHA  more...
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Assess muscle bulk and tone, strength, and coordination, as well as any involuntary movements, such as fasciculations or tremors. Pay attention not only to initial strength but also to endurance and fatigue, which may indicate potential neuromuscular junction disorders. [11]

The techniques involved in manual muscle testing also are quite important.

  • The clinician needs to be aware of the importance of testing of general movements of joints (such as elbow flexion, which includes 3 muscles [biceps brachii, brachialis, brachioradialis]) versus specifically testing single muscles. For example:

    • To test the biceps specifically rather than the brachialis or brachioradialis, the clinician would test supination, not elbow flexion. Controlling for other muscles is often helpful.

    • The finding of isolated abductor pollicis brevis (APB) weakness can be supportive of a median neuropathy at the wrist (CTS). [12, 13] Testing of the APB, however, can be tricky. If the thumb is not positioned properly to control for the combined vector forces of the extensor pollicis longus and flexor pollicis longus, weakness in the APB can be missed. See the image below.

      The hands of an 80-year-old woman with a several-y The hands of an 80-year-old woman with a several-year history of numbness and weakness are shown in this photo. Note severe thenar muscle (abductor pollicis brevis, opponens pollicis) wasting of the right hand, with preservation of hypothenar eminence.

A complete description of how to perform manual muscle tests of various muscles is beyond the scope of this article, but that information can be found in basic texts of physical examination, such as Hoppenfeld's Physical Examination of the Spine and Extremities. [1]

Patterns of weakness or tenderness also can suggest primary muscle disease, such as that seen in various myopathies.

Assess also various reflexes, including the monosynaptic muscle stretch reflexes, such as the patellar or Achilles reflex, and the polysynaptic superficial reflexes, such as the plantar, cremasteric, or abdominal reflex. See the lists of typical reflexes (below).

An underlying knowledge of neuromuscular anatomy is essential to examine a patient usefully, which is nowhere more apparent than in patients with brachial or lumbosacral plexopathies. [3, 15] Knowing which muscles are supplied by which roots (myotomes), cords, trunks, divisions, and peripheral nerves, as well as the sensory pattern of root dermatomes contrasted against the peripheral nerve patterns, is a must. Many laboratories have a chart available.

When symptoms dictate, evaluate for scapular winging, because the pattern of winging is correlated with specific nerve/muscle lesions and can guide the choice of nerves and muscles to evaluate in the ensuing EMG examination.

  • Serratus anterior (ie, long thoracic nerve) winging - The medial border of the scapula protrudes posteriorly and medially, with the inferior angle of the scapula rotating medially as well. Resisted protraction or forward flexion accentuates the winging. Abduction decreases the winging in this case.

  • Rhomboid (ie, dorsal scapular nerve, C5 root) winging - The scapula displaces laterally, with the inferior angle of the scapula rotating laterally, particularly with arm elevation over the head.

  • Trapezius (ie, spinal accessory nerve, C3-C4 roots) winging - The scapula translocates laterally, but the inferior angle rotates medially. Abduction accentuates this winging, and forward flexion decreases it. The shoulder also drops on the involved side, compared with the contralateral side.

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