What is the role of sensory assessment in electrodiagnostic medicine?

Updated: Aug 06, 2019
  • Author: Brian M Kelly, DO; Chief Editor: Stephen Kishner, MD, MHA  more...
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Answer

Answer

Assess pain or temperature, light touch, vibration, and position sense, as well as, if necessary, discriminative sensations (such as 2-point discrimination and stereognosis, if cortical lesions are suggested).

Because all sensory lesions above the dorsal root ganglion do not cause standard sensory NCS abnormalities, the first aspect of the sensory examination is to attempt to differentiate cortical, central or lateral cord, or posterior column abnormalities. Differentiating pain and temperature (central cord or lateral spinothalamic tract) from vibration, as well as position sense (posterior columns) versus light touch (anterior spinothalamic and posterior column), sometimes can help in this effort.

The second step in the sensory examination is to define a pattern where possible. Understanding typical peripheral nerve distributions and dermatomal (ie, radicular) distributions clearly is very useful. For example, the patient with complaints of a numb thumb may have any of multiple possible etiologies, from digital nerves to the brain. The examination finding of sensory abnormality may well be different than the complaint.

If sensory examination results show abnormalities along the volar thumb, index finger, middle finger, and half of the ring finger, median nerve dysfunction may be suggested, as opposed to abnormality of the volar and dorsum of the thumb and index finger with additional findings along the distal forearm suggesting C6 root abnormality instead. Nondermatomal and nonperipheral nerve distribution abnormalities may indicate polyneuropathic problems for which distal versus proximal patterns need to be assessed. Finally, an attempt to clarify the type of sensory abnormality is important. For example, hyperalgesia, and allodynia may imply small, unmyelinated C-fiber or autonomic nerve dysfunction not seen on standard sensory NCS.


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