How is the sensory portion of the peripheral nervous system tested?
Sensory NCS are the primary means to test the integrity of the sensory nerves. The amplitude of SNAP, its point of onset, and its peak can be compared with standardized normal values and with those from the opposite extremity. Sensory NCS are only abnormal in lesions distal to the dorsal root ganglia where sensory neurons reside. Abnormal SNAPs can be an important way of distinguishing between peripheral neuropathies or plexopathies and radiculopathies. In the latter, SNAPs are usually normal even when a patient complains of numbness. Using the complementary information obtained from needle EMG examination, an electromyographer can further localize the lesion to a particular spinal nerve root, portion of the plexus, or a particular peripheral nerve.