Nerve conduction study plays a key role in the correct diagnosis of HNPP

Abstract

Objective: As nerve conduction study (NCS) is a commonly employed tool in the diagnosis of hereditary neuropathy with liability to pressure palsies (HNPP), we describe the electrophysiological features of our patients, comparing the findings with those of healthy subjects. Methods: The charts of 19 HNPP patients were reviewed and NCS including residual latency (RL) and terminal latency index (TLI) were compared with the findings of 32 control subjects. Results: Motor NCS revealed significant differences (p<0.05) in all variables except for the tibial distal latency, median compound muscle action potential amplitude, ulnar and peroneal TLI, and tibial RL in the patient cohort compared with healthy controls. Tibial TLI was bigger in the patient cohort (p<0.05). Nerve conduction velocity (NCV) slowing of the knee-ankle segments were more marked compared with the elbow-wrist segments (p<0.05). NCV of the ulnar nerve was significantly slower in the elbow segment, compared with the below elbow-wrist and axilla-above elbow segments (p=0.000). F-responses were prolonged in the lower extremities and RL prolongations were especially prominent in the median nerve (p<0.05). TLI values were smaller in the median nerve, compared with all other nerves (p<0.05). Sensory NCS were notably abnormal in the patient cohort compared with the healthy controls (p<0.001). However, the sural compound nerve action potential amplitude was markedly enlarged compared with the upper extremity nerves (p<0.01). Conclusion: Correct interpretation of the NCS findings plays an essential role in the diagnosis and rational use of mutation analysis in suspected cases.