[Electrophysiological study on pathophysiology of Bell's palsy--distribution of nerve conduction velocities (DNCV) in facial nerve with collision method].

The etiology of Bell's palsy is still obscure, but the hypothesis that hypoxia and compression of the nerve induced by edema in the Fallopian canal are the main causes of Bell's palsy is widely accepted. Tojima (1988) reported that the motor nerve conduction velocity (MCV) gradually decreased as degeneration of the nerve fibers progressed in Bell's palsy. The majority of facial nerve fibers are myelinated, and the greater the fiber diameter, the faster the conduction velocity. For this reason, Tojima suggested that Wallerian degeneration in Bell's palsy would begin from the thicker myelinated fibers. The measurement of MCV, however, reveals only the activities of the fastest velocity motor nerve fiber in the nerve trunk. This weak point can be resolved by measurement of the distribution of nerve conduction velocities (DNCV), which was introduced by Hopf in 1962 as the collision method. In the present report, the DNCV of facial nerve was measured using the collision method to estimate the distribution of the diameter of nerve fibers in normal subjects and patients with Bell's palsy and to elucidate the pathophysiology of Bell's palsy. The subjects were 14 normal adults (19 measurements) and 14 patients with Bell's palsy who visited our university clinic within 7 days to 18 days after onset, with no other complications such as diabetes. Results obtained are as follows. 1) The mean DNCV in 14 normal subjects (19 measurements) was unimodal, showing a peak at 20 to 22 m/s. 2) In DNCVs of patients with Bell's palsy, loss of thicker fibers with faster conduction velocity was recognized (11/14, 79%).(ABSTRACT TRUNCATED AT 250 WORDS)