Clinical and electrophysiologic evaluation of peripheral nerve function in chronic phenytoin therapy

Analysis of covariance was employed to explore possible correlations among duration of phenytoin therapy, phenytoin and folate serum concentrations, and clinical and electrophysiologic findings in 32 patients receiving single phenytoin therapy. None of our patients volunteered peripheral nervous system complaints. On examination, 9 of 32 (28%) were found to have signs suggestive of neuropathy (absent knee and/or ankle jerks). Neither phenytoin serum concentration nor duration of phenytoin therapy was found to significantly (p greater than 0.05) affect nerve function after an adjustment for age differences. A test for overall effect of folate serum concentration (grouped greater than or equal to 5 or less than 5 ng/ml) also failed to reach statistical significance (p greater than 0.05). Our findings suggest that phenytoin and folate serum concentrations and duration of phenytoin therapy do not have an important role in the development of clinical neuropathy and electrophysiologic abnormalities.