A controlled trial of isoniazid therapy for action tremor in multiple sclerosis

Ten patients with clinically definite multiple sclerosis (MS) and action tremor were treated with isoniazid (INH) in a double-blind single crossover trial. The daily dose of INH administered during the 4-week treatment phase of the trial was determined by acetylator phenotype with slow acetylators receiving 12 mg/kg per day and rapid acetylators 20 mg/kg per day. Six of eight patients who completed the trial showed clinical improvement in the postural (alternating) tremor while on INH but the degree was minimal in all cases. Results of tremograms indicated that improvement also occurred in the intentional (synchronous) component of three patients while on INH, but this did not achieve statistical significance. Cerebrospinal fluid (CSF) levels of gamma-aminobutyric acid (GABA) homocarnosine and ornithine were markedly elevated with INH therapy (providing evidence for substantial inhibition of GABA aminotransferase activity and increase in GABA in the CNS), but no correlation was found between the degree of GABA elevation in the CSF and the clinical response. Side effects were minimal and well tolerated. Although INH appears to have a limited therapeutic role, a trial is warranted in MS patients with postural tremor.