Long-term changes in duration of relief with botulinum toxin treatment: Of essential blepharospasm and hemifacial spasm

Purpose: To determine long-term changes in duration of relief with serial treatments of botulinum A toxin (BAT) used to treat benign essential blepharospasm and hemifacial spasm, in view of conflicting reports as to whether BAT has an increasing, decreasing, or an unchanging duration of effect over a long period of treatment. Methods: Thirty-two patients with facial dyskinesia (20 with essential blepharospasm, 12 with hemifacial spasm) were followed between 5 and 9 years through a mean of 18 (range, 12-32) BAT treatments with prospective documentation of intervals of relief from symptoms. Repeated measures and linear regression analyses were used to determine trends in each group. Results: Marked inter- and intrapatient variability was found in the length of effect of BAT. Statistical analysis showed no significant changes in mean duration of relief within each group (P = 0.65 for essential blepharospasm, 0.36 for hemifacial spasm), There was a trend to slow decline in the interval of relief, especially in patients with an initial duration of effect greater than 150 days, No relation was found between duration of relief and age or sex of patient or grade and duration of disease before initial treatment. Conclusion: In the long term, the mean duration of relief from symptoms with BAT changes little over a period of serial treatments. Short-term fluctuations in the length of therapeutic effect did not indicate the development of a resistance to treatment.