Purpose: Conflicting data have been reported regarding development of serum antibodies to botulinum A toxin. The purpose of this study is to determine conclusively whether antibody production to this toxin occurs in humans, and, if so, to determine its relationship, if any, to length of treatment, total cumulative dose, and clinical response to treatment. Methods: Sixty-five sera samples from 42 adults treated with botulinum A toxin for essential blepharospasm, hemifacial spasm, or spasmodic torticollis were analyzed via a sphere-linked immunodiagnostic assay for antibody production. Results were plotted against length of treatment, number of injections, cumulative dose, and treatment effect produced. Results: Twenty-four (57%) of the 42 patients produced antibodies in all three diagnostic groups. No significant differences were found between antibody producers and nonproducers with respect to age (P = 0.216), length of treatment (P = 0.586), number of injections (P = 0.619), or total cumulative dose (P = 0.286). Within the antibody-producing group, there was no significant correlation between amount of antibody and length of treatment (P = 0.081), number of injections (P = 0.134), or cumulative dose (P = 0.250). The presence of demonstrable antibodies in serum did not affect the clinical responsiveness to injection. Conclusion: Antibody production is present in a majority of patients treated with botulinum A toxin. The sphere-linked immunodiagnostic assay is a reliable and reproducible method for detecting and quantifying these antibodies. When antibody production occurs, it is likely due to variations in individual immune responsiveness and appears to have no direct effect on the patient's clinical response to treatment.
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