Botulinum toxin type B de novo therapy of cervical dystonia
Botulinum toxin induced therapy failure type B antibody (BT–B, BT–B–AB) has so far only been reported after previous formation of antibodies against botulinum toxin type A (BT–A, BTA– AB).We wanted to explore the risk of BT-B-AB-induced therapy failure in patients who were exposed to botulinum toxin for the first time.
For this purpose we followed nine patients with cervical dystonia receiving BT-B (NeuroBloc®/Myo- Bloc™, Elan Pharmaceuticals) in a dose of 11435 ± 2977MU during 4.9 ± 3.0 injection series. All patients showed a satisfactory initial therapeutic response as documented by a Toronto Western Spasmodic Torticollis Rating Scale score reduction from 17.7 ± 9.4 to 5.3 ± 4.8 and an overall subjective improvement of 56.1 ± 28.3%. Seven patients experienced systemic anticholinergic side effects. Five patients had stable therapeutic responses over subsequent injection series. Four patients experienced complete therapy failure with BT–B–AB titres in excess of 10mU/ml on the mouse diaphragm assay. Doubling the last effective BT–B dose produced neither therapeutic effects nor side effects. Subsequent applications of botulinum toxin type A produced a continued therapeutic response in one patient and complete therapy failure in the other.
Despite the small sample size a frequency of 44 % indicates a high risk for BT–B–AB-induced complete therapy failure. The high amount of neurotoxin administered when NeuroBloc®/MyoBloc™ is used might be a contributory factor. Further prospective comparative studies are necessary to monitor the frequency and time course of BT–B–AB formation.
Key wordsbotulinum toxin type B therapy failure de novo therapy botulinum toxin type A electromyography antibody formation
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