Prevalence of neutralising antibodies in patients treated with botulinum toxin type A for spasticity.

Botulinum toxin (BT) has been used with great success to treat various muscle hyperactivity disorders. Occasionally, antibodies against BT (BT-AB) can be formed. When they are directed against the neurotoxin component of the BT drug, they are called neutralising antibodies. They can reduce the therapeutic effect partially or completely. We have measured neutralising BT-AB by use of the mouse diaphragm assay (MDA) in 42 adult patients with spasticity in the order of their appearance in the clinic. The patients had been treated for at least 2 years with BT type A (BT-A) and received on an average 14.2 +/- 6.1 BT-A injection series. BT-A was applied as Botox only, Dysport only or by sequential application of both preparations. The mean cumulative doses were 4,610 +/- 1,936 units Botox and 14,033 +/- 7,566 units Dysport, respectively. The mean treatment time was 4.5 +/- 1.8 (2-8) years. All patients were initially responsive to BT-A therapy. MDA detected BT-AB in 12% (5/42) of patients. However, in three patients the BT-AB titre was very low (<0.3 mIU/ml), in one it was intermediate (0.6 mIU/ml) and in one patient it was high (>1.0 mIU/ml). All BT-AB negative patients and also two of the patients with low BT-AB titre remained clinically responsive to BT therapy throughout the study. In conclusion, prevalence of BT-AB formation with clinical relevance (6%, 3/42) in adult patients with spasticity is not higher than that of BT-treated patients with cervical dystonia and much lower than that of BT-treated patients with infantile cerebral palsy.