Response and immunoresistance to botulinum toxin injections.

Botulinum toxin antibodies (ABS) may be a reason why occasionally patients do not have a response to injections with botulinum toxin type A (BTX). We tested 86 patients with cervical or oromandibular dystonia for the presence of BTX ABS; 20 were positive and 66 were negative. All patients who tested positive had no response to BTX injections on at least two consecutive treatment sessions. When compared with 22 randomly selected patients with negative BTX ABS results, the patients with positive BTX ABS tests had an earlier age at onset (mean age: 31.8 +/- 16.7 years versus 43.4 +/- 10.5; p < 0.05), higher mean dose per visit (249.2 +/- 32.5 U versus 180.8 +/- 68.7, p < 0.0005), and higher total cumulative dose (mean dose: 1,709 +/- 638 U versus 1,066 +/- 938; p < 0.01). Four out of five patients with positive ABS tests later had a response to botulinum toxin type F injections. Of 26 patients with negative BTX ABS results who were tested because of poor response on at least one visit, 21 had good response after subsequent injection and five had no effect. Except for young age at onset and higher dosages, there were no other factors that could reliably predict which patients would become immunoresistant to BTX type A injections. Treatment with alternate serotypes may offer clinical benefit to this group of patients. Absence of detectable BTX ABS may occur in patients with poor response to BTX injections because of inadequate dosage, injections of inappropriate muscles, or poor sensitivity of the BTX ABS bioassay.