Mouse bioassay versus Western blot assay for botulinurn toxin antibodies Correlation with clinical response

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Abstract
Objective To compare the mouse protection bioassay (MPB) to the Western blot assay (WBA) in detecting antibodies against botulinum toxin A (BTX-A) and to correlate the assay results with clinical responses to BTX-A injections. Methods MPB and WBA assay results were compared in 51 patients (34 nonresponders and 17 responders) who received BTX-A injections, most commonly for cervical dystonia. A subset of patients received a “test” injection into either the right eyebrow (14) or right frontalis (12). Results Twelve patients with antibodies against BTX-A (Ab+) detected by WBA did not demonstrate antibodies (Ab-) by MPB. Conversely, five patients were Ab+ by MPB but Ab— by WBA. Specificity of the MPB was 100% on all three parameters (clinical, eyebrow, and frontalis injections), whereas WBA specificity was only 71% for clinical response but 100% for both eyebrow and frontalis responses. Sensitivities for both assays were low (33 to 53%). Of the 16 patients previously Ab+ by MPB, seven became negative on retesting after a mean interval of 33 months (range, 6 to 93 months). Conclusions The lower specificity of the WBA compared to the MPB suggests that the WBA detects nonblocking antibodies. Eyebrow and frontalis “test” injections correlated well with MPB and WBA results and with clinical responses and may be useful in the evaluation of BTX nonresponders.

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