Comparison of mouse bioassay and immunoprecipitation assay for botulinum toxin antibodies

Abstract

Objective-To compare a recently developed immunoprecipitation assay (IPA) to the mouse protection bioassay (MPB), currently considered the "gold standard", for detecting antibodies against botulinum toxin A (BTX-A) and to correlate these assay results with clinical responses to BTX-A injections. Methods-MPB and IPA assays were performed on serum samples from 83 patients (38 non-responders, 45 responders) who received BTX-A injections. Six nonresponders had serum tested on two separate occasions. Some patients also received a "test" injection into either the right eyebrow (n=29) or right frontalis (n=19). Results-All patients antibody positive (Ab+) by MPB were also Ab+ by IPA, whereas an additional 19 patients (17 with reduced or no clinical response) who were MPB Ab− were Ab+, with low titres, by IPA. Two of these 19 patients (nonresponders) were initially MPB Ab− but later became MPB Ab+. Similar to previous studies, the sensitivity for the MPB was low; 50% for clinical, 38% for eyebrow, and 30% for frontalis responses whereas the IPA sensitivity was much higher at 84% for clinical (p<0.001), 77% for eyebrow (p=0.111, NS) and 90% for frontalis responses (p<0.02). The IPA specificity was 89% for clinical, 81% for eyebrow, and 89% for frontalis responses, whereas the MPB specificity was 100% for all three response types, which were all nonsignificant diVerences. Conclusions-Both assays had high specificity although the sensitivity of the IPA was higher than the MPB. In addition, the IPA seems to display positivity earlier than the MPB, and as such, it may prognosticate future non-responsiveness. Eyebrow and frontalis "test" injections correlated well with clinical and immunological results and are useful in the assessment of BTX non-responders. (J Neurol Neurosurg Psychiatry 1999;66:612-616)

Sudomotor testing predicts the presence of neutralizing botulinum A toxin antibodies

“…23 One exception probably is a recently developed radioimmunoprecipitation assay, 24 which has been demonstrated to correspond well to the results of different bioassays. 9,25 However, this test is expensive and not commonly available. The second possibility is to detect neutralizing ABAs with a bioassay.…”

“…The latter are the extensor digitorum brevis test 8 and the visual control of muscle function after injections into frontalis or eyebrow muscles in ABA-suspected patients. 9 These tests are useful; however, each of them has specific drawbacks: many in vitro tests are not specific enough to detect neutralizing ABA, and the mouse protection assay, for instance, results in the unavailing deaths of many animals.…”

Toxina botunílica tipo B no manejo de distonia não-responsiva a toxina botunílica tipo A

“…Ou seja, há quantidade apreciável de pacientes sem resposta clínica mas os testes são negativos e, pelo contrário, muitos têm teste positivo apesar de responderem normalmente a BTX-A. Por este motivo, alguns autores preferem usar testes clínicos para definir quem perdeu a resposta por motivos imunológicos: injeta-se um mús-culo bastante visível (frontal ou extensor dos dedos, por exemplo) e observa-se,em 30 dias, se sua ação foi bloqueada ou não 6 . Perda de resposta a BTX-A ocorre em 10-14% dos pacientes com distonia cervical tratados com injeções repetidas deste sorotipo.…”

“…On 8 sessions of BTX-A injections he received a cumulative dosage of 550U with a mean interval between sessions of 8.8 weeks (range [6][7][8][9][10][11][12]. Decline of response was noticed after the fifth session.…”

Therapeutic Application of Botulinum Toxin in Clinical Practice

“…Patients will experience relief of symptoms after each injection, followed by gradual resistance to further injection due to the development of neutralizing or blocking antibodies [10]. The mechanism of this resistance is unknown.…”