Botulinum toxin antibody testing: comparison between the immunoprecipitation assay and the mouse diaphragm assay

Antibodies against botulinum toxin (BT) are currently best detected by the mouse diaphragm assay (MDA). Nevertheless, the MDA still has disadvantages, so that an immunoprecipitation assay (IPA) was introduced recently. We sought to compare the results of both tests. 33 samples from patients with cervical dystonia and complete or partial BT therapy failure underwent blinded simultaneous IPA and MDA testing. 27 (82%) samples showed concordant results, 17 (52%) being positive and 10 (30%) negative for both IPA and MDA resulting in a significant association of the dichotomous test results (Fisher's exact test, p < 0.01). The other six samples (18%) showed discordant results, all being IPA-negative and MDA-positive. This excess of MDA-positive results was also significant (Sign rank test, p = 0.03). IPA and MDA results showed a very strong and significant qualitative and quantitative association. The IPA seems to be less sensitive than the MDA for detection of low BT-AB titres, but the clinical relevance of this still needs to be established. Since the IPA is simpler, faster and cheaper than the MDA and avoids sacrifice of animals, it could become the preferred BT-AB test.