Botulinum toxin antibody testing: Comparison between the mouse protection assay and the mouse lethality assay

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Abstract
Conventionally, the standard test for detection of antibodies against botulinum toxin (BT‐A) has been the mouse lethality assay (MLA). Because this test has a number of disadvantages, a novel mouse protection assay (MPA) was recently introduced. We sought to compare the results of both tests. Forty‐three samples from 38 patients with cervical dystonia and complete or partial subjective BT‐A therapy failure underwent simultaneous MPA and MLA testing. Twenty‐seven samples showed concordant results in both tests. Eleven of them were MPA‐ and MLA‐positive and 16 MPA‐ and MLA‐negative, resulting in a significant association of the dichotomous test results (Fisher exact test, p <0.01). Sixteen samples showed discordant results. All of those were MPA‐positive and MLA‐negative. This excess of MPA‐positive results was also significant (Wilcoxon signed‐rank test, p <0.001). Of the patients with MPA‐positive samples, 62% had complete and 38% had partial therapy failure. Of the patients with MLA‐positive samples, 90% had complete and 10% had partial therapy failure. MPA and MLA results show significant association. Statistical analysis and predominance of partial therapy failure in MPA‐positive patients demonstrate higher sensitivity of MPA. With its methodologic advantages, its test parameter being more relevant to BT‐A therapy, and its higher sensitivity, the MPA appears to be superior to the MLA.

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