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

Conventionally, the standard test for detection of antibodies against botul inum toxin (BT-A) has been the mouse lethality assay (MLA). Because this te st 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 parti al subjective BT-A therapy failure underwent simultaneous MPA and MLA testi ng. 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 te st, p < 0.01). Sixteen samples showed discordant results. All of those were MPA-positive and MLA-negative. This excess of MPA-positive results was als o 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 pa rtial therapy failure. MPA and MLA results show significant association. St atistical analysis and predominance of partial therapy failure in MPA-posit ive patients demonstrate higher sensitivity of MPA. With its methodologic a dvantages, its test parameter being more relevant to BT-A therapy, and its higher sensitivity, the MPA appears to be superior to the MLA.