[Proof of botulinum toxin antibodies with the Extensor Digitorum Brevis Test]

Abstract

Introduction: Some patients treated with botulinum toxin (btx) develop neutralizing btx antibodies (btx-ab). The expensive Mouse Diaphragm Bioassay (MDB) is considered as the gold standard by many authors. We wanted to examine whether the Extensor Digitorum Brevis Test (EDB test) is a reliable method to test for btx-ab.

Method: We performed an electroneurography of the m. extensor digitorum brevis on both feet of 23 patients with known MDB. Afterwards the right feet were injected with 25 U of btx, and 21-28 days later the electroneurography was performed on both sides again. Finally we correlated the measured values (muscular wave latency, amplitude, area, and duration) intraindividually and with the MDB results.

Results: The parameters area and amplitude correlated highly significantly with the MDB (P<0.001 for both tests). Decreasing the amplitude to at least 65% of its initial value indicated the presence of btx-ab. In that way 22 of 23 EDB classifications were identical to those of the MDB, yielding a sensitivity of 92.86% and a specificity of 100%.

Conclusion: The EDB test is a reliable technique for detecting btx-ab with high sensitivity and specificity. The EDB test can replace the MDB.