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

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.

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.

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%.

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