Botulinum toxin antibody titres: measurement, interpretation, and practical recommendations

Area of Science:

• Neurology
• Immunology
• Pharmacology

Background:

• Botulinum toxin (BT) therapy can fail due to the development of antibodies (BT-AB).
• Existing methods for detecting BT-AB include the mouse lethality assay (MLA), mouse diaphragm assay (MDA), and sternocleidomastoid test (SCMT).
• The correlation between these tests and patient-reported therapy failure is not well-established.

Purpose of the Study:

• To compare the three main BT-AB detection methods (MLA, MDA, SCMT).
• To correlate BT-AB test results with subjective reports of secondary therapy failure in cervical dystonia patients.
• To establish reliable thresholds for BT-AB detection indicating therapy failure.

Main Methods:

• Comparison of MLA, MDA, and SCMT in 37 cervical dystonia patients experiencing therapy failure.
• Correlation analysis between BT-AB test results and patient complaints of complete or partial secondary therapy failure.
• Evaluation of BT-AB titres and their correlation with BT's paretic effect.

Main Results:

• Patient complaints of therapy failure did not correlate with any of the BT-AB tests.
• MDA and MLA showed strong correlation, suggesting MDA could replace MLA as the gold standard.
• SCMT results were also correlated with MDA and MLA, indicating a functional balance between BT-AB titres and BT's efficacy.

Conclusions:

• While patient-reported failure wasn't linked to BT-AB tests, the MDA and MLA are highly correlated, with MDA potentially replacing MLA.
• The SCMT also correlates, supporting the concept of a functional balance between BT-AB levels and treatment effectiveness.
• Specific thresholds for MDA (>10 mU/ml), MLA (>3), and SCMT (<25%) strongly suggest BT-AB induced therapy failure; lower MDA values (<0.6 mU/ml) are therapeutically irrelevant.