Positive controls, neutralizing antibody

A multicenter, double-blind, randomized, placebo-controlled study in 320 patients with untreated hyperhidrosis showed a more than 50% reduction in sweat production at 4 and 16 weeks after treatment respectively in 94 and 82% of patients treated with botulinum toxin (50 MU per axilla) and in 36 and 21% of placebo-treated patients (7). The major treatment-related adverse effect was an increase in sweating in non-axillary sites after treatment. Open treatment with botulinum toxin A was offered to patients in whom sweat production was at least 50% of baseline values (8). Of 207 study subjects, 39% had one treatment, 45% had two treatments and 15% had three treatments. Response rates 4 weeks after treatment were 96, 91, and 83% after the first, second, and third treatments respectively. In one of 207 patients there was possible transient seroconversion from negative to positive for neutralizing antibodies to botulinum toxin, and subsequent treatment with botulinum toxin resulted in complete disappearance of axillary sweating 7 days after injection. 

It is a good practice, although time-consuming and costly, to confirm positive reactions with blocking tests (reaction of the antigen with antibodies from an independent source, prior to the addition of the test serum) or neutralization tests (treatment of the test serum with antigen, prior to the addition to the antigen-coated solid phase). If available, pre-infection sera should also be tested, as well as non-immune sera, as controls. 

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