Skin reactions after intramuscular injection of Botulinum toxin A: a rare side effect.

The use of Botulinum toxin as a treatment for dystonia and other neurological conditions has been rapidly increasing over the past decade. In general, idiosyncratic adverse reactions to repeated injections of Botulinum toxin seem to be rare and were described in only a few recent reports. We present two cases of substantial skin reactions, one with systemic involvement, after intramuscular application of Botulinum toxin A. The possible role of immunologic factors and other mechanisms such as intolerance and pseudoallergic reaction are discussed. We would like to alert the clinician to this rare, but occasionally serious side effect that may be underestimated.