Botulinum toxin: evidence-based medicine criteria in rare indications.

Presently, there are more than 50 possible indications for the application of botulinum toxin. In some indications the use of botulinum toxin has already been approved; others are about to be approved. For most of these indications a sufficient number of studies have been published. For rare indications, an insufficient number of studies are available. In part there are only published case reports. Classification according to the criteria of evidence-based medicine is thus difficult. Here we try to describe the range of possible indications for botulinum toxin A and assess its therapeutic value for rare indications. The number of studies available on botulinum toxin B is still limited.