Topical photodynamic therapy (PDT) causes localized phototoxicity and has been shown both in vitro and in humans to have immunomodulatory and immunosuppressive effects. We report a case of localized bullous pemphigoid (BP) developing after PDT. Although BP has been reported to develop following cutaneous insults such as surgery, radiotherapy, psoralen ultraviolet A (PUVA) and ultraviolet B phototherapy, PDT has not previously been reported as a trigger. Possible mechanisms include direct mechanical injury to the basement membrane and subsequent autoantibody formation, an indirect immunomodulatory effect of PDT, or most likely, precipitation of BP in individuals with pre-existing low titres of epidermal autoantibodies (so-called subclinical BP). PDT should be added to the list of possible exogenous triggers for BP and this condition should be considered if blistering develops following PDT.
© 2011 John Wiley & Sons A/S.