Topical immunotherapy is universally used for the treatment of alopecia areata. The purpose of the treatment is to induce a mild contact dermatitis that may induce hair regrowth by mechanisms still unknown. Suggested mechanisms include antigenic competition, nonspecific systemic suppression of delayed-type hypersensitivity reactions, and interference with proinflammatory cytokine activity.
Chemicals currently used for topical immunotherapy are squaric acid dibutylester and diphencyprone. Topical immunotherapy is usually well tolerated, and adverse effects, including eczematous reactions, facial and scalp edema, neck lymphadenopathy, contact urticaria, vitiligo, pompholyxlike eruption, erythema multiforme, and postinflammatory hyperpigmentation or hypopigmentation,1 are mild and reversible. Pigmentation of the treated area is commonly observed (up to 12.2% of cases),2 especially in patients with dark skin. We describe a previously unreported adverse effect of topical immunotherapy: the development of widespread lentigines.
Tosti A, Piraccini BM, Misciali C, Vincenzi C. Lentiginous Eruption Due to Topical Immunotherapy. Arch Dermatol. 2003;139(4):544-545. doi:10.1001/archderm.139.4.544