Topical immunotherapy and its use in alopecia areata

Abstract

Topical immunotherapy is a well-documented option for treating alopecia areata, especially extensive and recalcitrant types. At present, squaric acid dibutyl esterase (SADBE) and diphenylcyclopropenone (DPCP) are currently in use, while dinitrochlorobenzene (DNCB) was discontinued due to having carcinogenic properties. The mechanism of topical immunotherapy is not well-established. The main hypothesis is antigenic competition shifting the target of abnormal immune cells from attack hair follicle to the applied site, thus producing delay-type hypersensitivity. In vivo studies have demonstrated an increase in cytokines that represent the activity of T-cells, NK cells. In terms of clinical efficacy in the treatment of AA, DPCP and SADBE have shown effective and satisfactory results. Although the results vary, it can be expected to see full regrowth in one-third of patients. Patients have to be sensitized with 2-3% DPCP or 2% SADBE at first, then continue to apply topical immunotherapy starting from the lowest concentration and titrated up in order to get the optimum concentration that causes mild dermatitis. Next, the optimum concentration is applied on the bald area weekly. The hair will start regrowth after 3 to 6 months. Patients who fail to respond after 6 months will be defined as non-responders. However, one study after follow up for 5 years showed that 30% of patients could have regrowth after 6 months. Even if patients have hair regrowth, the relapse rate is around 50%. Therefore, maintenance protocol might apply in this group of patients. DPCP and SADBE are generally well tolerated in alopecia areata patients. Regular adverse events are local or spreading dermatitis and local lymphadenopathy. Other essential but less common side effects are urticaria, angioedema, erythema-multiforme like reaction, and pigmentary change. The side effects are not only exhibited in treated-patients, but also in their spouses or close family members who have contact with them after residual topical immunotherapy. Thus, physicians should inform patients to strictly follow the advice after the application. Children with AA are not recommended to use topical immunotherapy due to the lack of long term toxicity data and the nature of the disease, which usually has poor prognosis compared to adults. Nevertheless, studies in children have found that topical immunotherapy is effective and satisfactory; Side-effects are also similar to adults