Prolonged dermatitis distant to the site of squaric acid dibutyl ester applications and recovery of alopecia areata

Squaric acid dibutyl ester (SADBE) is a potent contact sensitizer that has been widely used for treating recalcitrant alopecia areata.1 However, the underlying precise mechanism of the therapeutic effects of SADBE immunotherapy has not yet been fully elucidated. We report a case with diffuse alopecia areata treated with SADBE solution that resulted in a complete regrowth of hair, but also showed widespread eczematous dermatitis on the face, neck and chest. We think this case may provide more evidence about the mechanism of action of SADBE in the treatment of alopecia areata. It also warns clinicians of the associated risks. A 24‐year‐old Japanese woman presented with a 10‐month‐history of diffuse alopecia on the scalp and eyebrows, which was refractory to therapies including topical corticosteroids and cryotherapy (Fig. 1a). We sensitized her with 1% SADBE in acetone and, 2 weeks later, we started a weekly application of 0.0001% SADBE solution to the scalp. As she obtained an appropriate allergic response, the concentration of the applied solution was gradually increased to 1%. After 12 weeks of treatment, she had shown a considerable regrowth of hair on the scalp (Fig. 1b). We also found significant hair growth of the eyebrow hair, to which we had not applied the SADBE solution. In spite of the good efficacy of the SADBE treatment, she developed brown to erythematous patches on her periorbital and forehead skin with itching and discomfort (Fig. 1d). Patch tests performed with cleansing cream, shampoo, soap, and cosmetics, were all negative. Although treatments for her dermatitis with steroid ointment and oral antihistamines were initiated and the SADBE was discontinued, the dermatitis on the face spread to her neck, nape and chest. It resolved in 12 months. At 24 months, after the cessation of SADBE application, the alopecia had not recurred on the scalp or eyebrows (Fig. 1c).