[Adult blaschkitis (lichen striatus) in a patient treated with adalimumab].

Lichen striatus is an acquired inflammatory dermatosis that usually presents in children as papules arranged in a single band following the Baschko lines on an extremity. The disorder resolves slowly, leaving transient hypopigmentation, and rarely recurs. Histopathology findings indicate both lichenoid and spongiotic dermatitis. A variant of blaschkitis that occurs in adults is referred to as adult blaschkitis, acquired relapsing self-healing Blaschko dermatitis, or acquired Blaschko dermatitis. Characterized by papulovesicles grouped in multiple ipsilateral blaschkoid bands, adult blaschkitis typically affects the trunk. It resolves rapidly without sequelae, but relapses are frequent. Histopathology reveals a predominance of spongiotic dermatitis (Table 1).1-3 Disagreement has arisen in recent years, given that cases have been reported in which there have been marked clinical and histopathological similarities between blaschkitis and lichen striatus.3 This has led to the disorders being classified under the term Blaschko l inear acquired inf lammat ory skin erupt ion, with adult blaschkitis included under lichen striatus, or with both these considered as opposite poles of the same disease.2,4 The etiology of these dermatoses is unknown, although they have been associated with a personal or family history of atopy. Triggering factors have occasionally been identified, such as infections (eg, varicella), vaccines, pregnancy, stress, drugs (eg, metronidazole), skin trauma, and contact dermatitis.3,5 We describe the case of a 44-year old man with plaque psoriasis, who developed adult blaschkitis 2 months after commencing treatment with adalimumab. The patient, with a past history of gonarthrosis and tonsillectomy, had been diagnosed with plaque psoriasis 13 years earlier. The psoriasis had been treated with methotrexate and phototherapy (psoralen plus UV-A radiation and narrowband UV-B radiation). After an exacerbation of the psoriasis (a psoriasis area and severity index (PASI) score of 11.60), subcutaneous treatment was commenced with adalimumab in accordance with the standard protocol. Follow-up at 3 months showed an improvement in the psoriasis lesions (PASI score, 6.40). Several bands of slanted S-shaped erythematous papules were also observed in the right abdominal region, on the right flank and right buttock, and in the proximal area of the right thigh, following the Blaschko lines and sharply interrupted midline (Figure 1). The patient reported that the skin rash had appeared gradually over the previous 3 weeks and was pruritic. He had no personal or family history of atopic dermatitis. Biopsy revealed a predominantly lymphocytic inflammatory infiltrate in the dermis, affecting small patches in the papillary dermis and upper part of the mid dermis, and most concentrated around the follicles. The epidermis was normal except for discrete spongiosis (Figure 2). Adalimumab is a recombinant human monoclonal antibody for immunoglobulin G1 isotype which inhibits tumor necrosis factor (TNF) a. It is effective in the treatment of moderate to severe plaque psoriasis. Like other TNF-a inhibitors, it can, paradoxically, cause inflammatory skin disorders, particularly psoriasis or psoriasiform rash.6 Eruptions with lichenoid histopathology have also been described, but