To the Editor:
Erythema multiforme (EM) is an acute immune-mediated condition characterized by target-like lesions on the skin. Many factors have been implicated in the pathogenesis of EM, and infections and drugs being the most commonly identified triggers.1 EM following the lines of Blaschko (BL) is an extremely unusual pattern, and to the best of our knowledge, only 2 patients have been reported previously.2,3
An 18-year-old man presented with a 1-week history of a linear eruption on his right arm. The lesions consisted of target papules arranged in narrow bands that first appeared on his hand and spread to arm and trunk. He was taking no medication. There was no active or recurrent labial herpes. He had a history of atopic dermatitis. The family history was unremarkable.
Physical examination revealed a linear, erythematous, edematous, papular eruption extending from the first finger of his right hand to the ipsilateral trunk, involving the arm and shoulder in a multiple band-like pattern following BL (Fig. 1).
Laboratory examination revealed mild leukocytosis and positive antinuclear antibodies with a homogenous pattern (1:80). No other hematological, biochemical, or immunological abnormalities were demonstrated.
A punch biopsy taken from his arm showed interface dermatitis with a moderate infiltrate of lymphocytes that tended to obscure the dermoepidermal junction. Many apoptotic keratinocytes were present within and above the basal layer (Fig. 2).
Taking into account the clinical and histopathologic findings, the lesions were interpreted as EM along BL. The cutaneous lesions improved spontaneously in 4 weeks.
Distribution along BL is a pattern assumed by many different congenital and acquired dermatoses.4 It reflects possibly a form of “mosaicism” where certain specific cells or groups of cells react differently from other cells due to chromosomal abnormalities.4,5 In our patient, this could be the only explanation for the linear distribution of EM, whose trigger could not be established.
Most of the acquired dermatoses that present in a blaschkolinear pattern are common dermatoses that are usually distributed in a random fashion,6 such as lichen planus, lupus erythematosus, linear fixed drugs eruptions, and psoriasis. EM would be another example of a common dermatosis showing this unusual pattern.
Contrariwise, lichen striatus and adult blaschkitis (AB) always follow BL. In our patient, AB, an acquired relapsing eruption characterized by a papulovesicular dermatitis along BL,7,8 would be the main differential diagnosis. Nevertheless, histopathologically, AB shows spongiotic dermatitis, and only 2 patients exhibiting interface dermatitis have been reported previously.9,10 In both reports, EM was excluded based on clinical findings.
There are only 2 patients in the literature with EM along BL.2,3 Both cases affected young patients (20 and 28 years old) with no history of skin diseases, and both histopathologic studies showed an interface dermatitis. Regarding possible triggers, a history of recurrent labial herpes was reported in the first patient,2 and an active herpes labialis at the time of cutaneous lesions in the second patient.3
In summary, we report a patient with linear EM following BL without an identified trigger. The diagnosis is based on the distinct, targetoid-like, cutaneous lesions, histopathologic features, and the absence of relapses that characterizes AB.6,8
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