P072 : An atypical case of lichen striatus showing clinical features of lichen planus pigmentosus

Lichen striatus is a rare, self-limited dermatosis prevalent in children. Blaschkoid linear distribution of flat-topped papules is a well-known feature of the disorder. Lichenoid reaction with perivascular and appendageal lymphocytic infiltrate is a classic pathologic finding of the disease. On the other hand, lichen planus pigmentosus is a variant of lichen planus with characteristic hyperpigmented dark-brown macules. A 31-month-old girl visited our clinic with flat-topped pink-to-brown papules on left thigh and knee lasting more than 3 months despite application of topical steroids. Punch biopsy was executed at the most severe site of the lesion. The pathologic specimen showed lichenoid dermatitis pattern with perivascular and periadnexal lymphocytic infiltration. The biopsy was best matched with the diagnosis of lichen striatus. The patient started treatment with prednicarbate lotion and tacrolimus ointment. However, during the treatment, the lesion exacerbated into confluent purple to dark-brown colored patches. The developed lesion was clinically suspicious for lichen planus pigmentosus. The lesion gradually faded over more than three months with use of tretinoin cream. Herein, we present a case of lichen striatus with atypical features resembling lichen planus pigmentosus.