BLASCHKOID LICHEN PLANUS IS A RARE AND PROBABLY UNDER-RECOGNIZED VARIANT OF LICHEN PLANUS

Abstract

Introduction: Lichen planus (LP) is a chronic inflammatory dermatosis characterized by violaceous, flat-topped papules and plaques. It has several clinical variants, of which Blaschkoid lichen planus (BLP) is an uncommon presentation. BLP is characterized by lesions following the embryonic lines of Blaschko, often producing linear, curvilinear, whorled, or S-shaped patterns. Differentiation from linear LP is important, as the latter may result from Koebnerization or other mechanisms and does not necessarily follow Blaschko lines. BLP may also clinically resemble other Blaschkoid dermatoses, particularly lichen striatus, making clinicopathological correlation essential. Most reported cases demonstrate unilateral involvement, while bilateral or extensive Blaschkoid distribution is less frequently described.

Case report: 12 yr old female presented with mildly pruritic lesion over chest, left arm and left forearm for 3-4 months. The eruption initially appeared over left side of chest then gradually spreading to involve left arm and left forearm. There was no history of preceding trauma or other dermatological condition. No history of varicella either and patient was not on any medication. Upon closer inspection, several violaceous papules and plaques with a clear hyperkeratotic edge were found closely arranged in a linear pattern along the lines of Blaschko (LB) on the chest and left side upper limb. The child’s developmental milestones were normal, and a thorough systemic examination was also normal. Differential diagnoses considered were porokeratosis and LP. Skin biopsy from the right forearm showed a epidermis with hyperkeratosis and orthokeratosis showing basal cell vacuolation. Superficial dermis reveals melanophages and lympho-histiocytic infiltrate. In view of the characteristic Blaschkoid distribution, violaceous lichenoid morphology and supportive histopathological findings, a diagnosis of Blaschkoid lichen planus was made, and the patient was treated with topical steroids.

Conclusion: Blaschkoid lichen planus is a rare and probably under-recognized variant of LP, particularly in children. Recognition of the characteristic Blaschkoid distribution, together with the typical lichenoid morphology and supportive histopathological findings, is essential for diagnosis. Careful differentiation from lichen striatus and other linear dermatoses is important, particularly in the pediatric population. The present case is noteworthy because of its occurrence in a 12-year-old child and the characteristic unilateral Blaschkoid distribution, highlighting the variable clinical presentation of this uncommon variant.