Positive Antinuclear Antibody and Blaschkoid Lichen Planus Pigmentosus.

Lichen planus pigmentosus is a rare variant of lichen planus. It is an acquired pigmentary disorder of unknown etiology. It is characterized by dark brown and slate gray macules and patches. The nails, scalp, and oral mucosa are usually spared, unlike lichen planus. Lichen planus pigmentosus commonly involves the head and neck region as well as intertriginous areas such as the axillae, inframammary and inguinal regions. It can be associated with autoimmune diseases, endocrinopathies, and other variants of lichen planus such as fibrosing alopecia of the scalp. Variable clinical patterns of lichen planus pigmentosus including zosteriform, linear, and segmental had been published. Histopathologically, it is characterized by hyperkeratosis of the epidermis, hypergranulosis, variable degrees of lichenoid infiltration depending on the age of the lesion, and prominent melanin incontinence. Recent updates on erythema dyschromicum perstans that were considered similar to lichen planus pigmentosus, concluded that they could be differentiated on clinical bases as well as histopathology. Epidermal hyperkeratosis, hypergranulosis, apoptotic cells, lichenoid dermatitis, periappendageal infiltrate, and fibrosis with marked superficial dermal melanin incontinence aid to differentiate lichen planus pigmentosus from erythema dyschromicum perstans. During embryogenesis, cells migrate and follow developmental lines named after Blaschko, a German dermatologist, who first noted them. Blaschko's lines (BL), do not follow neural, vascular, or lymphatic pathways. They appear as V-shaped on the back, S-shaped on the abdomen, and linearly on limbs. We report a case of lichen planus pigmentosus over BL that is a rare presentation of the disease and associated positive antinuclear antibody (ANA) without overt manifestations of any connective tissue disease.