Abstract

A 34-year-old otherwise healthy man presented with a 1-year history of extensive mildly itchy rash refractory to oral corticosteroids. Physical exam revealed pink plaques with silvery scale and follicular prominence overlying areas of patchy hypopigmentation, with focal areas of hyperpigmentation on the scalp, trunk, extremities, groin and gluteal cleft covering ~70% BSA. While a primary papulosquamous process like psoriasis was favored clinically, the morphology was unusual given the distinct hyperpigmented and hypopigmented areas. Laboratory workup (CBC, CMP, HIV, ANA, RPR, hepatitis serologies and tuberculosis testing) was unremarkable. Punch biopsy of a plaque on the upper back revealed hyperkeratosis with epidermal and adnexal hyperplasia and a dense band-like infiltrate of lymphocytes, histiocytes and many eosinophils that obscured the dermo-epidermal junction, where there were many necrotic keratinocytes. The histopathologic differential diagnosis included hypertrophic lichen planus and a lichenoid drug eruption. Given the clinical impression of hypopigmentation, a Mart-1 immunohistochemical stain was performed and revealed an absence of intraepidermal melanocytes, raising the possibility of vitiligo with a superimposed lichenoid dermatitis. Immunohistochemical staining for Treponemes was negative. In the absence of an inciting culprit medication, the patient was started on methotrexate and topical steroids, showing improvement within 1-month. Still, the clinicopathologic question remains whether this patient’s hypertrophic lichen planus represents a novel Wolf's isotopic response on sites of prior primary vitiligo, or a rare case of these two entities colocalizing with koebnerization due to scratching-induced trauma. This case highlights the rare colocalization of two inflammatory autoimmune conditions, suggesting the possibility of shared etiologic pathomechanisms.