DP29 Tumour mimic in dermatopathology: a rare case of granulomatous pigmented purpuric dermatosis

Abstract

A 72-year-old White woman, with a background of chronic inflammatory demyelinating polyradiculoneuropathy, presented with a large violaceous patch on the left upper inner thigh, surrounded by multiple satellite brown macules and petechial lesions. The patient described a long-standing ‘birthmark’ at the site since childhood, with gradual development of pinpoint satellite lesions over 18 months and a newer painful boggy swelling involving the left buttock evolving over 6 months. This clinically raised concern for angiosarcoma, haematoma or another vascular neoplasm. Examination demonstrated a vascular-appearing erythematous lesion on the medial thigh with prominent violaceous discoloration, petechiae extending down the thigh, and a soft boggy buttock swelling with overlying blue-purple hue. There was no lymphadenopathy present. Three punch biopsies from the left medial thigh (upper and lower) and left buttock showed similar histological features: normal epidermis with a dense lymphohistiocytic infiltrate in a lichenoid, perivascular and periadnexal distribution, with a prominent granulomatous component and conspicuous haemosiderin-laden macrophages. Interface vacuolar change and keratinocyte apoptosis were absent, and eosinophils were rare. No evidence of vasoformative malignancy or atypical endothelial proliferation was identified. The overall features supported a diagnosis of granulomatous pigmented purpuric dermatosis (GPPD), a rare variant of pigmented purpuric dermatosis. In this case it presented with striking tumour-mimicking clinical morphology in the context of a presumed congenital vascular patch. This case is significant as pain and tumour-mimicking vascular clinical appearances are distinctly uncommon in GPPD, broadening the recognized clinicopathological spectrum and highlighting the importance of biopsy in excluding malignancy and preventing unnecessary aggressive management.