Unusual Co-Presentation of Two Skin Patterns in a Case of Granulomatosis with Polyangiitis: A Case Report and Literature Review.

Introduction: Granulomatosis with polyangiitis (GPA) is a rare necrotizing granulomatous vasculitis that affects small-to-medium-sized vessels. Cutaneous involvement is common, but highly variable in morphology, complicating diagnosis. Herein, we present a case of GPA co-presenting with two skin patterns. Case Presentation: A 61-year-old Thai woman presented with chronic cough, constitutional symptoms, and weight loss. Chest computed tomography revealed multiple pulmonary nodules, and lung biopsy showed chronic granulomatous inflammation. Subsequently, the patient developed rapidly progressive glomerulonephritis with crescent features. During hospitalization, she exhibited two distinct cutaneous morphologies: erythematous hyperkeratotic umbilicated papules with crusting on both elbows and erythematous-to-violaceous vesiculopapules on both auricles. Histopathological examination of the elbow lesions revealed features consistent with early palisaded neutrophilic granulomatous dermatitis (PNGD), whereas the auricular lesions demonstrated bullous vasculitis. Although the 2022 ACR/EULAR GPA classification score was below the diagnostic threshold, the multidisciplinary team concluded that clinical, histopathological, and radiological findings supported the diagnosis of GPA. The patient responded well to immunosuppressive therapy, including intravenous methylprednisolone, cyclophosphamide, and plasma exchange therapy. Conclusions: This case shows an unusual combination of bullous vasculitis and PNGD in a patient with GPA, highlighting the importance of recognizing uncommon skin lesions as possible clues to underlying systemic vasculitis.