Hypocomplementemic paraneoplastic vasculitis: a rare case of B-cell malignancy.

Pemphigus foliaceus (PF) is a rare autoimmune blistering disease, occasionally associated with lymphoproliferative disorders. Urticarial vasculitis (UV) is classified as normocomplementemic or hypocomplementemic (HUV), the latter linked to systemic involvement and increased risk of malignancy. We present a rare case of atypical HUV syndrome in a 55-year-old female with a 24-year history of PF. She presented with recurrent heat, redness, and discoloration of the right hand. Examination revealed an erythematous-violaceous, edematous lesion with irregular but well-defined borders over the thenar region, without urticarial lesions. Laboratory evaluation showed marked hypocomplementemia (C3 0.73 g/L, C4 0.01 g/L), thrombocytopenia (32×10³/µL), leukocytosis, and positive ANA. Hepatomegaly was noted on systemic examination. Hematology consultation revealed a CD5-negative, CD19-positive B-cell lymphoproliferative disorder. Genetic testing excluded hereditary cancer mutations. This case underscores the clinical importance of recognizing atypical HUV presentations without urticaria and highlights the association of hypocomplementemia and thrombocytopenia with underlying hematologic malignancy. In patients with autoimmune background and cutaneous vasculitic lesions, hematologic malignancies should be considered, and thorough evaluation is essential to exclude paraneoplastic processes.