PA39 A rare case of <i>Streptococcus</i>-induced cutaneous polyarteritis nodosa

Abstract A 17-year-old boy presented with a 10-month history of a painful, firm nodule on the right foot, preceded by fever, sore throat and cervical lymphadenopathy, approximately 3 weeks after returning from a safari holiday. Prior to his presentation, he was treated with doxycycline for the sore throat and had a short course of prednisolone for the swelling, which helped his symptoms. However, the symptoms reoccurred after completing the course. Blood tests showed an elevated anti-streptolysin O (ASO) titre of 200. But serological tests were all negative for hepatitis B, hepatitis C, HIV, antinuclear antibody, extractable nuclear antigens, antineutrophil cytoplasmic antibodies, complements, immunoglobulins, lupus anticoagulants, lupus anticoagulant and cardiolipin. An ultrasound of the right foot showed soft-tissue swelling and increased vascularity, with thickening of the superficial vessel suggestive of phlebitis. A punch biopsy from the right foot revealed necrotizing inflammation of medium-sized vessels in the deep dermis extending into the subcutaneous fat with mixed inflammatory infiltrates. We made an initial diagnosis of necrotizing venulitis. However, a review of the histology findings supported poly­arteritis nodosa (PAN). In view of this and a positive ASO titre, a diagnosis of Streptococcus-induced cutaneous PAN was made. Cutaneous PAN (C-PAN) is a rare form of cutaneous vasculitis that involves small- and medium-sized arteries of the dermis and subcutaneous tissue without systemic involvement (Subbanna PKA, Singh NV, Swaminathan RP. Cutaneous polyarteritis nodosa: a rare isolated cutaneous vasculitis. Indian Dermatol Online J 2012; 3: 21–4; Fathalla BM, Miller L, Brady S, Schaller JG. Cutaneous polyarteritis nodosa in children. J Am Acad Dermatol 2005; 53: 724–8). It is commonly triggered by infections, which include but are not limited to group A Streptococcus, hepatitis B, hepatitis C and HIV. It presents with tender subcutaneous nodules, digital gangrene, livedo reticularis and subcutaneous ulcerations. The diagnosis is by skin biopsy, and characteristic pathological features of necrotizing vasculitis of small-to-medium-sized arterioles of the dermis and subcutis are seen. Management involves the use of corticosteroids and antibiotics to address the underlying streptococcal infection if it has not already been treated. This case highlights the importance of considering C-PAN in the differential diagnosis of painful cutaneous nodules, especially in the context of a prior streptococcal infection.