#3625 Navigating a diagnostic quandary of ANCA-associated vasculitis and Sweet's syndrome a case report

Abstract Introduction Sweet syndrome (SS), known as Acute febrile neutrophilic dermatosis is an uncommon condition. These dermatoses are often associated with systemic inflammatory disease and generally have a predilection in middle-aged women; however, the elderly may also be affected. It is characterised by an abrupt onset of painful skin lesions associated with variable systemic symptoms such as fever and elevated inflammatory markers. These skin lesions can persist for days and have a wide range of appearances, ranging from blisters or papules to ulcers. Specific treatment generally results in rapid improvement of symptoms within a few days, commonly without scarring. We describe a diagnostic dilemma in a patient with MPO-positive ANCA-associated vasculitis, presenting with clinical signs that closely mirrored Sweet's Syndrome. History A 71-year-old man who was recently diagnosed with MPO+Ve AAV with renal involvement for 3 months, presented to ED with fever and new skin lesions for 5–6 days. He was already on immunosuppression with Mycophenolate mofetil and a tapering dose of steroids. His baseline renal function was reasonable with an eGFR 45. He has an extensive past medical history that includes OSA, T2DM and Prostate cancer that was cured. On examination, there were discrete tender blisters across his upper chest, back and sides along with a few pockets of papulopustular lesions on his upper thighs and right lower leg. Day 1 Lab results revealed leucocytosis 14.8 × 103/ul with 77% neutrophils, CRP 68 mg/L and ESR 65 mm/H. The MPO-ANCA titres were downtrending at 17 IU/ml (70 IU at diagnosis). Procalcitonin levels were low (0.10 ng/ml) and ruled out bacterial infection. At certain areas, few lesions formed larger confluent ones. Dermatology team conducted 3 punch biopsies from 3 different sites for analysis. Meanwhile, the MMF was stopped at admission as it was suspected to be drug induced/active infection(pending lab confirmation) and steroids were resumed at a higher dose. Skin antibodies were negative for Bullous pemphigoid and Pemphigus vulgaris. The skin biopsy results revealed focal epidermal degeneration, with subepidermal vesiculation. A mixed subcorneal inflammatory infiltrate composed of neutrophils and other polymorphonuclear cells along with a tightly cuffed superficial and deep perivascular inflammatory infiltrate in the dermis were seen. Immunofluorescence studies showed subtle accentuation of the basement membrane zone, but was otherwise unremarkable. In conclusion, a report compatible with vasculitis was suggested based on clinical context, although histology was not typically suggestive The skin lesions began to improve significantly with the steroids and a diagnosis of atypical SS was considered. Towards the end of the admission, there was secondary skin infection that needed a short course of antibiotics. Discussion There are different histological types of SS described in literature : subcutaneous, eosinophilic, histocytoid and lymphocytic. The Von den Driesch criteria helps in the diagnosis of SS. The major crteria include abrupt onset of painful skin lesions along with histologic evidence of dense neutrophilic infiltrates without evidence of vasculitis. The minor criteria include fever, raised inflammatory markers (ESR,CRP) with neutrophilic leucocytosis along with an excellent response to treatment with systemic corticosteroids or potassium iodide. The criteria mandates 2/2 major criteria and 2/4 minor criteria to qualify for the SS diagnosis. Historically, the presence of vasculitis exclude classical SS. However, several newer reports have challenged this. There are emerging reports of AAVs associated with SS in small but promising numbers. Distinctive presentations, with several meeting the clinical criteria for SS have at times had evidence of vasculitis in biopsy samples. Certain common pathophysiological mechanisms such as neutrophil dysregulation could explain a possible overlap. Further clinical research and likely a revision of the criteria may be required to delineate between these two conditions.