Microscopic polyangiitis and systemic lupus erythematosus overlap syndrome; an unusual presentation

Lupus nephritis (LN) is characterized by glomerular immune-complex deposits usually in a full house (FH) pattern. In contrast, ANCA-associated glomerulonephritis (GN) is typically pauci-immune GN. Patients fulfilling both systemic lupus erythematosus (SLE) and ANCAassociated vasculitis (AAV) classification criteria defining "SLE/AAV overlap syndrome" have been rarely reported. However, FH nephropathy (FHN) without overt SLE at presentation is described and considering an overlap syndrome in this situation is challenging. A 40-year-old man presented to the emergency because of hemoptysis and macroscopic haematuria. We found acute kidney injury (plasma creatinine 5.16 mg/dL, N: 0.72- 1.17) with an active urinary sediment (proteinuria 3+, haematuria 3+). Chest computerized tomography showed intra-alveolar diffuse haemorrhage confirming pulmonary-renal syndrome. High titers of anti-MPO ANCA in the absence of ANA strongly correlated with microscopic polyangiitis. Kidney biopsy confirmed crescentic GN, however FH immunofluorescence (IF) pattern suggested a LN (class IV). Despite plasma exchanges associated to steroids and rituximab, kidney function declined and haemodialysis was initiated. During 12 months of follow-up on azathioprine-low dose steroids treatment, he remains still asymptomatic. However, considering the appearance of antinuclear antibodies (ANA), presence of antiphospholipid antibodies and low complement level, we considered the diagnosis of SLE/AAV overlap syndrome. SLE/AAV overlap syndrome is a very rare condition and has a very poor kidney function outcome. We underline that the patients with AAV and FHN require a regular screening for clinical and biological SLE criteria, even in their absence at initial presentation as it could develop later.