Abstract Introduction Pulmonary fibrosis often precedes systemic vasculitis and usually indicates a worse prognosis. Here-in we present a unique case of how an incidental finding of an elevated creatinine led to the unmasking of systemic vasculitis. Case Presentation A 66-year-old woman with a history of hypertension, inflammatory polyarthropathy, and interstitial lung disease (ILD) presented to National Jewish Health (NJH) for a second opinion regarding her ILD diagnosis. She was known to have low-titer myeloperoxidase (MPO)-antineutrophil cytoplasmic antibodies (ANCA) and was antineutrophil antibody positive. The patient had been taking azathioprine 50 mg daily but discontinued the medication two weeks prior to presentation due to worsening abdominal discomfort. During her evaluation at NJH, routine laboratory testing revealed an elevated creatinine of 4.48 mg/dL, and she was subsequently admitted to the hospital for further evaluation of acute kidney injury. Her baseline renal function had been mildly reduced (creatinine ≈ 1.8 mg/dL), and a prior kidney biopsy had shown acute tubular necrosis without immune complex deposition. During her hospitalization, a repeat kidney biopsy was performed due to concern for acute glomerulonephritis. Pathology demonstrated necrotizing and crescentic glomerulonephritis, with six of fourteen glomeruli showing active crescents and minimal immune deposits on immunofluorescence. She was diagnosed with MPO-ANCA-associated microscopic polyangiitis (MPA). She was started on pulse-dose intravenous methylprednisolone followed by oral prednisone per the PEXIVAS protocol. Rituximab was initiated, with a second dose planned for day fourteen. She was not restarted on her azathioprine. Following treatment, her creatinine improved to approximately 3 mg/dL. She was discharged with a prednisone taper and close nephrology follow-up. Discussion This case highlights the complex association between MPO-ANCA vasculitis and ILD. Up to 4% of patients who are MPO positive at ILD diagnosis have no clinical features of microscopic polyangiitis (MPA), while 5.7% of those initially diagnosed with idiopathic pulmonary fibrosis (IPF) later develop MPO antibodies, many progressing to systemic vasculitis (1). In this case, withdrawal of low-dose azathioprine likely unmasked an MPA flare, consistent with the known risk of relapse following cessation of maintenance immunosuppression in ANCA-associated vasculitis. Determining which ANCA-positive patients with ILD but no other systemic manifestations of vasculitis require ongoing systemic immunosuppression remains challenging. We suggest patients with ILD who are MPO-antibody positive may benefit from continued or full-dose immunosuppression, with close monitoring if therapy must be reduced or discontinued. References 1. Kagiyama N, Takayanagi N, Kanauchi T, et al. BMJ Open Respir Res. 2015;2:e000058. This abstract is funded by: None
Newsom et al. (Fri,) studied this question.