A Pulmonary Presentation of Microscopic Polyangiitis: From Missed Diagnosis to Accurate Empiric Treatment

Abstract

INTRODUCTION: Microscopic polyangiitis (MPA) is an idiopathic systemic antineutrophil cytoplasmic autoantibodies associated vasculitis (ANCA-AV) affecting small blood vessels. MPA most prominently affects the lungs (25-55%) and kidneys (80-100%). Diagnosis is based on clinical manifestations, ANCA detection, pulmonary imaging, and confirmatory renal/ pulmonary biopsies. Treatment centers around remission induction with corticosteroids and maintenance with immunomodulators(1). We present a case where a presumptive diagnosis was successfully used to initiate treatment of pulmonary hemorrhage in MPA. CASE PRESENTATION: A 50 yo female with a history of HTN presented with 3 months of cough and progressive dyspnea refractory to an outpatient course of azithromycin. On initial presentation, she was found to have bilateral rales and pedal edema on exam. Labs revealed BUN 48; SCr 1.98, prompting a workup for CHF and AKI. She also noted arthralgias, and autoimmune serologies were ordered upon discharge. She returned 3 weeks later with new onset hemoptysis and worsening SOB. She was tachycardic with diffuse wheezing and rales on exam. CT chest was remarkable for bronchiectasis and centrilobular nodules coalescing into a consolidative mass. Aforementioned serologies were significant for ESR > 120, CRP 86.40, RF 189, ANCA positive with MPO >800, p-ANCA 1:160. Infectious workup notable for 3 AFB smears, were negative. A VATS was planned prior to treatment, however, due to clinical deterioration and high suspicion for vasculitis, empiric pulse dose steroids were initiated with almost immediate improvement of her symptoms. Subsequent lung wedge biopsy revealed diffuse alveolar hemorrhage with neutrophilic capillaritis consistent with microscopic polyangiitis. She continued to improve and received a loading dose of Rituximab with plans for continued administration as an outpatient. DISCUSSION: MPA is an ANCA-AV with the potential to affect multiple organ systems. Common pulmonary manifestations include: diffuse alveolar hemorrhage from pulmonary capillaritis, associated with hemoptysis, dyspnea, cough, and pleuritic chest pain. Although histological confirmation is the gold standard for diagnosis, when there is high pretest probability, empiric treatment is warranted(1). This approach is also favorable when patients cannot tolerate or refuse the necessary diagnostic procedure. The failure of outpatient antibiotics, negative infectious workup, positive autoimmune serologies, and suggestive imaging in the setting of continued progression allowed us to have a high clinical suspicion for vasculitis related pulmonary hemorrhage. This facilitated timely treatment and clinical improvement while awaiting confirmatory biopsies. CONCLUSIONS: In summary, if the clinical picture is highly suspicious for ANCA-AV, one can empirically treat with corticosteroid therapy while awaiting definitive diagnostic biopsy.