Antineutrophil cytoplasmic antibody related vasculitis with a unique imaging presentation of organizing pneumonia. The key role of lung ultrasound

Introduction: Neutrophil cytoplasmic antibody (ANCA)-related vasculitis (AAV) is characterized by necrotizing inflammation of small and medium-sized arteries. This heterogeneous group of vasculitides, including microscopic polyangiitis (MPA), granulomatosis with polyangiitis (GPA) and eosinophilic granulomatosis with polyangiitis (EGPA), further classified according to two distinct types of ANCA pattern, cytoplasmic ANCA (c) and perinuclear ANCA (p), mainly directed against proteinase 3 (PR3) and myeloperoxidase (MPO), respectively. The most frequent pulmonary imaging finding is honeycombing, typical of the usual interstitial pneumonia (UIP) pattern, particularly in AAV MPO-ANCA positive patients. Another pattern, although rare, is represented by organizing pneumonia (OP). The efficacy and reliability of lung ultrasound (LUS) is very good in connective tissue diseases, especially interstitial pulmonary fibrosis (ILD). Subpleural infiltrates on ultrasound are visualized as round or oval hypoechoic consolidations, without visible central flow in color Doppler and power Doppler modes. Case presentation: We report a case of a 25-year-old woman who admitted to our hospital with fever (38°C), dyspnea and pleuritic chest pain. The medical history was positive for Hashimoto’s thyroiditis. Laboratory tests showed elevated inflammatory markers, no evidence of respiratory failure. LUS revealed bilateral and multiple pulmonary consolidations with a rounded and anechoic appearance. We performed computed tomography (CT) which showed multiple bilateral peripheral and non-segmental peri-bronchovascular consolidations with air bronchogram, which corresponds to the OP pattern. Over the next three days, LUS monitoring revealed a rapid expansion in the size and number of consolidations. Transthoracic biopsy revealed a histopathological picture attributable to vasculitis. ANCA antibody determinations were positive for anti-PR3 ANCA antibodies (213 AU/ml), MPO-ANCA antibodies were negative. The consolidations showed a clear improvement after the start of cortisone therapy 1 mg/kg i.v., subsequently followed by Rituximab (RTX) 1 g i.v. Conclusion: There is emerging evidence to support that PR3-ANCA and MPO-ANCA antibodies have the potential to stratify patients into unique phenotypic subgroups. LUS allows also a multiple reassessments to monitor the response to therapy. In this case report in particular, LUS played a decisive role in the diagnostic steps, accelerating the achievement of the definitive diagnosis, thanks to the OP-like pattern which extended to involve the pleura.