Microscopic polyangiitis (MPA) is a systemic vasculitis characterized by small vessel involvement. Studies suggest MPO-ANCA is involved in its pathogenesis, and the titer may reflect disease activity. Generally, MPA is not associated with pregnancy. Isolated case reports have only noted neonatal cutaneous vasculitis. We report a unique case of transplacental transfer of MPO-ANCA from mother to 32-week gestational age neonate resulting in neonatal pulmonary hemorrhage and renal involvement that was successfully treated.

We obtained MPO-ANCA titers from the cord blood and neonate on day of life (DOL) 8, 15, and 25. Corresponding neonatal and maternal labs were obtained, including: ANCA, ESR, CRP, ANA, serial UA, CBC, metabolic panels, and chest x-rays.

The neonate was delivered by C-section secondary to maternal pre-eclampsia and dyspnea. Prior to delivery, the mother received 2 doses of betamethasone. Neonatal chest x-ray on DOL 1 showed bilateral pulmonary infiltrates, and she was intubated. Initial UA showed proteinuria and hematuria. The MPO-ANCA titer was 3.30 in the cord blood and 2.5 in the mother. Acute pulmonary hemorrhage developed DOL 3, and the neonate was infused hydrocortisone 3 mg/kg. Persistence of the MPO-ANCA and concern of cardiac septal hypertrophy secondary to prolonged steroid therapy led to neonatal exchange transfusion on DOL 5. With the therapeutic interventions and progressive reduction of the MPO-ANCA titer, neonatal pulmonary-renal symptoms resolved.

Animal studies suggest MPO-ANCA contributes to vascular damage. Our patient represents an in vivo case of MPO-ANCA transfer and pulmonary-renal pathogenicity that was successfully treated with steroids and exchange transfusion.