Abstract Title Microscopic Polyangiitis and the Impact of Steroid Treatment on Lung Compliance

Background Microscopic polyangiitis (MPA) is a small-vessel vasculitis characterized by systemic infiltration, primarily targeting the renal and pulmonary systems. While diffuse alveolar hemorrhage (DAH) is among its most lethal pulmonary manifestations, the spectrum of lung pathology in MPA is extensive, necessitating immediate immunosuppressive therapy. Our case study focuses on an elderly woman who initially presents with MPA-induced rapid progressive glomerulonephritis (RPGN) but subsequently develops an array of vasculitis-related pulmonary insults requiring endotracheal intubation. Following a brief course of immunosuppression, her lungs demonstrate rapid physiologic recovery. This case highlights the role of induction therapy with steroids in enhancing lung compliance, leading to a more profound respiratory recovery in MPA patients without DAH-related pulmonary symptoms.

Case Presentation The patient, a woman in her mid-60s with a history of hypertension, chronic anemia, and Raynaud’s phenomenon, was referred to the emergency department by her primary care provider for a creatinine level of 16.53 and potassium level of 6.3. Immediate hemodialysis was initiated, and an autoimmune workup for acute renal failure was conducted. Labs and renal biopsy revealed RPGN induced by MPA. Within two weeks, the patient's oxygen demand increased, and clinical presentation and imaging raised concerns for DAH, leading to intubation. A subsequent bronchoscopy and bronchoalveolar lavage showed no active hemorrhage. Induction therapy with two days of pulse-dose steroids (methylprednisolone MTP) followed by five days of low-dose steroids was initiated. The patient's ventilator settings rapidly improved post-MTP therapy, with decreased pressure support and FiO2 requirements. She was extubated within a week and discharged on MTP and rituximab.

Discussion This case features an uncharacteristic pulmonary presentation of MPA, marked by acute hypoxemic respiratory failure not due to DAH but due to various small-vessel disease components. The patient's rapid recovery post-MTP induction was objectively measured through improved markers of lung compliance, including reduced daily driving pressures, decreased peak pressures, and increased dynamic compliance. These findings suggest that current guidelines for induction therapy with steroids could benefit pulmonary MPA patients without DAH, especially in ventilated patients, by improving lung compliance.