A Tale of Overlapping Autoimmune Serologies: Diagnosing Hydralazine-Induced Antineutrophilic Cytoplasmic Antibody (ANCA)-Associated Vasculitis (AAV) Related With Isolated Pulmonary Involvement.

Hydralazine is an antihypertensive that can induce immune-related adverse effects, such as hydralazine-induced lupus and hydralazine-induced antineutrophilic cytoplasmic antibody (ANCA)-associated vasculitis (AAV). AAV involves necrotizing inflammation of small blood vessels, manifesting as fever, malaise, arthralgia, and myalgia, potentially leading to organ failure. Diagnosis includes clinical evaluation, serological testing for ANCA, and histopathological examination, confirmed by necrotizing granulomatous inflammation in affected tissues. This case report presents a rare presentation of hydralazine-induced AAV limited to the lungs, with isolated pleural involvement. A 57-year-old Caucasian male with hypertension, severe diastolic dysfunction, and end-stage renal disease undergoing dialysis presented with dyspnea, cough, and fatigue. Examination revealed bilateral lung crackles and peripheral edema. Chest computed tomography (CT) revealed a pleural effusion. Despite dialysis and thoracentesis, the patient showed no improvement, leading to pleural fluid analysis, which revealed an exudative pattern with reactive mesothelial cells. An autoimmune workup revealed elevated levels of antinuclear antibodies (ANA), anti-dsDNA, anti-histones, and ANCA. This presents a diagnostic dilemma: evolving systemic lupus erythematosus (SLE) or drug-induced vasculitis. Studies have highlighted that ANCA-positive patients may display serological features that overlap with SLE. Using the 2019 American College of Rheumatology (ACR) SLE criteria and biopsy results, we ruled out certain conditions and ultimately diagnosed the patient with chronic hydralazine-induced AAV. The patient's condition improved after hydralazine discontinuation and initiation of corticosteroid therapy. Pleural effusion can be an initial sign of AAV, and clinicians should be vigilant, especially in patients with end-stage renal disease who are unresponsive to dialysis.