Primary Sjögren’s Syndrome Presenting With Hypokalemic Rhabdomyolysis, Distal Renal Tubular Acidosis, and Fulminant Necrotizing Vasculitis: A Case Report

Primary Sjögren's syndrome (pSS) is a systemic autoimmune disease characterized by exocrine gland dysfunction and heterogeneous extraglandular manifestations. Renal involvement, most frequently distal renal tubular acidosis (dRTA), may present with severe metabolic disturbances. Rhabdomyolysis due to hypokalemia and systemic vasculitis are uncommon but potentially life-threatening complications. We report a 36-year-old woman who presented with fever, profuse diarrhea, progressive proximal muscle weakness, and a 10-kg weight loss. Laboratory evaluation revealed profound hypokalemia, hyperchloremic non-anion gap metabolic acidosis consistent with dRTA, and rhabdomyolysis with creatine phosphokinase (CPK) of 42,000 U/L. Electromyoneurography (EMNG) confirmed inflammatory myopathy, while autoimmune serology was positive for antinuclear antibody (ANA), anti-Ro52, anti-SSA, and anti-proliferating cell nuclear antigen (PCNA) with marked hypocomplementemia. Despite supportive therapy, she developed an acute abdomen. Emergency laparotomy revealed perforated ischemic colitis and gangrenous cholecystitis. Histopathology confirmed necrotizing vasculitis of small- and medium-sized arteries. Treatment included continuous renal replacement therapy (RRT) with cytokine hemoadsorption. After surgical stabilization and histopathological confirmation of necrotizing vasculitis, immunosuppressive therapy was initiated according to the European League Against Rheumatism (EULAR) and Kidney Disease: Improving Global Outcomes (KDIGO) recommendations for the management of severe systemic vasculitis with visceral involvement. The patient received intravenous pulse cyclophosphamide (CYC) at a dose of 800 mg (corresponding to a total induction dose of approximately 2.5-3 g (as recommended for remission induction), combined with high-dose methylprednisolone with gradual tapering. Supportive measures included intravenous hydration, Mesna uroprotection, and antiemetic prophylaxis. The patient showed significant clinical improvement, normalization of electrolyte and laboratory parameters, and functional recovery within two weeks. This case underscores two severe extraglandular phenotypes of pSS: dRTA-induced hypokalemic rhabdomyolysis and fulminant systemic necrotizing vasculitis. Both are rarely reported and carry high morbidity and mortality. Recognition of hypokalemia as a potential trigger for rhabdomyolysis and vigilance for vasculitic complications are crucial for timely diagnosis. Multidisciplinary management, including nephrology, immunology, surgery, and aggressive immunosuppression, proved life-saving. pSS may present with atypical and catastrophic extraglandular involvement. Physicians should maintain a high index of suspicion when encountering metabolic disturbances with multisystem features. Early recognition and coordinated intervention can significantly improve outcomes.