Recurrent Infection-Triggered Immune Thrombocytopenia Flares in Medullary Sponge Kidney: A Case Report

Medullary sponge kidney (MSK) is a congenital collecting duct abnormality associated with nephrocalcinosis, recurrent nephrolithiasis, hematuria, urinary tract infections, and obstructive urological complications. Immune thrombocytopenia (ITP) is an acquired autoimmune disorder characterized by isolated thrombocytopenia and bleeding risk. We report a case illustrating how these two chronic conditions can interact indirectly to create a recurrent management dilemma. A 45-year-old woman with bilateral MSK and chronic ITP controlled with weekly romiplostim had a baseline platelet count of approximately 120-130 × 10³/µL. Over several months, she experienced recurrent urological events, including obstructive nephropathy, extended-spectrum beta-lactamase (ESBL) urosepsis, pyelonephritis, ureteritis, and repeated ureteral stenting. During a March 2026 admission for right pyelonephritis with bilateral stents, her platelet count fell abruptly from approximately 120 × 10³/µL to 7 × 10³/µL, accompanied by gross hematuria, and improved after intravenous immunoglobulin and dexamethasone. She presented again in April 2026 with left flank pain, nausea, gross hematuria, leukocytosis, positive urinalysis, bilateral ureteral wall thickening, periureteral stranding, mild left hydronephrosis, and bilateral medullary calcifications consistent with MSK. Her platelet count had again declined to 27 × 10³/µL. Workup did not support thrombotic microangiopathy, disseminated intravascular coagulation, pseudothrombocytopenia, drug-induced thrombocytopenia, hemolysis, viral infection, or renal failure as alternative causes. She was treated with meropenem, fluconazole, hydration, analgesia, and intravenous immunoglobulin, while corticosteroids were deferred because of active infection and romiplostim was held. Platelets rose to 116-125 × 10³/µL within 48 hours, with resolution of hematuria and clinical improvement. This case emphasizes that recurrent MSK-related urinary infections may precipitate clinically significant ITP flares. Early platelet monitoring and coordinated hematology, infectious disease, and urology input are essential when infection control, bleeding risk, and procedural decisions overlap.