A Case of Isolated Autoimmune Ureteritis in A 25-Year-Old Male.

Background: Ureteritis is an inflammatory condition of the ureters, most commonly caused by infection, often associated with cystitis or pyelonephritis. Non-infectious causes, including autoimmune diseases, are rare and pose significant diagnostic challenges. Autoimmune ureteritis is an exceedingly rare entity with limited literature guidance, often diagnosed by exclusion. Case description: We report the complex six-year clinical course of a 25-year-old male who initially presented with right flank pain and macroscopic haematuria. Early investigations including imaging and cystoscopy were unremarkable, leading to a provisional diagnosis of loin pain haematuria syndrome. Two years later, worsening symptoms prompted repeat imaging, which revealed bilateral ureteric and renal pelvic thickening. Multiple investigations, including extensive infectious screening, PET-CT and serial ureteroscopies with biopsies, failed to identify a definitive cause. Histopathology remained non-diagnostic; empirical antibiotic therapy was ineffective. A trial of corticosteroids resulted in significant symptom improvement and radiological resolution of inflammation, strongly suggesting an autoimmune aetiology. Immunosuppressive therapy with mycophenolate mofetil, later switched to azathioprine, maintained remission. The patient remains in remission, having finished a two-year course of azathioprine. Conclusion: This case highlights the diagnostic complexity of autoimmune ureteritis, particularly in the absence of systemic autoimmune disease. The diagnosis was made by exclusion after thorough investigation ruled out infection, malignancy and systemic autoimmune conditions. The patient's positive response to immunosuppression supports an immune-mediated pathogenesis. Isolated autoimmune ureteritis should be considered in patients with persistent ureteric inflammation, and negative infectious and malignant work-up. Early recognition and immunosuppressive therapy may prevent long-term structural damage and preserve renal function. LEARNING POINTS: This case demonstrates the diagnostic complexity of isolated autoimmune ureteritis, highlighting the value of excluding the common differentials.It highlights the limitations of diagnostic tools in ureteric disease, reinforcing the role of clinical judgement and treatment trials when histology is inconclusive.It illustrates the role of immunosuppressive therapy in rare inflammatory conditions, not only as an effective treatment but also as a diagnostic tool.