Renal tuberculosis usually results from hematogenous spread and is an underdiagnosed entity. Up to 20% of patients with extrapulmonary tuberculosis have urogenital involvement, of which the kidney is most commonly affected. Its classic manifestation is the presence of microscopic pyuria without bacterial growth on urine culture—or “sterile pyuria.” More often, other bacteria are also present, and microscopic hematuria may coexist. Urine cultures were once the gold standard for diagnosis, but the advent of urine nucleic acid testing for tuberculosis has increased sensitivity. Characteristic findings on imaging include papillary necrosis and cavitation of the renal parenchyma. Ureteral strictures or calcifications may also be present. Kidney biopsy is not usually needed to confirm the diagnosis but reveals granulomatous inflammation and tubulointerstitial nephritis. Prompt initiation of antituberculosis treatment is indicated, without which progression to ESKD is common due to chronic inflammation and obstruction.
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