Acute tubulointerstitial nephritis in a patient with early bronchial tuberculosis

Patients with chronic kidney disease (CKD) are commonly at high risk of tuberculosis (TB). Conversely, TB rarely causes tubulointerstitial nephritis. A 75-year-old Japanese man who was undergoing periodic follow-ups for CKD stage G3aA3 with membranous nephropathy was diagnosed with acute kidney injury (AKI) (estimated glomerular filtration rate [eGFR]: 15 mL/min/1.73 m²) without prerenal AKI. He reported developing recent-onset cough 3 weeks prior to presenting to us. Renal biopsy revealed acute tubulointerstitial nephritis along with known membranous nephropathy. CD4⁺ helper T cells comprised most lymphocytes in the tubulointerstitium. Results of the interferon-gamma release assay, sputum smear test, polymerase chain reaction (PCR), and culture test were positive for TB. Chest computed tomography revealed thickening of the left bronchial wall; therefore, a diagnosis of early bronchial TB was made; his urine culture and PCR were negative for TB. At four months after TB treatment with no immunosuppressive therapy, his eGFR improved to 50 mL/min/1.73 m², and based on this progress, the AKI was diagnosed as tuberculosis-associated tubulointerstitial nephritis (TATIN). Although TATIN typically occurs with chronic or miliary tuberculosis, it is very rare in early bronchial TB. Identification of TATIN is important in kidney diseases of unknown etiology, and treatment with anti-TB drugs is necessary.