Acute Tubulointerstitial Nephritis (ATIN) in Patient With Autosomal Dominant Polycystic Kidney Disease (ADPKD): A Case Report.

Background: Autosomal dominant polycystic kidney disease (ADPKD) is characterized by diffuse renal cysts that secrete cytokines, which induce interstitial inflammation and fibrosis. Meanwhile, acute tubulointerstitial nephritis (ATIN) is characterized by inflammatory infiltrates in the interstitium, where kidney biopsy remains the mainstay for diagnosis. Case Presentation: An 85-year-old male complained of fatigue, loss of appetite, and low-grade fever for a week. Within the past month, the patient received ciprofloxacin for a urinary tract infection (UTI) and described flu symptoms. The medical history consisted of ADPKD type 2 with baseline serum creatinine (sCr) at 1.2 mg/dL. Labs showed acute kidney injury (AKI) (sCr = 3.98 mg/dL). The combination of previous drug and infection exposure, systemic symptoms, and AKI suggested the diagnosis of ATIN. The kidney function and clinical status improved with corticosteroids (CS) treatment, where sCr returned to 2.4 mg/dL. Unfortunately, the patient died due to severe community-acquired pneumonia. Conclusion: This case highlighted the dilemma of ATIN diagnosis in a patient with ADPKD and presents the first case of ATIN in ADPKD patients. Kidney biopsy was unable to be performed for ATIN diagnosis in this ADPKD patient due to diffuse renal cysts. Also, the biopsy could be confused by interstitial fibrosis and infiltrates that appeared early in ADPKD biopsies. Clinicians could suggest an ATIN diagnosis and start treatment based on the combination of new-onset AKI aligned with clinical history and laboratory tests in such ADPKD patients. Also, the improvement of kidney function after CS treatment could support the ATIN diagnosis.