Tubulointerstitial Disease — Written Clinical Reasoning

Model answer — Part A: the PPI creatinine drift

Diagnostic reasoning. Frame it aloud: unexplained subacute AKI with sterile pyuria, modest proteinuria and normal-sized kidneys, four months into a new drug, is acute interstitial nephritis until proven otherwise — and the absence of rash, fever and eosinophilia is the expected modern presentation, not evidence against it ^[1]. PPIs are a leading culprit precisely because their latency is months and their course is silent; the nationwide case-control data put a severalfold increased risk on current users ^[5]. State what would refine the probability: the creatinine timeline against the drug chart, white-cell casts on urine microscopy, and exclusion of pre-renal, obstructive and glomerular causes ^[1]. Name the limits of eosinophiluria if asked — poor sensitivity and specificity, so it steers nothing on its own ^[3].

Immediate management. Stop the omeprazole today — withdrawal is the one intervention with consistent outcome data, and delay in withdrawal tracks with worse recovery ^[2]. Document the adverse drug reaction, reconcile the rest of the chart (amlodipine, atorvastatin and metformin are not AIN culprits — keep them, but review need), avoid further nephrotoxins, and monitor potassium, acidosis and urine output ^[1].

Steroids and deprescribing. Biopsy if the creatinine does not begin recovering after withdrawal, if it worsens, or before committing to steroids — biopsy is the only definitive test and grades the fibrosis that predicts recovery ^[3]. On steroids, give the examinable synthesis: the evidence is retrospective, benefit concentrates in early, biopsy-proven, significant AKI without contraindication, and a typical regimen is prednisone about 1 mg/kg with a taper over 8–12 weeks — offered as a shared decision in a patient of his age and comorbidity ^{[2] [6]}. Close with deprescribing: the PPI needs a genuine indication review and a non-PPI alternative if acid suppression is truly required, because casual re-prescription is how AIN recurs ^[5].