Tubulointerstitial Disease — DCE Clinical Case

Reading the data — what each piece contributes

• Urine microscopy: sterile pyuria with white-cell casts localises inflammation to the renal tubulointerstitium — the most telling bedside clue in AIN — while modest sub-nephrotic proteinuria fits a tubular rather than glomerular process [1] [2].
• Urinary eosinophils at 3%: supportive but weak. The test performs poorly as a discriminator — eosinophiluria occurs in cystitis, pyelonephritis and other AKI causes, and biopsy-proven series show limited sensitivity and specificity — so it raises probability without deciding anything [2] [3].
• The drug chart: two plausible culprits with different signatures. The amoxicillin course (completed six weeks ago) fits the classic antibiotic latency of days to weeks; the pantoprazole (seven months) fits the PPI pattern — long silent latency, no allergic features, discovered late [4] [1]. Ibuprofen PRN is a third possibility and the one class that can add nephrotic-range proteinuria — his 0.7 g/day argues against a dominant NSAID lesion [1].
• Normal ultrasound and absent triad: normal kidney size supports an acute process; the missing rash, fever and eosinophilia exclude nothing — the full triad appears in only a small minority of modern drug-induced AIN [2].

Presentation template (deliver this to the examiner)

"Mr Ngata is a 69-year-old man with subacute AKI whose data unify as acute interstitial nephritis: sterile pyuria with white-cell casts, modest proteinuria, normal-sized kidneys, and two recent culprit-class exposures — a completed amoxicillin course six weeks ago and seven months of pantoprazole. The absence of allergic features does not argue against the diagnosis. My priorities are to stop both culprit agents, reconcile the chart, biopsy to confirm and grade chronicity given the significant AKI, and make an explicit, shared decision about early corticosteroids." [2] [4] [5]

Management — what you will actually do

1. Stop the culprits today — both pantoprazole and any further beta-lactam exposure from the same class pending assessment; withdrawal timing is associated with renal recovery, so this is not a decision to defer [5].
2. Reconcile and protect — document adverse drug reactions, hold PRN ibuprofen while the AKI settles, keep metoprolol and the multivitamin (not AIN culprits), and avoid further nephrotoxins including contrast where possible [1].
3. Biopsy — his AKI is significant, two culprits are plausible, and steroids are on the table: biopsy confirms the diagnosis, does not distinguish the culprit but grades fibrosis, and excludes granulomatous or IgG4-related mimics [2] [1].
4. Steroid decision — if biopsy shows active inflammation without advanced fibrosis, offer prednisone about 1 mg/kg with an 8–12 week taper, framed on retrospective evidence favouring early treatment, and decided with the patient [5].
5. Follow the recovery — creatinine through the arc over weeks, CKD surveillance if function plateaus below baseline, and clear documentation that PPIs and implicated beta-lactams must not be casually restarted [4] [5].

Probing questions

"Two culprit drugs — which do you blame?" — "I stop both and say so. The amoxicillin fits classic antibiotic latency; the pantoprazole fits the silent PPI pattern, which the epidemiology now identifies as a leading cause. Biopsy will not separate them and management does not wait for the answer — both are withdrawn, both are documented, and neither is rechallenged." [4] [5]

"The urinary eosinophils were only 3%. Does that weaken the diagnosis?" — "No — the test is too weak to carry weight in either direction. Biopsy-proven series show urinary eosinophils discriminate poorly between AIN and other kidney disease, and the original description defined eosinophiluria across a broad clinical spectrum. The white-cell casts, sterile pyuria, drug timeline and biopsy are what I stand on." [2] [3]

"Would you have biopsied if the creatinine had fallen after withdrawal?" — "That is the legitimate conservative path: a clear culprit, mild AKI, and prompt recovery after withdrawal can be managed without histology. My biopsy triggers are significant or worsening AKI, no identifiable culprit, failure to recover after withdrawal, nephrotic-range proteinuria, or a suspected systemic cause — his case meets the first and arguably the third." [1] [2]