PA27.8-10 | Tubulointerstitial Diseases, ATN & Pyelonephritis — Summary & Reflection

REFLECT

Think about the 58-year-old diabetic man from the hook. He had contrast-induced nephrotoxic ATN triggered by the angiogram PLUS ascending pyelonephritis (fever, WBC casts). His diabetes contributed to both: impaired tubular regeneration worsens ATN prognosis, and impaired neutrophil function + glycosuria predisposed him to infection.

Now consider: if this patient is not treated aggressively, which complication is he most at risk for, and why? Write a 3-sentence answer identifying the complication, the pathological mechanism, and the clinical sign that would alert you to it. Compare your answer with the teaching pearl in your PBL session.

KEY TAKEAWAYS

Tubulointerstitial Diseases — Core Take-Aways:

1. Classification — six categories: ischaemic, toxic, infective, immune/allergic, metabolic, obstructive. The cause determines the cell type and distribution of injury.

1. ATN pathogenesis — four mechanisms: tubular cell death → cast obstruction → backleak → vasoconstriction. All four reduce GFR synergistically.

1. ATN morphology — granular (muddy-brown) casts; patchy necrosis (ischaemic) vs. diffuse PCT necrosis (nephrotoxic); tubulorrhexis in ischaemic ATN; no significant inflammation.

1. Three phases — initiation (subtle) → maintenance/oliguric (↑K⁺, ↑creatinine, ≤400 mL urine/day) → recovery/polyuric (regeneration, ↓K⁺). ATN is fully reversible if insult removed.

1. Acute pyelonephritis — ascending E. coli commonest; predisposed by VUR, obstruction, DM; WBC casts prove parenchymal involvement; complications — papillary necrosis (diabetics), pyonephrosis, perinephric abscess.

1. Chronic pyelonephritis — coarse polar scars + calyceal blunting; thyroidisation hallmark on histology; reflux nephropathy = commonest form.

1. Drug-induced TIN — eosinophils + lymphocytes; reversible on drug withdrawal; distinguish from ATN by allergy triad and absence of granular casts.

1. Papillary necrosis — POSTCARDS mnemonic; DM + pyelonephritis = highest risk; filling defect on IVU/CT urogram.