• Definition: Inflammatory infiltrate in the renal interstitium, often immune-mediated
• Causes:
o Drugs (most common):
Penicillins, cephalosporins, rifampicin
NSAIDs
Proton pump inhibitors (PPIs)
Allopurinol, sulfonamides
o Infections: streptococcal, leptospirosis, TB, CMV
o Systemic diseases: SLE, Sjögren’s, sarcoidosis
• Clinical Features:
o Fever, rash, arthralgia (classic triad, uncommon)
o AKI, sterile pyuria
o Eosinophilia ± eosinophiluria
• Diagnosis:
o Urine: WBCs, WBC casts, eosinophils
o Biopsy: interstitial oedema and inflammatory infiltrate (often lymphocytes, plasma cells, eosinophils)
• Management:
o Withdraw offending agent
o Corticosteroids if no improvement
o Monitor renal function — may progress to CKD if delayed
• Definition: Progressive interstitial fibrosis and tubular atrophy due to chronic injury
• Causes:
o Drugs/toxins:
Lithium (↓ concentrating ability, nephrogenic DI)
Analgesic nephropathy (NSAIDs ± paracetamol)
Heavy metals (lead, cadmium)
o Metabolic: hypercalcaemia, hyperuricaemia
o Infections: chronic pyelonephritis, TB
o Obstructive uropathy, reflux nephropathy
• Clinical Features:
o Polyuria/nocturia (due to tubular dysfunction)
o Non-nephrotic proteinuria
o Slowly progressive CKD
o Small, shrunken kidneys on imaging
• Diagnosis:
o Urinalysis: bland sediment, mild proteinuria
o Imaging: small echogenic kidneys
o Biopsy (if performed): interstitial fibrosis and tubular atrophy
• Management:
o Remove cause if possible
o Manage complications of CKD
o Avoid further nephrotoxins
• Definition: Ischaemic necrosis of renal papillae
• Causes (mnemonic: POSTCARDS):
o Pyelonephritis
o Obstruction of urinary tract
o Sickle cell disease/trait
o Tuberculosis
o Cirrhosis
o Analgesics (especially NSAIDs)
o Renal vein thrombosis
o Diabetes mellitus
o Systemic vasculitis
• Clinical Features:
o Flank pain, haematuria, pyuria
o May cause obstruction if sloughed papillae
• Diagnosis:
o CT urography or IVU: ring sign or filling defects
o Urine: necrotic tissue or clumps of cells
• Management:
o Treat underlying cause
o Supportive care; may require stenting if obstructive
• Pathophysiology:
o Non-caseating granulomas infiltrate interstitium
o Associated with hypercalcaemia (↑ 1α-hydroxylase activity in macrophages → ↑ vitamin D)
• Renal Manifestations:
o Hypercalcaemic nephropathy → nephrocalcinosis
o Granulomatous interstitial nephritis
o Nephrogenic diabetes insipidus
o Rarely glomerular disease (e.g. FSGS)
• Diagnosis:
o Elevated serum calcium, low PTH
o Imaging: nephrocalcinosis
o Renal biopsy: non-caseating granulomas
• Management:
o Corticosteroids first-line
o Treat hypercalcaemia (hydration, avoid vitamin D supplements)
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Author & Educational Disclaimer
Author:
Dr Phillip Cockrell BM FRCP DipClinEd
Dr Phillip Cockrell is a UK Consultant Physician in Internal Medicine, currently working at Queen Alexandra Hospital, Portsmouth University Hospitals NHS Trust. He has previously worked as a registrar across Intensive Care Medicine, Gastroenterology, Cardiology, Stroke Medicine, Acute Medicine, and Respiratory Medicine.
He has held senior leadership roles including Associate Clinical Director of the Acute Medical Unit, Clinical Director of Internal Medicine, and Chief of Medicine. Dr Cockrell has over 15 years’ experience in postgraduate medical education, having lectured extensively across the MRCP syllabus and contributed to MRCP revision teaching and course development.
Dr Cockrell holds a Bachelor of Medicine (BM), Fellowship of the Royal College of Physicians (FRCP), and a Diploma in Clinical Education (DipClinEd). His teaching approach is based on structured consolidation of complex medical topics to support efficient and effective revision for postgraduate examinations.
Purpose of this content:
The material on this page is intended solely for educational purposes to support revision for the MRCP (UK) Part 1 examination. It reflects examination-relevant principles of internal medicine and is designed to aid learning and pattern recognition.
Medical disclaimer:
This content is designed for postgraduate medical examination revision and does not constitute medical advice, diagnosis, or treatment guidance and must not be used as a substitute for professional clinical judgement, local guidelines, or specialist consultation. Clinical decisions should always be made in the context of individual patient circumstances and current national guidance.
