Renal Papillary Necrosis

Renal papillary necrosis is ischaemic necrosis of the renal papillae (the distal medullary pyramids). The papillae are vulnerable because they have a precarious end arterial blood supply (vasa recta) and a hypertonic environment.

Necrosis may be partial or complete and unilateral or bilateral. Sloughed papillae can cause ureteral obstruction (colic).

Causes and risk factors are summarised by the mnemonic POSTCARDS:

• Pyelonephritis (especially in diabetes and obstruction)
• Obstruction of the urinary tract
• Sickle cell disease and trait (hypoxic medullary environment)
• Tuberculosis
• Cirrhosis of the liver
• Analgesic nephropathy: long term, high dose combined analgesics such as aspirin or paracetamol with phenacetin and caffeine, and non-steroidal anti-inflammatory drugs; typical cumulative dose above 3 kg
• Renal transplant rejection
• Diabetes mellitus (the commonest cause in many series, with infection)
• Systemic vasculitis

Other causes include dehydration, amyloidosis, trauma, contrast media, and cocaine.

Papillae sloughing results in gross haematuria and flank pain (colic). It carries a risk of ureteral obstruction and infection.

Chronic papillary necrosis causes interstitial nephritis, renal scarring, and chronic kidney disease. Analgesic abuse increases the risk of urothelial carcinoma of the renal pelvis.

• Acute: fever, chills, flank pain (renal colic from passage of necrotic papilla), gross haematuria, pyuria, and sepsis, often with acute kidney injury; passage of tissue fragments in the urine.
• Chronic or subclinical: asymptomatic with progressive renal impairment, sterile pyuria, microscopic haematuria, polyuria, nocturia (impaired concentrating ability), distal renal tubular acidosis, and hypertension.
• Anaemia that is out of proportion to renal failure (analgesic nephropathy), and sterile pyuria.
• Associated stigmata: sickle cell disease, diabetes, analgesic use (headache, back pain), peptic ulcer disease, and gastrointestinal bleeding.
• Recurrent urinary infection, with septic shock in severe infection with obstruction.

• Urinalysis: haematuria, pyuria, proteinuria (mild), papillary fragments in urine (microscopy of strained urine), and culture.
• Blood tests: creatinine and eGFR, electrolytes (hyperkalaemic distal renal tubular acidosis), complete blood count, sickle cell testing and haemoglobin electrophoresis, HbA1c, and inflammatory markers.
• CT urography (the preferred study): papillary blunting, cavities in the papillae, "ring" or "golf club" shaped contrast filled spaces, filling defects in the pelvis (sloughed papillae), calcification of the papilla ("signet ring" sign), and a shrunken kidney with irregular contour in chronic disease.
• Non-contrast CT is useful for calcified papillae and the "ring" sign in analgesic nephropathy (diffuse papillary calcification is highly specific).
• Intravenous pyelogram (historical): contrast tracking into papillary fornices, "lobster claw", "ring shadow", "club" calyces.
• Ultrasound: echogenic papillae, hydronephrosis, and shrunken kidneys.
• Retrograde pyelography or ureteroscopy for ureteral obstruction by sloughed papillae, with exclusion of tumour (urine cytology, ureteroscopy with biopsy, in analgesic abusers).
• Kidney biopsy is rarely needed.

Treatment targets the cause, with prevention of complications.

• Treat the precipitant. Stop analgesics and non-steroidal anti-inflammatory drugs (counsel on avoiding all of them). Control diabetes (HbA1c below 7 percent). Treat urinary tract infection with culture guided antibiotics (14 days for complicated infections). Relieve obstruction, ensure hydration, and avoid contrast and nephrotoxic medicines.
• In sickle cell disease: hydration, avoidance of dehydration, treatment of infection, and referral to haematology.
• Acute episode: aggressive intravenous hydration, analgesia (paracetamol, short term opioids; avoid non-steroidal drugs), and intravenous antibiotics for infected cases (ceftriaxone 2 g daily, piperacillin tazobactam 4.5 g every 6 to 8 hours, or ciprofloxacin 400 mg every 12 hours; adjust to renal function).
• Obstruction by sloughed papilla: ureteric stent or percutaneous nephrostomy for infection or acute renal failure. Retrieve the papilla endoscopically (ureteroscopy with basket or laser fragmentation). Stones may form around the necrotic tissue.
• Haemorrhage: usually self-limited; transfusion for severe anaemia; embolisation or nephrectomy rarely.
• Bilateral obstruction with renal failure: emergency decompression and dialysis if needed.
• Chronic kidney disease: blood pressure control (target below 130/80), ACE inhibitor or angiotensin receptor blocker for proteinuria, avoidance of nephrotoxins, management of anaemia, and nephrology follow up. Give bicarbonate (sodium bicarbonate 0.5 to 1 mEq/kg per day) for acidosis. Dialysis or transplantation for end stage disease.
• Surveillance for urothelial cancer in analgesic nephropathy: urine cytology and imaging yearly, with urology review for haematuria.
• Prognosis: depends on the underlying cause and extent; recovery occurs after the removal of the cause if early.