Autosomal Dominant Polycystic Kidney Disease in PACES

How it presents in PACES

In the the abdominal station station, the classic ADPKD case is a patient with bilateral flank masses and the background stigmata of chronic kidney disease. Your job is to recognise that the masses are kidneys, not spleen, then to read the surrounding clues — an arteriovenous fistula, a transplant scar, a uraemic complexion — and assemble a complete story rather than just calling out an isolated finding.

The commonest permutations examiners build are native polycystic kidneys plus a fistula (on or being prepared for haemodialysis), native kidneys plus a nephrectomy scar, or native kidneys carrying a functioning iliac-fossa allograft. If a transplant is present, present the case as end-stage renal failure secondary to ADPKD with a renal transplant — not simply as a kidney transplant. There is almost always a second organ to find: a polycystic liver, palpable as firm nodular hepatomegaly, sits just above the right kidney.

Signs to look for

Expose fully to the inguinal creases and examine bimanually. The discriminating checklist:

• Bilateral, ballotable, nodular flank masses — bimanually palpable, moving down on inspiration, one kidney usually more prominent than the other (asymmetry is expected).
• The kidney-versus-spleen discriminator: you can get above the mass, it is resonant to percussion, and there is no notch. The spleen is dull, has a notch, and you cannot get above it.
• Nodular, firm, non-tender hepatomegaly = polycystic liver. Separate it from the contiguous right kidney by percussing up from the right iliac fossa: resonant (kidney) becomes dull (liver).
• CKD/uraemic stigmata: conjunctival pallor, a sallow uraemic tinge, excoriations from itch, a uraemic flap or bruising, sometimes a parathyroidectomy neck scar.
• State the dialysis access and RRT status explicitly — an actively needled fistula with a thrill means on haemodialysis; an immature, quiet fistula means pre-dialysis; a peritoneal dialysis catheter or an iliac-fossa graft with a Rutherford-Morrison scar means a transplant.
• Offer to complete: blood pressure (hypertension in ~75%), urine dipstick for haematuria and proteinuria, auscultation for mitral valve prolapse / aortic regurgitation, fundoscopy, and a family history of subarachnoid haemorrhage.

Confirming the diagnosis & differential

First-line confirmation is a renal ultrasound, interpreted against the age-stratified Ravine criteria in an at-risk relative: under 30 years, at least two cysts (uni- or bilateral); 30–59 years, at least two cysts in each kidney; 60 years and over, at least four in each. Genetic testing is reserved for equivocal cases or for screening a young at-risk relative — classically a potential kidney donor with no cysts on imaging.

For bilateral ballotable kidneys, ADPKD leads by a wide margin, but keep a sieve ready: bilateral hydronephrosis from bladder outlet obstruction; infiltration by amyloid or sarcoid; acromegaly; bilateral angiomyolipomas of tuberous sclerosis (look for adenoma sebaceum, shagreen patch, ash-leaf macule, subungual fibroma); von Hippel–Lindau; and, rarely truly ballotable, early diabetic nephropathy. If only one kidney is palpable, think asymmetric ADPKD, contralateral nephrectomy, renal cell carcinoma, hydronephrosis, renal vein thrombosis, or compensatory hypertrophy of a solitary kidney.

The most examined trap is the liver: a knobbly hepatomegaly here is polycystic liver disease, not cirrhosis or metastases. Synthetic function is preserved — no jaundice, no ascites, no stigmata of chronic liver disease — and the symptoms come from mass effect, not liver failure.

The viva: what examiners ask

• Genetics: autosomal dominant with near-100% penetrance. PKD1 (chromosome 16, polycystin-1) accounts for ~85% and is more severe with earlier end-stage disease; PKD2 (chromosome 4, polycystin-2) is ~10–15% and milder. PKD1 lies adjacent to TSC2, so a contiguous-gene deletion can cause both ADPKD and tuberous sclerosis.
• Extra-renal features: hepatic cysts are the commonest (present in most patients); also pancreatic and other visceral cysts; berry (intracranial) aneurysms at the MCA/ICA risking subarachnoid haemorrhage; mitral valve prolapse, mitral and aortic regurgitation; colonic diverticular disease; abdominal-wall hernias; AAA; and polycythaemia from raised EPO.
• Aneurysm screening: MR or CT angiography of the brain is selective, not routine — indicated with a family history of SAH or known aneurysm, a high-risk occupation, or before major surgery; rescreen roughly five-yearly if normal.
• Causes of abdominal pain in ADPKD: infected cyst, haemorrhage into a cyst, cyst rupture, nephrolithiasis, urinary obstruction, plus associated diverticulitis, strangulated hernia, or ruptured AAA.
• Management: blood pressure control with an ACEi/ARB (target ~130/80); tolvaptan (a vasopressin V2 antagonist) to slow cyst growth and eGFR decline in rapidly progressive disease, monitoring LFTs; avoid NSAIDs and tetracyclines; treat cyst infection with tissue-penetrating antibiotics (fluoroquinolones, co-trimoxazole, vancomycin); standard CKD/ESRF care; and family screening with genetic counselling.
• Prognosis: by age 60, around half need renal replacement therapy, worse with male sex, PKD1 and early onset.

Common pitfalls / how to score

• Under-exposing and balloting lateral fat while missing the medial kidneys — expose to the inguinal creases.
• Calling a flank mass a spleen because you skipped percussion and the get-above-it test.
• Stopping at the kidneys and missing the polycystic liver or an iliac-fossa allograft — the second organ is where marks are won and lost.
• Treating absent MVP or AR as excluding ADPKD; these are associated and often absent.
• Reading the nodular liver as cirrhosis; anchor instead on preserved synthetic function and call it ADPLD.
• Naming the diagnosis but failing to state the RRT status and access — a complete presentation ties the kidneys, the fistula/graft, and the CKD stigmata into one coherent narrative.