Polycystic Kidney Disease

Meet the patient

A 30-year-old man walks into your clinic with a new blood pressure of 152 over 96. His father started dialysis at 55. On examination he has bilateral ballotable, irregularly lobulated renal masses and a midsystolic click. He has never seen a nephrologist, and the registrar wants to just treat the blood pressure. You do not — this is autosomal dominant polycystic kidney disease, and the next move is an ultrasound read against the Pei age-adjusted criteria.[1][3]

Two questions decide his decade, and they decide every ADPKD case: does he meet diagnostic criteria? (Pei answers it in minutes) and is he a rapid progressor? (Mayo imaging class answers it next). Hold those two and the whole page slots into place.[1]

One line to take seriously and never joke about: a thunderclap headache in ANY ADPKD patient is a subarachnoid haemorrhage from a ruptured berry aneurysm until proven otherwise. No CT, no discharge — whatever the hour.[9][10]

One gene, one cilium, two kidneys that never stop growing

ADPKD is a ciliopathy wearing a kidney costume. The primary (non-motile) cilium of every tubular cell carries a polycystin-1/2 complex that senses flow; lose it and the cell forgets it is a tubule and starts building a balloon. One defect, bilateral cysts from any nephron segment, and a characteristic set of extrarenal lesions — liver, berry aneurysm, mitral valve, pancreas, diverticula.[1]

It is the commonest monogenic kidney disease — prevalence 1 in 400 to 1 in 1000 live births, essentially 100 percent penetrant by modern imaging, and the fourth or fifth leading cause of ESKD worldwide, accounting for 5 to 10 percent of all dialysis patients. Severity varies widely, even within one family, because each cyst needs its own somatic second hit.[1]

Etymology for viva gold: cilium is Latin for eyelash — these hair-like flow sensors line every nephron, and polycystin is the protein their absence destroys. The old name adult polycystic misled a generation; gene testing shows cysts begin in childhood.[1]

The genetics — PKD1 and PKD2, and the severity ladder

In about 95 percent of families the disease is PKD1 or PKD2, and the gene predicts the decade of kidney failure.[1]

• PKD1 truncating — most families; chromosome 16p13.3; polycystin-1, a mechanosensory receptor; median ESKD about 55 years — the severe end.
• PKD1 non-truncating (in-frame) — median ESKD about 65 years.
• PKD2 — chromosome 4q22.1; polycystin-2, a TRP-family calcium channel; median ESKD about 74 years — milder, fewer and later cysts, less hypertension.
• Non-PKD ADPKD — monoallelic variants in ALG8, ALG9, GANAB, DNAJB11, IFT140 in about 2 percent; usually milder and atypical on imaging.
• Contiguous TSC2-PKD1 deletion — severe very-early-onset disease bundled with tuberous sclerosis features (ash-leaf macules, angiomyolipomas, seizures).[1]

About 5 to 10 percent of cases are de novo — a blank family tree does not exclude ADPKD. Next-generation sequencing with copy-number analysis finds a pathogenic variant in roughly 75 to 90 percent of typical cases.[1][10]

The ciliopathy cascade — why the cyst fills with fluid

The cyst is a tubular cell that lost its calcium brake. Polycystin-1 (a mechanosensory receptor) and polycystin-2 (a TRP calcium channel) sit as a complex in the primary cilium, plasma membrane and endoplasmic reticulum. Bending of the cilium by tubular flow normally drives a calcium influx that keeps intracellular calcium up and cAMP down. Lose the complex and the brake comes off.[1]

The two-hit model (Knudson) explains why cysts are focal. Inheritance is dominant, but each individual cyst needs a somatic second hit — mutation, loss of heterozygosity, or epigenetic silencing — on the remaining wild-type allele. One germline mutation, thousands of independent second hits, an asymmetric expanding cyst population.[1]

The downstream cascade is one coherent biochemical phenotype:[1]

• Low intracellular calcium (loss of the polycystin-2 channel).
• High cAMP — low calcium disinhibits adenylyl cyclase 6 and blunts PDE1, so cAMP climbs.
• Vasopressin V2-receptor signalling amplifies cAMP — and this is the exact target of tolvaptan.
• cAMP drives PKA then B-Raf and MAPK (ERK) — epithelial proliferation, the cyst lining multiplies.
• cAMP drives CFTR-mediated chloride and fluid secretion into the lumen — why cysts are fluid-filled, and why CFTR inhibitors slow them in vitro.
• mTOR activation fuels protein synthesis and proliferation; mTOR inhibitors worked in models but disappointed in patients.
• RAAS, inflammation and fibrosis — cysts compress neighbouring vessels, causing ischaemia, local renin release and interstitial fibrosis that ultimately destroys GFR.[1]

Once a cyst dilates past about 2 mm its tubular connection pinches off, so the cyst is now a closed sac enlarging by polarised fluid secretion alone — which is why an infected cyst can have a negative urine culture and why only lipophilic, cyst-penetrating antibiotics reach it.[1]

The 3-2-4 rule — Pei age-adjusted ultrasound

For an at-risk first-degree relative, three numbers make the diagnosis at the bedside: 3, 2, 4. Read the ultrasound against the patient's age.[3]

[3]

The classic trap: a 30-year-old relative with two cysts does not yet meet criteria (he needs three at that age) — but a single normal scan at 20 does not exclude ADPKD either, because cysts accrue with age. Repeat the scan, or test the known family mutation. CT and MRI are more sensitive and use a lower bar: at least 3 cysts age 15 to 40, at least 5 cysts in each kidney over age 40.[3][1]

Mayo 1A to 1E — who is the rapid progressor?

Total kidney volume predicts the year of kidney failure, and the Mayo class turns that volume into a treatment decision. Height-adjusted total kidney volume (htTKV) on MRI stratifies the typical expanding phenotype into five classes by annual growth rate.[8]

• 1A — under about 1.5 percent per year; ESKD unlikely before 70.
• 1B — about 1.5 to 3 percent per year; intermediate.
• 1C — about 3 to 4.5 percent per year.
• 1D — about 4.5 to 6 percent per year.
• 1E — over 6 percent per year; the most rapidly progressive.
• Mayo 1C through 1E defines rapidly progressive disease — and this is the trigger for tolvaptan. Class 2 (atypical, asymmetric or unilateral) does not get tolvaptan.[8]

What juniors write versus what gets marks. GFR stays normal for decades while the kidneys balloon, then cliffs — so a normal creatinine in a 30-year-old with huge kidneys means nothing about trajectory. The decision is driven by kidney volume and its growth rate, not by today's eGFR. An eGFR decline over 2.5 to 3 mL/min/1.73 sq m/yr, or Mayo 1C to 1E, is rapidly progressive disease.[8][9]

The kidney that declares itself in the 30s

Hypertension is usually the first sign, and it arrives years before the creatinine moves. ADPKD typically presents in the 3rd to 5th decade with high blood pressure, flank or abdominal pain, haematuria, or a UTI — and palpable bilateral irregular kidneys once the disease is established.[1][10]

[1]

The hypertension is driven by cyst compression of intrarenal arterioles (focal ischaemia, local renin release), sympathetic overactivity and endothelial dysfunction — and it begins before GFR falls, which is why tight blood-pressure control is a disease-modifying move, not just cardiovascular hygiene.[1]

The four flank pains — pick the right one

Flank pain is the commonest reason an ADPKD patient comes to the emergency department, and the four causes need four different investigations and four different treatments. Do not reach for the same analgesic pathway for all of them.[10]

[1] [1]

The classic trap: an infected cyst with a negative urine culture in a patient with flank pain and fever is the recurring miss — reach for a cyst-penetrating fluoroquinolone or clindamycin, not a beta-lactam or aminoglycoside, which do not enter cyst fluid.[1][10]

Macroscopic haematuria — classically after minor trauma, exercise, or in the anticoagulated patient — is usually a cyst rupture into the collecting system and settles with bed rest, hydration and analgesia over days. Persistent, painless, or constitutional haematuria must be imaged: never attribute it to just a cyst bleed and miss a coexisting renal cell carcinoma in a complex cyst.[1][10]

The extrarenal triad — liver, berry, valve

Three extrarenal lesions account for almost every non-renal mark in an ADPKD viva: polycystic liver disease, intracranial berry aneurysm, and mitral valve prolapse.[1]

[1] [1]

Berry aneurysms cluster in the anterior circulation — internal carotid and middle cerebral bifurcations — and are the most feared extrarenal complication because rupture is often lethal. Risk factors for rupture are aneurysm size (greatest above 7 mm), posterior-circulation location, uncontrolled hypertension, smoking, prior rupture, and a family history of aneurysm or SAH. The herald is the thunderclap worst-ever headache, with photophobia, neck stiffness or loss of consciousness. This is the one ADPKD scenario with no room for humour — see the thunderclap, scan the head.[9][10]

Not all bilateral cysts are ADPKD

Bilateral renal cysts are common; ADPKD is one specific cause with a family history, enlarged kidneys, and the extrarenal triad. Separate the mimics at the bedside before reaching for genetic testing.[1]

• Multiple simple cysts (Bosniak I) — few, smooth, thin-walled, anechoic, normal-sized kidneys, no family history; common in the elderly.
• Acquired cystic kidney disease — develops in dialysis-dependent ESKD with small shrunken kidneys (the opposite of ADPKD) and a higher RCC risk.
• Tuberous sclerosis complex — angiofibromas, ash-leaf macules, seizures, renal angiomyolipomas; the contiguous TSC2-PKD1 deletion causes severe early polycystic kidneys.
• von Hippel-Lindau disease — renal cell carcinoma, pancreatic cysts, haemangioblastoma, retinal angioma, phaeochromocytoma.
• Medullary sponge kidney — papillary collecting-duct ectasia with nephrocalcinosis, normal kidney size, no ESKD.
• Autosomal recessive PKD — neonatal huge echogenic kidneys, congenital hepatic fibrosis, PKHD1.
• Bilateral hydronephrosis — dilated pelvicalyceal system with thin parenchyma and an obstructive cause; no parenchymal cysts.[1]

Investigations — imaging first, then genetics

Ultrasound makes the diagnosis; Mayo class on MRI sets the prognosis; genetics closes the atypical case. A three-generation pedigree is part of the work-up, not an afterthought.[1]

• Imaging — ultrasound read against Pei for screening; MRI for htTKV and Mayo class; contrast CT only when a complex cyst or haemorrhage is suspected.
• Genetic testing — when the phenotype is atypical or mild, very early onset, no family history, for a potential living related donor, or for reproductive counselling. The panel covers PKD1, PKD2 (with copy-number analysis of the PKD1 duplicated region) and the non-PKD genes.
• Baseline bloods — urea and electrolytes, creatinine, eGFR (CKD-EPI 2021), urinalysis, urine ACR or PCR, full blood count and iron studies (ADPKD keeps haemoglobin better than other ESKD causes because erythropoietin is preserved), LFTs before tolvaptan, lipids, urate, glucose, HbA1c, bone biochemistry.
• Selective intracranial aneurysm screening — MRA (time-of-flight, no contrast), not routine. Screen only with a family history of aneurysm or SAH, prior rupture, uncontrolled hypertension, smoking, age over 50, a high-risk occupation, or before major elective surgery or transplant work-up.[1][9]

Everyone forgets: routine aneurysm screening of all ADPKD patients is not recommended — low yield, real false-positive risk. Reserve it for the groups above.[9][10]

Management — the four-step ladder

[1]

The ladder has four rungs: control the pressure, modify the disease, treat the complications, plan for ESKD. Salt and water are drugs in this condition, and tolvaptan is for the rapid progressor, not for everyone.[1][9]

Step 1 — Blood pressure, with an ACE inhibitor or ARB

Target under 110 over 80 in young adults with eGFR over 30, using an ACE inhibitor or an ARB — never both. HALT-PKD showed that rigorous control (95 to 110 over 60 to 75) with RAAS blockade slowed kidney growth without accelerating the GFR decline, and the same trial proved dietary salt restriction beneficial.[7][9]

• First line: ACE inhibitor or ARB — ramipril, lisinopril, enalapril, or telmisartan, losartan, valsartan. RAAS is central to ADPKD hypertension and progression.
• Second line: long-acting dihydropyridine calcium-channel blocker (amlodipine 5 to 10 mg OD), beta-blocker, or a loop diuretic only if volume overloaded.
• Lifestyle: salt restriction under 6 g NaCl per day (proven in HALT-PKD), weight loss, aerobic exercise, stop smoking, limit alcohol, moderate protein (about 0.8 g/kg/day).
• Avoid: combined ACEi plus ARB (no benefit, more harm), and NSAIDs (accelerate CKD and raise bleeding risk).[7][1]

Check urea and electrolytes within 1 to 2 weeks of starting or titrating RAAS blockade — hyperkalaemia and a creatinine rise are the reasons it gets stopped.[1]

Step 2 — Tolvaptan for the rapid progressor

Tolvaptan, a vasopressin V2-receptor antagonist, is the one disease-modifying drug in ADPKD — and it belongs to Mayo 1C to 1E, not to every patient. By suppressing cAMP in the collecting duct it slows cyst growth and eGFR decline, delaying ESKD by years.[4][5]

[1] [6]

NICE, the EMA and KDIGO 2025 all endorse tolvaptan for rapidly progressive ADPKD with preserved-to-moderately-impaired renal function, with mandatory monthly LFT monitoring for 18 months then 3-monthly.[6][9]

Step 3 — Treat the complications

• Pain — paracetamol first, short opioid courses sparingly, never NSAIDs; for chronic pain consider nerve block, cyst aspiration-sclerotherapy (ethanol or minocycline), laparoscopic fenestration, or renal denervation; nephrectomy only for refractory pain, recurrent infection or bleeding, or to make space for a graft.
• Nephrolithiasis — high fluid intake (urine output over 3 L/day), oral potassium citrate 10 to 20 mEq PO TDS, thiazide (hydrochlorothiazide 25 mg OD or chlorthalidone) for hypercalciuria, salt and purine restriction; ESWL or flexible ureteroscopy for obstructing stones.
• Cyst infection — ciprofloxacin, clindamycin or chloramphenicol (cyst-penetrating) for 2 to 6 weeks; drain an infected cyst over 3 to 5 cm. Not an aminoglycoside or beta-lactam alone.
• Cyst haemorrhage — bed rest, hydration, paracetamol or opioid, stop anticoagulants, tranexamic acid for refractory bleed, selective renal arterial embolisation if life-threatening.[1]

Step 4 — ESKD care and family screening

Preemptive living-donor transplant is the preferred renal replacement therapy; dialysis is the backup. Peritoneal dialysis is technically harder with very large kidneys. Every potential living related donor must be excluded for ADPKD by age-appropriate imaging AND genetics — an at-risk relative under 30 needs both, because ultrasound can miss early cysts.[9][2]

Known aneurysms are watched with serial MRA every 2 to 5 years and intervened on if over 7 mm, growing, symptomatic, or in a high-risk location — endovascular coiling preferred, surgical clipping otherwise — alongside strict blood-pressure control and smoking cessation.[9]

[2]

Primary prevention is not possible — the mutation is present from conception — but disease-modifying prevention (early BP control, salt restriction, hydration, tolvaptan in rapid progressors) delays ESKD by years. Routine caffeine avoidance is not supported by current evidence, though moderation is reasonable.[10]

Polycystic liver disease

Most patients are asymptomatic and need nothing. For symptomatic disease: cyst aspiration-sclerotherapy for a single dominant cyst, laparoscopic fenestration, hepatic resection, selective hepatic artery embolisation for multiple cysts with preserved parenchyma, a somatostatin analogue (lanreotide 90 to 120 mg SC monthly, or octreotide LAR 20 to 40 mg IM monthly) to reduce liver volume, and liver transplant for massive disease with cachexia or venous obstruction.[10]

The four trials that decide an ADPKD viva

Name TEMPO 3:4, REPRISE, HALT-PKD and KDIGO 2025 and you have answered most of the evidence half of any ADPKD question.[1]

[1] [9]

Pitfalls and preventable harm

[10]

Everyone forgets: a normal creatinine in a young adult with massively enlarged kidneys is not reassurance — volume is the trajectory marker, and the tolvaptan decision is made on Mayo class and eGFR slope, not on a single GFR. And a complex cyst (Bosniak III or IV) in an ADPKD kidney is cancer until proven otherwise — never sclerose it.[8][10]

Ward-round test — three stems, thirty seconds each

Stem 1 — thunderclap headache on the ward (answer)

A 38-year-old woman with known ADPKD, on ramipril, calls the nurse at 2 am with the worst headache of her life, coming on in seconds, with neck stiffness. What do you do in the next 30 minutes? Model: This is subarachnoid haemorrhage from a ruptured berry aneurysm until proven otherwise — no room for wait and see. Secure ABC, control the blood pressure with IV labetalol or nicardipine, and get an emergency non-contrast CT head now (sensitivity about 100 percent in the first 24 hours). If the CT is negative but suspicion persists, lumbar puncture for xanthochromia. Refer urgently to neurosurgery or interventional neuroradiology for endovascular coiling (preferred) or surgical clipping. Do not discharge, do not delay for an MRI, and do not attribute it to a tension headache.[9][10]

Stem 2 — the rapid progressor from the clinic (answer)

A 29-year-old man with PKD1-truncating ADPKD has kidneys growing at over 5 percent per year (Mayo class 1D) and his eGFR has fallen from 88 to 74 over the last year. Blood pressure is controlled on ramipril. What is the next disease-modifying step? Model: This is rapidly progressive ADPKD (Mayo 1C to 1E) — he meets the trigger for tolvaptan, a vasopressin V2-receptor antagonist. Confirm eGFR is appropriate (generally over 25 to 30), counsel on the aquaresis (polyuria 3 to 6 L per day, free access to water), ensure reliable contraception (teratogenic), take baseline LFTs, and start 45/15 mg split-dose, titrating monthly to 60/30 then 90/30 mg per day. Then the monitoring that defines safe prescribing: transaminases monthly for 18 months, then 3-monthly, and serum sodium. The payoff is about 2 to 3 years of ESKD delay.[4][5][6]

Stem 3 — fever and flank pain with a negative urine culture (answer)

A 45-year-old with ADPKD presents with fever, rigors and right flank pain that is worse when she sits upright. Urine culture is negative, blood cultures grow E. coli, CRP is 220. The team starts IV gentamicin. What is wrong with this plan? Model: This is an infected cyst, not pyelonephritis — the negative urine culture is the clue (the cyst has pinched off from the tubule). Gentamicin (an aminoglycoside) and beta-lactams alone penetrate cyst fluid poorly. Switch to a cyst-penetrating antibiotic: ciprofloxacin 500 mg PO BD (or 400 mg IV BD), clindamycin 600 mg IV TDS, or chloramphenicol, for 2 weeks minimum (4 to 6 weeks for deep infection). Image with CT or MRI (and FDG-PET if occult), and drain an infected cyst over 3 to 5 cm or one that fails to respond.[1][10]

The mantra

Screen the family, control the pressure, tolvaptan the rapid progressor, CT the thunderclap.[1][9]

References

1. [1]Bergmann C, Guay-Woodford LM, Harris PC, Horie S, Peters DJM, Torres VE. Polycystic kidney disease Nat Rev Dis Primers, 2018.PMID 30523303
2. [2]Gimpel C, Bergmann C, Bockenhauer D, et al. International consensus statement on the diagnosis and management of autosomal dominant polycystic kidney disease in children and young people Nat Rev Nephrol, 2019.PMID 31118499
3. [3]Pei Y, Obaji J, Dupuis A, et al. Unified criteria for ultrasonographic diagnosis of ADPKD J Am Soc Nephrol, 2009.PMID 18945943
4. [4]Torres VE, Chapman AB, Devuyst O, et al. Tolvaptan in patients with autosomal dominant polycystic kidney disease N Engl J Med, 2012.PMID 23121377
5. [5]Torres VE, Chapman AB, Devuyst O, et al. Tolvaptan in Later-Stage Autosomal Dominant Polycystic Kidney Disease N Engl J Med, 2017.PMID 29105594
6. [6]Müller RU, Messchendorp AL, Birn H, et al. An update on the use of tolvaptan for autosomal dominant polycystic kidney disease: consensus statement on behalf of the ERA Working Group on Inherited Kidney Disorders, the European Rare Kidney Disease Reference Network and Polycystic Kidney Disease International Nephrol Dial Transplant, 2022.PMID 35134221
7. [7]Torres VE, Abebe KZ, Schrier RW, et al. Dietary salt restriction is beneficial to the management of autosomal dominant polycystic kidney disease Kidney Int, 2017.PMID 27993381
8. [8]Bae KT, Shi T, Tao C, et al. Expanded Imaging Classification of Autosomal Dominant Polycystic Kidney Disease J Am Soc Nephrol, 2020.PMID 32487558
9. [9]Dahl NK, August P, Besse W, et al. KDOQI US Commentary on the KDIGO 2025 Clinical Practice Guideline for the Evaluation, Management, and Treatment of Autosomal Dominant Polycystic Kidney Disease (ADPKD) Am J Kidney Dis, 2026.PMID 41864657
10. [10]Gordon CE, Garimella PS, Perrone RD, et al. Autosomal Dominant Polycystic Kidney Disease: Core Curriculum 2025 Am J Kidney Dis, 2025.PMID 40844441