ADPKD vs ARPKD: How to Tell Them Apart
Both ADPKD and ARPKD are inherited cystic kidney diseases that produce bilaterally enlarged kidneys and progress toward end-stage renal disease. The core axis that separates them is the pattern of inheritance and the age of onset: ADPKD is a dominant disease of adults with large visible cysts and liver cysts, while ARPKD is a recessive disease of infants with tiny collecting-duct cysts and obligatory congenital hepatic fibrosis.
How to tell them apart
| Feature | ADPKD (Autosomal Dominant Polycystic Kidney Disease) | ARPKD (Autosomal Recessive Polycystic Kidney Disease) |
|---|---|---|
| Inheritance | Autosomal DOMINANT — 50% risk to offspring | Autosomal RECESSIVE — 25% risk when both parents are carriers |
| Gene/Protein | PKD1 (85%, chromosome 16, more severe) or PKD2 (15%, chromosome 4, milder) / polycystin | PKHD1 / fibrocystin |
| Age of onset | Presents in the 30s–40s (cysts form earlier but symptoms come later) | Presents in infancy, often detected prenatally |
| Cyst appearance | Multiple large macrocysts of variable size, individually visible on imaging | Fusiform dilation of collecting ducts producing microcysts too small to visualize individually; kidneys appear echogenic |
| Liver involvement | Liver cysts (most common extrarenal manifestation); NO hepatic fibrosis | Congenital hepatic FIBROSIS is always present, leading to portal hypertension |
| Extrarenal manifestations | Intracranial (berry) aneurysms in 5–10%, mitral valve prolapse, colonic diverticula, hernias | Potter sequence if severe (oligohydramnios → pulmonary hypoplasia), portal hypertension |
| Prognosis | ESRD by age 50–60 in PKD1, or 70+ in PKD2 | 30% mortality in the first year of life (respiratory failure); survivors progress to ESRD |
| Treatment | Blood pressure control (target <130/80), tolvaptan to slow cyst growth and GFR decline, transplant for ESRD | Largely supportive — manage respiratory failure and portal hypertension |
The reasoning
Anchor first on age and inheritance. A neonate or infant — especially one with prenatal oligohydramnios, pulmonary hypoplasia, or a recessive family pattern — points to ARPKD, whereas a 30–40-year-old with a dominant (parent-affected) family history points to ADPKD. Confirm with imaging: discrete, individually visible macrocysts favor ADPKD, while diffusely echogenic kidneys without resolvable cysts favor ARPKD. Use the liver as the tie-breaker: benign hepatic cysts belong to ADPKD, but congenital hepatic fibrosis with portal hypertension is the obligatory hallmark of ARPKD. Genetic testing (PKD1/PKD2 vs PKHD1) settles ambiguous cases.
Key tests
- Renal ultrasound: ADPKD shows bilaterally enlarged kidneys with multiple discrete large cysts (Pei/Ravine age-based criteria in at-risk patients: ≥3 cysts unilateral or bilateral at ages 15–39, ≥2 cysts in each kidney at ages 40–59, and ≥4 cysts in each kidney at age ≥60); ARPKD shows enlarged, diffusely echogenic kidneys because the collecting-duct microcysts are too small to resolve individually.
- Genetic testing: identifies PKD1 or PKD2 (polycystin) mutations in ADPKD versus PKHD1 (fibrocystin) mutations in ARPKD when imaging is inconclusive.
- Liver imaging/evaluation: ADPKD demonstrates discrete hepatic cysts without fibrosis, whereas ARPKD demonstrates congenital hepatic fibrosis with signs of portal hypertension.
- MRA of cerebral vessels: relevant in ADPKD to screen for intracranial aneurysms (present in 5–10%) when there is a family history of aneurysm or SAH — a complication not associated with ARPKD.
What they share
- Bilaterally enlarged kidneys
- Progression to end-stage renal disease (ESRD)
- Cystic kidney pathology detectable on imaging
- Liver involvement (though of different types)
Pitfalls
- Assuming any polycystic kidney in a child is ADPKD — infantile presentation with echogenic kidneys and hepatic fibrosis is ARPKD, not early ADPKD.
- Confusing the two forms of liver disease: ADPKD causes hepatic cysts without fibrosis, while ARPKD causes congenital hepatic fibrosis leading to portal hypertension.
- Forgetting to screen for intracranial aneurysms in ADPKD (MRA when there is a family history of aneurysm or SAH); aneurysms are an ADPKD, not ARPKD, complication.
- Misreading ARPKD imaging as normal or non-cystic because the collecting-duct microcysts are too small to see individually and instead appear only as increased echogenicity.
- Misapplying the ultrasound diagnostic thresholds — the required cyst count for ADPKD rises with age (≥3 total at 15–39, ≥2 per kidney at 40–59, ≥4 per kidney at ≥60), so using a single fixed cutoff misclassifies patients.
Practice this the way the exam tests it — on branching cases where your decisions shape the patient.