Polycystic Kidney Disease in Children
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Direct answer
Polycystic kidney disease in children is an inherited cystic kidney disorder, presenting as autosomal recessive ARPKD in the newborn or as autosomal dominant ADPKD in later childhood or adulthood. The key distinction is timing and liver involvement: ARPKD produces large echogenic kidneys and congenital hepatic fibrosis from birth, while ADPKD usually stays silent until its cysts enlarge over years.
What you must remember
- ARPKD gene: PKHD1, encoding fibrocystin, causes bilateral large echogenic kidneys and a ductal plate malformation of the liver.
- ADPKD genes: PKD1 causes most cases and PKD2 the remainder, with cysts that grow over decades.
- Potter sequence: oligohydramnios from poor fetal urine output causes pulmonary hypoplasia, Potter facies and limb deformities, a major cause of early death.
- Hepatic lesion: congenital hepatic fibrosis causes portal hypertension and recurrent cholangitis, which can outlast the kidney problem.
- Ultrasound clue: ARPKD shows enlarged, echogenic kidneys with tiny cysts; ADPKD shows numerous larger cysts in both kidneys and liver.
- Blood pressure: hypertension is early and often severe in ARPKD, managed with ACE inhibitors and other agents.
- Associations: ADPKD links with intracranial aneurysm and mitral valve prolapse, which matter for counselling.
Comparing the two forms
A newborn born at 36 weeks has a flat face, short limbs and breathing difficulty within hours of birth. Ultrasound shows bilaterally enlarged, echogenic kidneys and very little amniotic fluid, pointing to a neonatal cystic disease.
| Feature | ARPKD | ADPKD |
|---|---|---|
| Inheritance | Autosomal recessive | Autosomal dominant |
| Gene | PKHD1 | PKD1 or PKD2 |
| Typical presentation | Neonatal distress, Potter features, early hypertension | Usually adult, with flank pain and hypertension |
| Kidneys on ultrasound | Large, echogenic, tiny cysts | Enlarged, numerous larger cysts |
| Liver | Congenital hepatic fibrosis | Liver cysts |
A neonatal presentation with large echogenic kidneys points strongly to ARPKD, whereas multiple cysts in an adult point to ADPKD. Family history and liver findings support the diagnosis, and genetic testing confirms it.
Renal function at birth ranges from near-normal to severely impaired, so kidney size, blood pressure and respiratory status guide early management. Ultrasound is the first investigation, and it images the kidneys and liver in the same session.
Where the exam sets its traps
Marks are lost by confusing the neonatal and adult forms and by ignoring the lungs and liver.
- Trap: labelling every childhood polycystic kidney as ADPKD. Correct: a neonatal presentation with large echogenic kidneys points to ARPKD, since ADPKD rarely causes symptoms in infancy.
- Trap: treating Potter sequence as a renal problem that dialysis can fix. Correct: pulmonary hypoplasia from oligohydramnios is the lethal problem, so respiratory support comes first.
- Trap: forgetting the liver in ARPKD. Correct: congenital hepatic fibrosis causes portal hypertension and cholangitis, so long-term care must include the liver as well as the kidney.
Frequently asked questions
What distinguishes ARPKD from ADPKD on ultrasound?
ARPKD shows enlarged, echogenic kidneys with numerous tiny cysts, often with associated congenital hepatic fibrosis. ADPKD shows enlarged kidneys with numerous larger cysts in both kidneys and liver.
Why do neonates with ARPKD develop Potter sequence?
Poor renal function reduces fetal urine output, causing oligohydramnios that restricts lung growth and deforms the face and limbs. Pulmonary hypoplasia is then the main cause of early death in these infants.
Why is ADPKD uncommon as a cause of paediatric kidney failure?
ADPKD cysts take years to enlarge and reduce function, so most patients are asymptomatic until adulthood. Children may show hypertension occasionally, but kidney failure usually develops later in life.
What is the main liver complication of ARPKD?
Congenital hepatic fibrosis with ductal plate malformation causes portal hypertension, variceal bleeding and recurrent cholangitis. These liver problems can outlast kidney function and can dominate long-term care.