Diagnosis of Polycystic Kidney Disease (PKD)

The diagnosis of polycystic kidney disease depends upon the clinical findings and the imaging results.

Clinical presentation of autosomal recessive PKD

In the autosomal recessive form of polycystic kidney disease (ARPKD), the symptoms are present at birth or may develop in early infancy or in childhood. Rarely, the presentation is delayed to adulthood.

ARPKD in fetal life

Ultrasound findings in a fetus with ARPKD include:

• Diffusely echogenic kidneys
• Bilateral enlargement
• Shape conservation
• Reduced amniotic fluid volume
• Empty urinary bladder in some cases
• Hypoplastic lungs

ARPKD at birth

Typical symptoms include respiratory difficulty at birth with a grossly enlarged abdomen.

Abdominal imaging reveals the presence of bilaterally enlarged, echogenic kidneys.

Additional diagnostic features include:

• Biliary duct atresia
• Congenital hepatic fibrosis signaled by enlargement of the liver and spleen or the presence of esophageal varices
• No evidence of PKD in either biological parent
• Family history of ARPKD in a sibling established by histologic or genetic diagnosis

ARPKD in infancy

In infants, the diagnosis is based on clinical features and imaging findings such as:

• Palpable masses in the flank on both sides
• History of chronic lung infections or other lung symptoms which have not been diagnosed
• History of low amniotic fluid volume
• History of spontaneous pneumothorax in the immediate neonatal period
• Presence of hypertension
• Biliary duct ectasia
• Congenital hepatic fibrosis

ARPKD in childhood and later

In children or young adults, clinical features and imaging results which are strongly suggestive of ARPKD include:

• Bilaterally echogenic kidneys, enlarged, normal or small in size (due to progressive fibrosis)
• Signs and symptoms of portal hypertension
• Hepatosplenomegaly
• Bleeding from esophageal varices

Genetic testing in ARPKD

Various methods of molecular genetic testing are available to detect mutations in the PKHD1 gene, such as:

• Sequence analysis
• Targeted mutation analysis
• Deletion/duplication analysis using various polymerase chain reaction (PCR) techniques or probe amplification methods
• Linkage analysis if the family is available and willing to be tested.

The place of molecular genetic testing is when clinical features are not diagnostic but suspicion exists as to the condition.

Pre-implantation genetic testing is used by certain couples who wish to rule out the presence of the mutation already identified in their genes, in their offspring.

Clinical presentation of autosomal dominant PKD

Autosomal dominant PKD (ADPKD) often presents with a positive family history for the disease, and enlargement of the kidneys and the liver. The diagnosis is based upon the ultrasound findings.

Ultrasound findings in ADPKD

With a 50% risk for ADPKD, the characteristic findings on ultrasound include:

• Three or more cysts in the age group of 15-39 years
• Two or more cysts per kidney in the age group 40-59 years
• Enlargement and diffuse echoes without cysts in a young child
• Renal cysts bilaterally
• Cysts in the liver or pancreas most commonly but also in the seminal vesicles or arachnoid membrane

Extrarenal manifestations

Extrarenal findings may be present, such as

• Brain aneurysms
• Aortic root dilatation
• Thoracic aortic dissection
• Mitral valve prolapse
• Abdominal wall hernias
• Hypertension

Molecular genetic testing

Molecular genetic testing in the form of sequence analysis, or duplication/deletion analysis, of the PK1 and PKD2 genes, is often required for a definitive diagnosis if:

• the imaging tests are not conclusive
• the family history is negative for ADPKD
• the clinical features are more mild or intense than usual
• atypical clinical features are present
• there is a suspicion of another condition causing renal cysts

Screening for ADPKD

Once the gene variant responsible for the disease in a family is identified, it may be used for presymptomatic genetic diagnosis in:

• Other family members with suspicious imaging results
• Younger relatives who need a conclusive diagnosis because imaging is not reliable for the diagnosis of ADPKD before 30 years

Ultrasound or other imaging techniques are used to exclude ADPKD before living kidney donation from a related donor at risk for the disease.

The pattern of disease severity within a family line may help predict how much it will affect other members with the condition. The severity may vary depending on the genetic variability, the type of mutant gene and environmental factors.

Imaging techniques in PKD

Abdominal ultrasound examination with a high-resolution probe capable of picking up 1-2 cm cysts is usually preferred as the first choice for diagnosis, because of its:

• Non-invasive nature
• Cost-effectiveness
• Easy availability
• Avoidance of ionizing radiation or contrast agents
• Detailed accurate visualization

Other imaging techniques used to diagnose PKD include

• Magnetic resonance imaging (MRI) when ultrasound results are not definitive
• Computerized tomography scanning
• Magnetic resonance cholangiopancreatography (MRCP), which delineates the biliary ducts more clearly and may obviate the need for liver biopsy

References

• http://www.ncbi.nlm.nih.gov/books/NBK1326/
• http://www.nhs.uk/Conditions/Autosomal-dominant-polycystic-kidney-disease/Pages/Diagnosis.aspx
• http://emedicine.medscape.com/article/244907-workup#showall