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POLYCYSTIC KIDNEY DISEASE

Written by Lauren Lee

Last Reviewed: April 2019

Review Due: April 2020

 

DEFINITION

‘an inherited disorder that causes the development of fluid-filled cysts in the kidneys, resulting in progressive kidney enlargement and renal insufficiency’

 

AETIOLOGY

Autosomal Dominant Polycystic Kidney Disease (ADPKD)

Requires inheritance of one copy of the defective gene

PKD1 Gene (Chromosome 16)

PKD2 Gene (Chromosome 4)

 

Autosomal Recessive Polycystic Kidney Disease (ARPKD)

Requires inheritance of two copies of the mutated gene

PKHD1 Gene (Chromosome 6)

SIGNS AND SYMPTOMS

  • ADPKD

    • Flank Pain

    • Haematuria

    • Headaches

    • Blurred Vision

    • Urinary Tract Infections

    • Urolithiasis

 

It is important to note that although PKD1 and PKD2 (genes associated with ADPKD) overlap phenotypically, PKD1 is associated with more severe renal disease at an earlier age.

  • ARPKD

    • Enlarged Kidneys

    • Potter Sequence – Flattened Nose, Recessed Chin, Epicanthal Folds, Low-set Ears

    • Pulmonary Hypoplasia – Causing respiratory insufficiency in neonates

    • Congenital Hepatic Fibrosis – Causing portal hypertension

    • Dilated Intrahepatic Ducts – Causing cholestasis

 

PATHOPHYSIOLOGY

In ADPKD, PKD1 and PKD2 genes are responsible for the expression of polycystin proteins on primary cilia, necessary for inhibiting cell proliferation. Mutations in this gene cause abnormal cell proliferation and increased expression of cellular proteins that move water into the cyst.

 

Mutations in PKHD1 in ARPKD (coding for the fibrocystin protein) are also thought to cause cyst formation via a similar mechanism.

 

Investigations

Routine Bloods

FBC – Increased EPO secretion from cysts can raise hematocrit levels

U&Es – Calcium, Phosphorus

 

Urinalysis - Microalbuminuria (seen in 35% of ADPKD patients)

 

Midstream Specimen of Urine (MSSU) - For cytology and culture

 

Ultrasound

This is the major screening and diagnostic tool used in clinical practice because of its cost-effectiveness and safety

Renal cysts are common and increase in prevalence with age, meaning diagnostic criteria are age-dependent

Diagnostic Criteria:

≥ 2 renal cysts unilaterally/bilaterally (15-29 years old)

≥ 2 renal cysts in each kidney (30-59 years old)

≥ 4 renal cysts in each kidney (≥ 60 years old)

In ARPKD, unusually large or bright kidneys may be visualized on the scan

 

CT/MRI

These tools are not routinely used as CT exposes the patient to radiation and an MRI is much more expensive

They may be considered for use in younger individuals with indeterminate US results, as a method for exclusion of polycystic kidney disease

Screening for intracerebral aneurysms with MRI scanning may be indicated for patients at risk

 

Genetic Testing

This is not routinely performed as it can only identify ~70% of the different PKD1 and PKD2 mutations. However, it is commercially available for mutation screening

 

TREATMENT

Tolvaptan has recently been approved as a treatment for PKD. It can be used to slow down renal cyst growth and preserve kidney function. However, it is only indicated in adults that fit certain criteria:

  1. Patients with CKD Stage 2 or 3

  2. Patients with evidence of rapidly progressive kidney disease  

 

Outwith the use of Tolvaptan, treatment for ADPKD is directed at managing disease-related complications:

Hypertension – ACEi or ARBs

Infection – Antibiotics and supportive treatment

Nephrolithiasis – Painkillers and supportive treatment

Renal Failure – Renal Replacement Therapy

 

EPIDEMIOLOGY

The incidence of ADPKD in the UK is 1-2 per 1000, with a prevalence of 60,000 people. ARPKD is much less common, with an incidence of 5-10 per 100,000.

 

 
 

COMPLICATIONS

Renal Failure

Polycystic Kidney Disease is also associated with:

Cysts in other organs (e.g. liver and pancreas)

Aortic Root Dilatation (leading to aortic regurgitation)

Cerebral Aneurysms (which may rupture and cause a subarachnoid haemorrhage)

 

REFERENCES