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Polycystic Kidney Disease (PKD)

BASICS

  • Definition: Group of monogenic disorders resulting in renal cyst development. Two main types:
  • Autosomal dominant PKD (ADPKD)
  • Autosomal recessive PKD (ARPKD)
  • ADPKD: Common genetic disorder; usually late-onset, causes end-stage kidney disease (ESKD) in adults.
  • ARPKD: Usually presents in infants.

EPIDEMIOLOGY

  • ADPKD: Prevalence as ESKD — 8.7/million (US), 7/million (Europe)
  • ARPKD: Seen in neonates and children
  • ADPKD: One of the most common hereditary kidney disorders

ETIOLOGY & PATHOPHYSIOLOGY

  • ADPKD:
  • Mutations: PKD1 (85%), PKD2 (15%) — encode polycystin 1 (PC1) and polycystin 2 (PC2)
  • Pathology: Disrupted polycystin → progressive fluid-filled cysts → kidney enlargement, architecture distortion
  • Inheritance: Autosomal dominant
  • ARPKD:
  • Mutation: PKHD1 (chromosome 6) encoding fibrocystin
  • Inheritance: Autosomal recessive

RISK FACTORS

  • Family history of PKD

GENERAL PREVENTION

  • Genetic counseling

ASSOCIATED CONDITIONS

  • ADPKD:
  • Cysts: Liver (58–94%), pancreas (5%), seminal vesicles (40%), arachnoid (8%)
  • Vascular: Intracerebral aneurysms (6–16%), aortic root dilation, dissection
  • Cardiac: Mitral valve prolapse (25%), LVH
  • GI: Diverticular disease
  • ARPKD:
  • Liver involvement: congenital hepatic fibrosis, portal hypertension

DIAGNOSIS

History

  • ADPKD: Family history (15% de novo), flank pain (60%), hematuria, UTI, hypertension (50% by 20–34 y, 100% with ESKD), renal failure
  • ARPKD: Neonatal death (30%), enlarged echogenic kidneys, oligohydramnios (prenatal), childhood/adolescence — hypertension, varices, hypersplenism

Physical Exam

  • Hypertension
  • Flank masses

Differential Diagnosis

  • Tuberous sclerosis, Von Hippel-Lindau, nephronophthisis, multicystic dysplastic kidney, simple cysts, medullary sponge kidney, acquired cystic disease, renal neoplasms

Diagnostic Tests & Interpretation

  • Labs: Electrolytes, BUN/Cr, urinalysis, urinary citrate
  • ADPKD:
  • Renal dysfunction, impaired concentration, hypocitraturia, elevated Cr, hematuria, mild proteinuria
  • Imaging:
    • US: Best screening; >2 cysts by age 30 is diagnostic in at-risk. Bilateral enlargement, hepatic cysts pathognomonic.
    • MRI/CT: Preferred for initial evaluation, detects more cysts; <5 cysts by MRI in <40 y excludes diagnosis. Total kidney volume by imaging predicts progression.
  • Genetic testing: Available for equivocal imaging or living donors (PKD1/PKD2)
  • ARPKD:
  • US: Enlarged, hyperechoic kidneys
  • CT: More sensitive if diagnosis uncertain
  • Molecular diagnosis is gold standard
  • Other: Anemia, thrombocytopenia, leukopenia (ARPKD), presence of hepatic fibrosis (ARPKD)

TREATMENT

General Measures

  • BP: Moderate sodium restriction, weight control, regular exercise, aggressive BP control (<110/75 if <50y, preserved eGFR)
  • Pain: Analgesics, minimize NSAIDs
  • Urolithiasis: Alkalinization, hydration, surgery as needed
  • UTI/cyst infections: Lipid-soluble antibiotics (TMP-SMX, fluoroquinolones)
  • Dialysis: For ESKD
  • Hematuria: Reduce physical activity

Medication

  • Targeted therapy: Tolvaptan (reduces cyst growth and eGFR decline in early ADPKD; monitor liver function)
  • BP control: ACE inhibitors/ARBs preferred
  • Statins: For hyperlipidemia

Surgery/Procedures

  • Indications: Uncontrolled HTN, severe pain, renal function decline, recurrent UTI, hematuria/hemorrhage
  • Procedures: Cyst unroofing, percutaneous aspiration/sclerotherapy (rare), renal transplant for ESKD

FOLLOW-UP & ONGOING CARE

  • Monitor BP and renal function (Cr, eGFR) at least twice yearly
  • Hydration, treat infections/stones aggressively, avoid nephrotoxins
  • Screen for intracranial aneurysms
  • Low-protein, low-salt diet; high water intake (>3 L/day); limit caffeine

PROGNOSIS

  • ADPKD progression: Renal failure in 2% by 40y, 23% by 50y, 48% by 73y
  • ADPKD accounts for 10–15% of dialysis patients
  • Variable progression — some (PKD2/atypical) may never reach ESRD

COMPLICATIONS

  • Cyst rupture, infection, hemorrhage
  • Renal failure, stones, cholangitis

ICD-10

  • Q61.3 Polycystic kidney, unspecified
  • Q61.2 Polycystic kidney, adult type
  • Q61.1 Polycystic kidney, infantile type

CLINICAL PEARLS

  • Most PKD patients eventually develop ESKD. Hydration and blood pressure control are key.
  • Early nephrology consultation is valuable for disease counseling and progression prevention.
  • No treatment proven to prevent ESKD; tolvaptan may slow progression in early ADPKD.
  • Family/genetic counseling is critical.