Renal Cystic Diseases

Autosomal Dominant Polycystic Kidney Disease:

Pathophysiology:

  • PKD can be either recessive or dominant; ADPKD is most common
  • 1:10,00
  • Mutations in PKD1 gene (chr 16) accounts for 85%, PKD2 gene (chr 4) accounts for 15%
    • PKD1 encodes a protein (polycystin) responsible for cell-cell and cell-matrix interactions + mechanosensor (sensing fluid flow by associating w\ cilia)
    • PKD2 encodes a protein that is Ca channel that associates w\ cilia -> control intracellular Ca in response to flow
    • Defect -> abnormal proliferation and apoptosis of tubular epithelial cells -> cysts growth
  • 50% will develop ESRD by the age of 50-60
  • Recurrent episodes of pyelonephritis and nephrolithiasis -> renal failure
  • Progressive loss of renal function is due to mechanical compression, apoptosis of the health tissue, and reactive fibrosis

Renal cystic diseases 1

 

Clinical features:

  • Acute loin pain \ hematuria -> hemorrhage into a cyst, cyst infection, or stone formation
  • Loin or abdominal discomfort -> increasing size of the kidneys
  • HTN (from the age of 20 onwards) due to focal compression of intra-renal arteries by cysts -> activation of renin-angiotensin system
  • Intracerebral berry aneurysm (most don’t rupture)
    • 10% of pts have a subarachnoid hemorrhage -> sudden onset or unusual character “thunder-clap” headache -> prompt investigations
  • Heart valve abnormalities (esp mitral valve prolapse), cysts in other organs, diverticula, hernias
  • On PE: palpable kidneys w\ nodular surface

Renal cystic diseases 2

 

Diagnosis:

  • US (screening method of choice) (start after the age of 20) -> multiple cysts on the kidney
  • MRI can also detect cysts
  • Molecular diagnosis by screening mutations in PKD1 or PKD2 (rarely used) (indicated if no FHx)
  • If FHx of subarachnoid hemorrhage, or high risk occupation (pilot), or if going under high risk surgery -> screen for intracerebral aneurysm by contrast spiral CT or MR angio

 

Treatment:

  • No cure
  • Chronic renal pain resistant to common analgesics (pressure of cyst) -> surgical decompression or laparoscopic cyst decortication
  • Infection of cysts -> antibiotics (poor penetration across the cyst wall -> use lipophilic antibiotics active against gram neg bacteria: co-trimoxazole ‘TMP\SMX’ and fluoroquinolone ‘ciprofloxacin’)
  • Control HTN (ACEI are first line agents)
  • If renal calculi form (usually uric acid -> radiolucent) -> treat them normally by percutaneous stone removal or extracorporeal lithotripsy
  • Some evidence shows that vasopressin V2 receptor antagonist (tolvaptan) -> can slow cyst formation in some pts by preventing collection of fluid in cysts
  • If renal failure -> dialysis or transplant

 


Autosomal Recessive Polycystic Kidney Diseases: Infantile PKD:

Pathophysiology:

  • Cysts in renal collecting ducts + hepatic fibrosis
  • 1:20,000

 

Clinical features:

  • Liver involvement, portal HTN and cholangitis
  • Enlarged kidneys -> abdominal distension
  • HTN
  • Pulmonary insufficiency 2ndry to pulmonary hypoplasia + enlarged kidneys -> limit diaphragmatic movement (pulmn complications -> morbidity\mortality in neonates)
  • Potter syndrome: newborns w\ severe ARPKD: oligohydramnios -> hypoplasia of the lungs, limb abnormalities (club feet), characteristic abnormal face

 

Diagnosis:

  • Prenatal US screening
  • US: renal cysts in the absence of renal cysts in either parent, hepatomegaly, dilated bile duct

 

Treatment:

  • No cure
  • Manage resp in newborns

 


Medullary Sponge Kidney: 

Pathophysiology:

  • Cystic dilation of the collecting duct
  • Hematuria, UTIs, nephrolithiasis
  • Associated w\ hyperparathyroidism and parathyroid adenoma

Renal cystic diseases 9

 

Diagnosis:

  • IVP (IV pyelogram) -> contrast is seen to fill dilated cystic tubule “bouquet of flowers”
  • “Swiss cheese” appearance on histological cross section
  • US: echogenic medullary pyramids

 


Medullary Cystic Disease: Juvenile Nephrolithiasis:

Pathophysiology:

  • Develops early in childhood
  • Autosomal recessive -> mutations in genes NPHP1-4
  • Dominant histological finding: interstitial inflammation + tubular atrophy -> later development of medullary cysts

 

Clinical features:

  • Polyuria, polydipsia, and growth retardation

 

Diagnosis:

  • FHx and renal biopsy (cysts rarely visualized by imaging)

 


Simple Renal Cysts:

  • Very common (50% of the people over age 50)
  • Single\multiple
  • Asx, discovered incidentally
  • No treatment required in most

Renal cystic diseases 12

 


Download the PDF version: here


References:

  • The Johns Hopkins Internal Medicine Board Review
  • Davidson’s Principles and Practice of Medicine
  • Step up to medicine
  • Toronto notes

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