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Pathophysiology
Clinical meaning
In autosomal dominant polycystic kidney disease (ADPKD), dysfunctional polycystin proteins on renal tubular cell cilia cause decreased intracellular calcium, which activates adenylyl cyclase and increases cyclic AMP (cAMP). Elevated cAMP drives two pathological processes: cyst epithelial cell proliferation and chloride-driven fluid secretion into cyst lumens. Vasopressin (ADH) binding to V2 receptors on collecting duct cells amplifies this cAMP-mediated cystogenesis. Tolvaptan selectively blocks V2 receptors, reducing cAMP levels in cyst-lining cells and slowing both cyst growth and total kidney volume (TKV) expansion. The TEMPO 3:4 and REPRISE trials demonstrated tolvaptan reduces TKV growth rate and slows eGFR decline. However, hepatotoxicity is a significant risk requiring intensive liver function monitoring. The NP must carefully select candidates using Mayo Imaging Classification (Class 1C-1E predict rapid progression), assess ADPKD risk using PROPKD score (PKD1 truncating mutations, male sex, early hypertension, early urological events), and implement structured monitoring protocols.
Diagnostics & workup:
- MRI-measured total kidney volume (TKV) using Mayo Imaging Classification to predict progression rate
- Serial eGFR using CKD-EPI equation every 3-6 months to track rate of decline
- Liver function tests (ALT, AST, total bilirubin) monthly for first 18 months of tolvaptan, then every 3 months
- Serum sodium (risk of hypernatremia from aquaretic effect) and serum osmolality
- Urine osmolality and 24-hour urine volume to confirm tolvaptan pharmacodynamic effect
- Genetic testing for PKD1 vs PKD2 mutation type to refine prognosis (PROPKD score)
- Serum creatinine, BUN, and urinalysis at each visit; urine albumin-to-creatinine ratio for proteinuria monitoring
Risk factors:
- PKD1 truncating mutation (fastest progression to ESRD, typically by age 55)
- Mayo Imaging Classification 1C, 1D, or 1E (high predicted TKV growth rate)
- Male sex with early-onset hypertension before age 35
- Early urological events (hematuria, flank pain, UTI before age 35)
- Large total kidney volume adjusted for height (htTKV >600 mL/m at baseline)
- Family history of early ESRD from ADPKD (before age 58)
- High PROPKD score (≥7 predicts ESRD before age 60)
Management
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Prescribing & monitoring
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Takeaways
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