344.3 🏥 內科專科考前版

344.3.1 Mechanistic Deep Dive

344.3.1.1 Crystallization Process

  • Supersaturation of crystallizing solutes
  • Nucleation
  • Growth
  • Aggregation
  • Heterogeneous (nidus): epithelial cells, casts
  • Risk: low fluid + ↑ solute + acid/alkaline pH

344.3.1.2 Calcium Stone Formation

  • Hypercalciuria from intestinal absorption (absorptive), bone resorption (resorptive), renal leak
  • ↑ Oxalate (dietary, primary hyperoxaluria, enteric)
  • ↓ Citrate (inhibitor of stone formation)
  • Acid urine

344.3.1.3 Struvite Pathophysiology

  • Urease cleaves urea → NH3 + CO2
  • ↑ NH4+ + alkaline urine
  • Mg + NH4 + PO4 precipitate
  • Self-perpetuating cycle

344.3.2 Recent Trials & Updates

344.3.2.1 SUSPEND (2015) — Tamsulosin

  • Large multi-center
  • No overall benefit
  • Some benefit in distal stones

344.3.2.2 Lumasiran (2020) — Primary Hyperoxaluria

  • siRNA against AGXT
  • ↓ Urinary oxalate
  • FDA approved

344.3.2.3 Nedosiran

  • For PH1 + 2
  • siRNA
  • Phase 3 trials

344.3.2.4 Tamsulosin Updates

  • Still used despite SUSPEND
  • More benefit subgroups (5-10 mm distal)

344.3.2.5 Ureteroscopy Advances

  • High-power holmium lasers
  • Thulium fiber laser emerging
  • Single-use ureteroscopes

344.3.3 High-Yield Specialist Points

344.3.3.1 Stone Composition Spectrometry

  • Infrared spectroscopy gold standard
  • X-ray crystallography
  • Provides specific composition

344.3.3.2 Hounsfield Units (HU) Stone Density on CT

  • < 600 HU: uric acid (radiolucent on KUB)
  • 600-1000: cystine
  • 1000-1500: struvite, calcium phosphate

  • 1500: calcium oxalate (densest)

  • Helps planning lithotripsy

344.3.3.3 Metabolic Evaluation Timing

  • ~ 6 weeks after acute episode
  • 24-hour urine on usual diet
  • Repeat 1-2x with modifications

344.3.3.4 Citrate as Stone Inhibitor

  • Binds calcium in urine
  • Reduces aggregation
  • ↑ pH
  • Hypocitraturia common

344.3.3.5 Distal RTA + Stones

  • Calcium phosphate stones
  • Hypocitraturia (acidosis)
  • Persistent alkaline urine
  • Treatment: NaHCO3 + K citrate

344.3.3.6 Primary Hyperparathyroidism + Stones

  • Hypercalcemia + hypercalciuria
  • Workup: PTH, vitamin D, urine Ca
  • Parathyroidectomy curative

344.3.3.7 Sarcoidosis + Stones

  • Hypercalcemia (1α-hydroxylase in granulomas)
  • Steroids
  • Limit vitamin D

344.3.3.8 Bariatric Surgery + Stones

  • Roux-en-Y: hyperoxaluria
  • Sleeve: less hyperoxaluria
  • Calcium supplementation
  • Aggressive hydration

344.3.3.9 Hyperaldosteronism + Stones

  • ↓ Citrate
  • Spironolactone

344.3.3.10 Renal Tubular Acidosis (Type 1) Workup in Stone Patients

  • Acidosis with alkaline urine pH > 5.5
  • Citrate < 320 mg/d (women) / < 400 mg/d (men)
  • Suggests dRTA

344.3.3.11 Pediatric Stones

  • Increasing incidence
  • Often metabolic (cystinuria, hyperoxaluria, distal RTA)
  • Genetic testing
  • Aggressive metabolic workup

344.3.3.12 Stone Surveillance

  • Imaging q 1-2 yr
  • Stone analysis when passed
  • 24-hour urine after intervention

344.3.3.13 Future Therapies

  • siRNA for primary hyperoxaluria
  • Microbiome modulation (oxalobacter formigenes)
  • Improved lithotripsy technology

344.3.4 Pearls

  • Non-contrast CT: gold standard
  • Calcium oxalate: most common (70-80%)
  • Calcium phosphate: alkaline urine, RTA Type 1
  • Uric acid: acid urine, alkalinize + allopurinol
  • Struvite: urease bacteria + surgical
  • Cystine: hydration + alkalinize + tiopronin
  • NSAIDs: first-line analgesia
  • Tamsulosin: 5-10 mm distal ureteral (mixed evidence)
  • Urosepsis = emergency
  • Lumasiran: primary hyperoxaluria type 1