25: Nephrolithiasis Flashcards
1
Q
Causes of hypercalciuria
A
- Bone resorption (overactive osteoclasts)
- Hyperparathyroidism
- Hyperthyroidism
- Cancer
- Renal tubular acidosis
- Corticosteroids (prednisone)
- Vitamin D excess
- Vitamin D25
- Vitamin D1,25
- Inflammatory conditions
- Sarcoidosis
- Lymphoma
- Idiopathic
- Gut (absorptive)
- Bone (↑ turnover)
- Kidney (renal leak)
2
Q
Calcium oxalate stones
A
- 70% of stones
- Normally:
- 10% of dietary oxalate absorbed in colon
- 90% bound by Ca and passed via stool
- Risk factors for CaOx stone formation
- Hypercalciuria
- Hyperuricosuria (“salt out” CaOx)
- Hypocitraturia (**citrate **inhibits calcium crystal formation)
- Hyperoxaluria
- Low urine volume
- Medical conditions
- Malabsoprtion (IBD, gastric bypass –> ↑oxalate uptake in colon)
- Obesity/gout
- Genetic dz (hyperoxalosis)
- Envelope appearance on UA/micro
3
Q
Calcium phosphate stones
A
- 10-15% of stones
- Coffin lid appearance on UA/micro
- Risk factors:
- Hypercalciuria
- Alkaline urine pH (>7) (CaP forms under basic conditions)
- Medullary sponge kidney (cystic kidney dz)
- CaP crystals in the form of:
- **Apatite **(bones/teeth)
- Brushite (Ca monohydrogen phosphate): large stone, requires surgical removal
4
Q
Uric acid stones
A
- 10-15% of stones
- 2nd most common mineral type
- Diamond shape on UA/micro
- Risk factors:
- Acidic urine
- Gout
- Hyperuricemia
- Metabolic syndrome
- Malignancies
5
Q
Struvite stones
A
- “Staghorn” stones
- MgNH4PO4 + CaCO3
- From urease-producing bacteria
- Proteus
- Haemophilus
- Klebsiella
- Ureaplasma urealyticum
-
Risk factors:
- Women
- Chronic urinary obstruction
- Neurologic dysfunction
6
Q
Cystine stones
A
- AutR defect in tubular transporters of dibasic AA’s
- Cystine
- Ornithine
- Arginine
- Lysine
- Cystine insoluble in acidic urine
- Hexagonal urine crystals (less commonly, Staghorns) on UA/micro
7
Q
Drug-induced stones
A
Indinavir, bactrim, allopurinol
8
Q
Stone inhibitors
A
Negatively charged molecules (ionic or macromolecular/protein-based) that inhibit crystal nucleation by adsorbing onto crystal surface and interfering with lattice formation.
9
Q
Nephrolithiasis presentation
A
- Acute, colicky flank pain radiating to groin
- Exam: CVA tenderness may be present
- Hematuria (90% of cases; absence does not rule out stones)
- Less often presentations:
- Silent ureteral obstruction
- Unexplained persistent UTI
- Painless hematuria
10
Q
kidneys-ureters-bladder (KUB) radiograph
A
- To detect obvious abnormalities of the urinary system, such as kidney stones
- Sensitivity 45-85%
- Use in treatment planning (stone localization, diameter)
- Preferred method of follow-up for radio-opaque stones (visible)
- Cannot detect small stones
11
Q
Renal ultrasound
A
- Can image both radiolucent and radiopaque stones
- Low radiation exposure (can use in pregnant patients, children)
- High specificity (82-100%)
- Quantifying size for small stones (<5mm) poor
12
Q
Helical non-contrast CT urogram
A
- Study of choice (sens: 95-98%, spec: 98-100%)
- Can visualize uric acid stones by gray-scale methods
- Help dx UT abnormalities predisoposing to stones
- R/o conditions which may masquerade as renal colic (abdominal pain commonly caused by kidney stones)
13
Q
Likelihood of passage of ureteral stones
A
- If <2mm, 8 days to pass. Intervention unnecessary.
- If 4-6mm, 22 days to pass. Need for intervention in 50% of cases.
- If >6mm, intervention necessary.
14
Q
Main causes of stone formation
A
- Hypercalciuria
- Hyperoxalauria
- Alkalitic urine pH
- Hyperuricosuria
- UTI
- Low urine citrate
15
Q
Management: First time stone
A
- Risk factor assessment:
- Occupation/environment
- Family Hx
- Diet: protein, purines, Na, fluid, Ca, oxalate
- Rx: triamterene, sulfonamides, carbonic anhydrase inhibitors
- Lab evaluation:
- Creatinine, HCO3, Ca, Phos, PTH
- Urine analysis, Cx
- Referral to stone clinic if:
- Children
- Solitary kidney
- Struvite stones
- Abn renal funct
- RTA
