My Medical Note On Nephrolithiasis And Kidney Stones For The USMLE

Nephrolithiasis 
- Stones within the urinary tract
- Sites (CUUP)

i. UreteroVesicular junction (Where Ureter meets the bladder)
- Most common site

ii. Calyx
- Cup like extensions within the kidneys
- Cavity where urine collects before it flows through the pelvis, Ureter and into the bladder

iii. UreteroPelvic junction (UPJ)
- When the Pelvis meets the Ureter
- The Pelvis is wider than the ureter and drains the Kidneys into the ureter

iv. Intersection of Ureter and Iliac vessels (Near Pelvic brim)
 
*Pyridoxine deficiency may lead to hyperoxalaturia

Risk Factors of Nephrolithiasis (DULL HIM)

- Low fluid intake (Most common)
- Fam History
- Illnesses causing stones
- Loop diuretics and other medications
- Male gender (3x Female)
- UTIs (Urease-producing bacteria)
- Dietary (Low ca2+ and High Oxalate intake)

Mneimonic: DULL HIM

Illnesses causing kidney Stones

i. Gout
- Causes Uric acid stones
- Due to hyperuriceamia

ii. Crohn's disease
- Ileal dysfnx = Oxalate hyperabsorption
- Diarrhea also promotes the formation of Calcium-fatty acids salts = less ca2+ to bind oxalate in the intestinal lumen
- hypocitraturia and hypomagnesuria (they form soluble complex with calcium in the urine, increaes act of macromolecules eg Tamm-Horsfall protein, that inhibit ca oxalate aggregatn. citrate also helps bone formation)

iii. Hyperparathyroidism

iv. Type 1 RTA (Distal) - Renal Tubular Acidosis


Medications causing Kidney stones
i. Loop diuretics
ii. Acetazolamide
iii. Antacids
iv. Chemotherapy

 
Types of Kidney stones (SUCK)
1. Kalcium stones (Calcium)
2. Uric Acids
3. Struvite stones (AMP)
4. Cystine

Calcium Kidney stones
- most common (85%)
- Calcium Oxalate > Calcium Phosphate
- Bipyramidal (Envelope shaped) or Biconcave ovals
- Radiodense (Seen on Radiograph)
- Secondary to  
i. Hypercalciuria
ii. Hyperoxaluria
iii. Hypocitraturia
- Treat with
i. Thiazide diuretics
ii. Citrate
iii. Low-Sodium diet

Causes of Hypercalciuria
- Inc Intestinal absorption of Calcium
- Dec Renal calcium absorption
- Inc Renal excretion of calcium
- Inc Bone resorption
- Primary Hyperparathyroidism
- Sarcoidosis
- Malignancy
- Vitamin D excess

Causes of HyperOxaluria (Mostly Malabsorption)
- Severe Steatorrhea
- Small bowel disease
- Pyridoxine def (Vit B6 def)


Uric Acid Kidney stones
- Second most common
- Caused by persistently Acidic urine (<5.5)
- They form Flat square plates crystals
- These crystals escape x-rays detection
- Associated with
i. Hyperuriceamia
ii. Gout
iii. Chemotherapy (Leukemia/Lymphomas)
- Diagnosis
i. Flat square plates
ii. Radiolucent images (CT scan, Ultra Sound, IntraVenous Pyelogram)
- Treatment
i. Alkalinization of urine
ii. Allopurinol

- URIC Acid stones
U = US can dx
R = Romboid (Flat square plates)/Rosettes shape
I = IVP can dx
C = CT scan can dx

- Acid = Acidic urine promotes URIC acid stones


Struvite Kidney  stones (Ammonium Magnesium Phosphate stones)
- Also called Staghorn stones
- Radiodense crystals are formed (Rectangular Prisms)
- Common in pts with recurrent UTIs (due to urease +ve bacteria)
- Precipitates in Alkaline urine (Urea splitting bacteria convert urea to ammonia - Alkaline)
- Ammonia combines with Magnesium or Phosphate = Struvite stones
- may involve entire renal collecting system

Urea Splitting bacteria causing UTI (SPEK)

A SPEK in the UT = Staghorn/Struvite stone
Serratia
Proteus
Enterobacter
Klebsiella

- A SPEK in the UT is StruvitAL

Cystine stones
- least common (1%)
- Genetic predisposition = Cystinuria (Autosomal Recessive)
- Hexagon-shaped crystals (Sixtine - Six sizes)
- Can also staghorn
- Sodium Cyanide Nitroprusside test +VE
- Urine is acidic
- poorly visualized
- Cystine is poorly soluble
- PCT Cystine reabsorbing transporter losses fnx
- PCT defect causes poor reabsorption of  COLA
i. Cystine
ii. Ornithine
iii. Lysine
iv. Arginine

- Treat with Low sodium, Chelating agents, Alkalinization of urine


Course of Kidney stones (StONE)
- Patient may pass out stone < half of a 1cm
- Stone > 1cm gets stuck
- Recurrence is common (within 10 yrs)

Features
Classic Presentation of Nephrolithiasis
- Sudden onset of Colicky flank pain radiating to groin
- Urinalysis = Hematuria
- Renal colic (due ureteral obstruction and spasm (Sudden, becomes severe, cant sit still, occus in waves or paroxysms, begins in flank and radiates anteriorly)
- Nausea/Vomiting (Due to severe pain)
- Hematuria (>90% of cases)
- UTIs


Diagnosing Nephrolithiasis
1. Laboratory
2. Imaging

Laboratory diagnosis of Nephrolithiasis
i. Urinalysis
- If kidney is associated pain + Hematuria + Pyuria = Stone with Concomitant infection
- Microscopic or Gross hematuria
- Assoc UTI (Pyuria/Bacteriuria - SPEK)
- Examine Sediment for Crystals
* Envelope/ Dumbbell/ Wedge shape = Calcium
* Romboid/Rosettes shape = Uric acid
* Cysine - Hexagonal shape = Cystine
* Coffin lid shape = Struvite
- pH
* Decreased PH (Acidic Urine) = Cystine or Uric acid stone
* Increased pH (Basic Urine) = Calcium phospahte or Struvite

Culture
- If suspect infectn

24-hour urine
- Renal fnx (Cr)
- Ca, Urate, Oxalate, Citrate levels

Serum xmistry
- Renal fnx (BUN and Cr)
- Ca, Urate, Oxalate, Citrate levels

Associated pain + Hematuria + Pyuria = Stone with Concomitant infection


Imaging
Plain Radiograph (KUB,ie of the Kidney, Ureter and Bladder)
- initial imaging
- Acidic Urine - Cystine and Uric stones not seen on plain imaging

Spiral CT without contrast
- Gold standard for all stones

IntraVenous Pyelogram (IVP)
- defines degree and extent of obstruction
- helps in deciding need for procedural therapy
- Not needed for dx of stones

Renal US (UltraSound)
- detects hydronephrosis or hydroureter
- false -ve in early
- low visual yield
- choice for pts who can’t receive radiation (Pregnancy)


Stone (Attempt to recover stone passed)
- Helpful in achieving
i. Analysis of the stone and determination of the cause
ii. Choice of treatment
iii. Prevention
iv. Reporting history


Treatment of Nephrolithiasis 
1. General
2. Specific (Pain and Obstruction)
3. Preventive

General measures
- Tries to help the patient pass the stone with less pain, also treats underlying.
i. Analgesia
- IV Morphine, Parenteral NSAIDS (Ketorolac)
ii. Vigorous fluid hydration
iii. Antibiotics if UTI
iv. Consider Indications for admission

Indications for Hospitalization.
1. Pain refractory to Oral medications
2. Anuria (Most likey in a patient with a Single kidney)
3. Colic + UTI
4. Large stONE (>1cm)

Specific measures
- Based on Pain Severity

1. Mild-Moderate severity
- High Fluid intake
- Oral analgesia
- wait for stone to pass (Urine strainer)

2. Severe pain
- IV fluids
- KUB/IVP to find site
- If stone doesnt pass after 3 days = Urologist consult

Severe pain measure
- IV fluids + Narcotics
- KUB and IVP
- Urology consult if > 3days

If Obstruction + Persistent pain (refractory to Narcotics)
-  Surgery (Breaks the calculus for spontaneous passage)
- Extracorporeal shock wave lithotripsy (Most common, > 5mm, < 2cm stones) - ESWL
- Percutaneous nephrolithotomy (If Lithotripsy fails, best for >2cm stones) - PCNL

Shock Wave Lithotripsy (SWL) is the most common treatment for kidney stones in the U.S. Shock wavesfrom outside the body are targeted at a kidney stone causing the stone to fragment. The stones are broken into tiny pieces.

Percutaneous nephrolithotomy is a minimally-invasive procedure to remove stones from the kidney by a small puncture wound through the skin. It is most suitable to remove stones of more than 2 cm in size and which are present near the pelvic region. It is usually done under general anesthesia or spinal anesthesia.

Prevention of Kidney stones 
i. Dietary
ii. Pharmaceuticals

i. Dietary measures
- High fluid inake
- Limit animal protein (esp in hyperuricosuria)
- Limit calcium intake (esp in calcium stone

ii. Pharm measures to prevent Stones
* Thiazide diuretics
- Reduce urinary calcium (esp in Hypercalciuria)
- Allopurinol (Prevents recurrent uric acid stones)