Nephrolithiasis and LUTS Etiology

• Renal stones include nephrolithiasis (kidney stones), ureterolithiasis (ureter stones), and cystolithiasis (urinary bladder stones).

Renal Stone Types

• Calcium oxalate is the most common type of kidney stone.
• Calcium phosphate is the second most common type, often associated with RTA type 1 and alkaline urine.
• Struvite stones are associated with UTIs and urease-producing bacteria, leading to staghorn calculi and alkaline urine.
• Uric acid stones are linked to hyperuricemia, gout, tumor lysis syndrome, and acidic urine.
• Cysteine stones result from an autosomal recessive mutation affecting cysteine absorption, with acidic urine.
• Calcium oxalate and phosphate stones appear radiopaque on X-rays, while uric acid and cysteine stones are radiolucent.

Etiology

• Kidney stones form due to increased soluble materials, leading to urine supersaturation, crystallization, and nidus formation, primarily in renal tubules.
• Stone formation is prevented by inhibitors like citrate, magnesium, and pyrophosphate.
• Vitamin A deficiency and UTIs can contribute to stone formation.

Risk Factors

• Risk factors include being male, white, aged 20-40, and dehydration.
• Hot weather, outdoor work, previous kidney stone history, and diet high in salt, protein, and oxalate increase risk.
• Medical conditions like hypocitraturia, hypomagnesemia, hyperparathyroidism, gout, RTA type 1, and UTIs increase risk.
• Medications like acetazolamide, sulfadiazine, and loop diuretics increase kidney stone risk.

Clinical Features

• Kidney stones can be asymptomatic, especially if bilateral, or symptomatic.
• Pain occurs in 75% of symptomatic cases, presenting as renal pain from capsule distention or ureteric colic from obstruction.
• Renal or upper ureter stones cause flank pain that radiates anteriorly and inferiorly.
• Lower ureter stones cause iliac fossa pain radiating to the thigh and groin.
• Additional symptoms include hematuria, dysuria, frequency, and urgency, sometimes with fever if there is a UTI.

Physical Exam Findings

• Costovertebral angle (CVA) tenderness indicates pyelonephritis.
• Loin swelling indicates hydronephrosis, and genital or digital rectal exams (DRE) help rule out testicular torsion.

Sites of Stone Impaction

• Common sites of stone impaction include the calyx, ureteropelvic junction, near the pelvic brim, and the ureterovesical junction.

Investigations

• Labs include CBC to check for elevated WBCs indicating UTI or pyelonephritis.
• Urine analysis reveals hematuria, abnormal pH, crystals, and pyuria with nitrates if a UTI is present.
• Kidney function is assessed via a creatinine test to detect acute kidney injury.

Imaging

• A non-contrast CT scan is the gold standard for detecting all types of stones and ruling out other conditions.
• Ultrasound is used for pregnant females to show stones and hydronephrosis.
• X-rays are rarely used, as they do not show all stones.

Management

• Conservative treatment includes hydration and NSAIDs for pain relief for all patients with stones smaller than 5 mm.
• Extracorporeal shock wave lithotripsy (ESWL) is used for stones smaller than 2 cm, but it is contraindicated in pregnancy, current UTI, and coagulopathies.
• Percutaneous nephrolithotomy is performed for stones larger than 2 cm.
• Pyelolithotomy removes stones in the renal pelvis while ureteroscopic lithotomy uses ureteroscopy to remove stones in the ureter.
• Open surgery is reserved for large struvite stones or failed previous treatments.
• A double J stent can bypass the obstruction and relieve pain, indicated for multiple stones, bilateral obstruction, single kidney, or pregnancy.

Complications

• Complications include hydronephrosis, superimposed infections, acute renal failure, and pyelonephritis.

Differential Diagnosis

• The differential diagnosis depends on the upper or lower ureter location, including gynecological, prostate, or scrotum pathologies, diverticulitis, appendicitis, and cholecystitis.

Struvite Stones

• Struvite stones are staghorn calculi made of magnesium, ammonium, and phosphate, associated with UTIs caused by urease-positive bacteria like Proteus mirabilis.

Medical Treatment

• Thiazide diuretics and urine acidification are used for calcium phosphate stones.
• Thiazide diuretics and potassium citrate for urine alkalinization are treatments for Ca oxalate and uric acid stones.
• Penicillamine and urine alkalinization (potassium citrate) are used for cysteine stones, while struvite stones often require surgical removal.

Bladder Stones

• Bladder stones (cystolithiasis) cause pain, lower urinary tract symptoms (LUTS), and pain at the end of micturition which may refer to the tip of the penis or labia majora.
• Treatment includes conservative measures or transurethral cystolitholapaxy and can be secondary to BPH, foreign bodies, or neurogenic bladder.

Urethral Stones

• Urethral stones (urethrolithiasis) are more common in males and can be primary due to stricture or meatal stenosis, or secondary from bladder stones.

Notes

• Lower urinary stones are mostly secondary, and the hardest type of stone is calcium monohydrate.
• Proteus mirabilis is the most common microorganism causing renal stones.
• In bilateral renal stones, treat the kidney with better function first
• Chron's disease/pancreatic insufficiency may cause fat loss that binds with Ca+2, which in turn causes more circulating free phosphate that creates more kidney stones
• Short bowel syndrome causes hyperoxaluria and calcium oxalate stones.
• Dietary sources with high levels of oxalate include tomatoes and grapefruit.

Explore nephrolithiasis, its diagnosis via renal stone location, and the initial steps in urinary stone formation (LUTS). Understand the roles of urine supersaturation, nidus formation, and increased soluble material concentration. Identify risk factors like outdoor work and personal traits.