Urinary calculi | Urolithiasis

Urolithiasis (Urinary Tract Stones) is a urological term used to describe the process of forming stony concretions in the kidney, bladder, and urinary tract. Urinary calculus is a structure which forms and grows in the urinary tract when the urine is supersaturated with salt and minerals such as calcium oxalate, uric acid, cystine and struvite, which results in urinary obstruction due to impairment of the urinary flow along the urinary tract. Urinary calculi range by size from microscopic crystalline foci to calculi several centimeters in diameter.[1]

Etiology

Nearly 80% of calculi are made of calcium oxalate, it affects 5% of people with hyperparathyroidism. Moreover, it is also common in people who have systemic autoimmune diseases, such as sarcoidosis, etc.

Almost 5% of calculi are made of uric acid, this condition occur more often among patients with increased urine acidity.

Almost 2% of calculi are made of cystine cystinuria, it can be easily detected in the urine by a urinalysis test.

Nearly 3% of calculi are made of struvate (magnesium ammonium phosphate), which is common in people suffering of Recurrent urinary tract infections (UTIs), and especially in women suffering of Recurrent Urea-splitting UTIs.

Pathogenesis

Several risk factors are recognized to increase the potential of developing Urolithiasis, such as:

Super saturation of urine with calculus forming salts, variation in urine characteristics is a chronic procedure that builds overtime. However, three main contributing factors are:

1. Over excretion of salt (sodium and potassium), the excretion of salt is related to hypertension, which in turn is associated with abnormalities of calcium metabolism, leading to hyperparathyroidism, increased movement of calcium from bone and increased risk of urolithiasis due to increased renal excretion of calcium.[2][3][4]
2. Urine acidity, the formation of kidney stones is strongly influenced by urinary pH (alkaline pH or acidic urine pH).
3. Low urine volume

The presence of Uric acid crystals or other calculi in the kidneys.

Idiopathic hypercalciuria, is a common metabolic abnormality in patients with calcium calculi, it is characterized by calcium excretion that is above 300 mg/day.

Hypocitraturia is a medical term used to describe a common metabolic abnormality found in 20% to 60% of patients with urolithiasis, and especially in patients with recurrent calcium oxalate nephrolithiasis (recurrent calcium stone formers), it is characterized by citrate excretion of less than 320 mg per day. Normally, calcium and citrate combine to form Calcium citrate that is sparingly soluble in water (a soluble citrate complex).[5][6]

Hyperoxaluria is a medical term used to describe a common abnormal finding in patients with calcium oxalate nephrolithiasis (calcium oxalate kidney stones), it is characterized by excessive urinary excretion of oxalate that is above 40 mg/day. It can be caused by two conditions:

• Excess oxalate absorption in patients with diseases such as chronic pancreatitis, biliary disease, bacterial overgrowth syndrome, etc.
• Excess intake of food that contain massive amounts of oxalate such as spinach, cacao, nuts, pepper, tea, etc.

Hyperuricosuria is a medical term used to describe a common abnormal finding referring to increased renal excretion of uric acid, it is characterized by excessive urinary excretion of uric acid that is greater than 800 mg/day in men and greater than 750 mg/day in women. Crystals of uric acid provide nodes for calcium oxylate precipitation and increases the risk of calcium oxalate and calcium phosphate crystallization, these Calcium oxalate crystals become large enough to form calcium oxalate and Uric acid stones in the kidney. Uric acid stones may also be partially composed of calcium oxalate. Eating a diet that contain massive levels of purines (fish, meat or poultry) raises uric acid levels in the blood and can increase your risk of developing diseases like podagra or gout, which can lead to kidney stones.

Symptoms of urinary calculi

• Pain
• Patients with urinary calculi (Urolithiasis) often complain of impaired urinary elimination related to obstruction from renal calculi.
• Blood in urine (hematuria), most people with kidney stones will have blood in the urine.
• Renal colic is a type of severe and localized low back pain, often radiating to one side of the flank or lower abdomen, which usually occur when a stone is being passed along the urinary tract or when a stone (urolithiasis) gets stuck in the kidney, ureter, bladder or urethra.
• Crampy flank pain and migratory abdominal pain radiating across the abdomen along the course of the ureter to the external abdominal ring and may shoot into the groin, scrotum and the labia.

1^st step before the Diagnosis of urinary calculi

• Measure plasma Ca on 2 occasions to deny or confirm hyperparathyroidism.
• Monitor total urine output and patterns of voiding.
• Drinking more water, drink more than 2 liters per day, to flush out toxins.
• Intravenous pyelogram (IVP) of the patients to investigate anatomic abnormalities in lower calyx.
• Obtaining proper dietary history.
• Metabolic evaluation: increased calciuria, hypocitraturia, hyper uricosuria

2^nd step Diagnosis of urinary calculi

• Urine analysis, to deny or confirm micro or macro hematuria, pyuria (with or without apparent bacteriuria).
• X-ray to confirm or exclude the presence of urinary calculi, it identifies all stone types excluding uric acid calculi.
• Ultrasonography
• Retrograde urography (IVU or Retrograde pyelogram)
• Non contrast spiral Ct for patients with suspected renal colic.

Differential diagnosis

Differential diagnosis of urolithiasis is carried with appendicitis, cholecystitis,  peptic ulcer disease, ectopic pregnancy, pancreatitis or dissecting aneurysm.

Treatment

The management of urolithiasis will depend on the specific patient case, as well as it addresses the underlying causes of it.

Morphine 10-15 mg IM  q 3-5 hrs for moderate to severe pain.[1]

Shock wave lithotripsy (SWL) is the most common treatment for renal calculi measuring less than 2 cm in the united states; However, paracutaneous nephrolithotomy is indicated for the treatment of larger renal calculi (>2 cm).[22][23][24]

Hypercalciuria can usually be controlled by trichlormethiazide (2 mg/day), especially in severe and resistant cases; However, all patients with hypercalciuria require a strict carefully planned diet.[19][20][21]

Oral rehydration therapy (ORT) by increasing fluid intake to more than 3 liters per day.

Gradual replacement of potassium if serum potassium level drops below 3.5 mEq/L, a single dose of succinylcholine bid (0.5 mg for child, 1.0 mg for adolescent) will increase serum K+ by 0.5-1.0 mEq/L.[7][17][18]

Hypocitruria can usually be controlled by potassium citrate at a dosage of 25-50 mEq/L bid.[8][9][13]

Hyperoxaluria can usually be controlled by pyridoxine (vitamin B6) at a dose of 5-500 mg/day PO.[10][11][12]

Hyperuricosuria can usually be controlled by allopurinol at a dosage of 300 mg/day orally to increase urine pH, and potassium citrate at a dosage of 40-80 mEq/L; However, all patients with hyperuricosuria require a strict carefully planned diet of meat & fish.[14][15][16]

 

 

 

References

Verified by: Dr.Diab (July 27, 2017)

Citation: Dr.Diab. (July 27, 2017). Urinary calculi Etiology Pathogenesis Diagnosis and Treatment. Medcoi Journal of Medicine, 28(2). urn:medcoi:article3272.