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Urinary stones

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Urinary stone disease is a very common health issue. This disease has significant social impact also as it may cause significant pain and morbidity which would require abstinence from work and loss of productive hours. Urinary stone disease, also known as urolithiasis implies formation of solid stones in the urinary tract. The location of stones vary from kidney, ureter, urinary bladder and urethra. The usual place of origin of stones are either kidneys or urinary bladder.

The most common symptom caused by urinary stones is pain. The location of pain would vary depending on the location of the stone. A stone that obstructs the ureter or renal pelvis causes excruciating, intermittent pain that radiates from the flank to the groin or to the inner thigh. This pain, known as renal colic, is often described as one of the strongest pain sensations known. Renal colic caused by kidney stones is commonly accompanied by urinary urgency, restlessness, hematuria (blood in urine), sweating, nausea, and vomiting. It is typically described as colicky pain as it occurs in intervals in a crescendo pattern lasting 20 to 60 minutes caused by peristaltic contractions of the ureter as it attempts to expel the stone.

The embryological link between the urinary tract, the genital system, and the gastrointestinal tract isthe basis of the radiation of pain to the gonads, as well as the nausea and vomiting that are also common in urolithiasis. Fever that accompanies pain due to urinary stones may be an ominous sign that points towards infection. This would mandate prompt treatment for relieving obstructiondue to stone and also aggressive treatment of infection.

The above mentioned symptoms point towards a diagnosis of urinary stones. This needs to be confirmed with imaging studies to confirm the diagnosis of stone disease. The common tests performed are Urine analysis, Ultrasound scan (USS) and X ray of the abdomen. CT scan is
also increasingly being used to diagnose stone disease and would be the best test to correctly
iagnose and locate urinary stones. Additional information like clues to the hardness of stones
can also be ascertained with CT scan.

Stone disease may be seen from infancy to old age. However occurrence of stones in children mandates detailed evaluation to rule out any metabolic diseases that would predispose to stone disease. Men have 3-4 times greater chance of development of urinary stones. Stones that form in the urinary tract can be of varying chemical composition. Urinary stones form in concentrated urine when crystals formed from calcium, oxalate, phosphate, cystine, uric acid etc precipitate in urine. These crystals accumulate to form stones which grow in size with further accumulation of crystals. Epitaxy is the term used to denote overgrowth of one type of crystal on the surface of a preexisting one that is of different type. This kind of nucleation with different crystals are seen with calcium phosphate and uric acid facilitating the crystallization of

calcium oxalate salt. There are various organic (eg - glycosaminoglycans, nephrocalcin, Tamm- Horsfall protein, uropontin) and inorganic (eg - citrate, pyrophosphate) substances in urine that are inhibitors of stone formation. Any situation that changes the balance of these substances in urine can lead to stone formation. Crystal retention can occur due to the interaction of renal epithelial cells and salt crystal, which results in their internalization and submucosal plaque formation (Randall's plaque). These crystals aggregate and erode towards the luminal surface to form a nidus for further stone growth.

Peculiarities of diet, certain diseases and use of some drugs may predispose to stone formation. Stones differ in their chemical composition and so the reason for stone formation would also differ in different individuals.

Dietary factors
Low intake of fluids, dehydration
Low intake of calcium containing food - this can cause higher absorption of oxalate in the
diet which can cause urolithiasis.
Use of calcium supplements
High intake of non vegetarian food
High intake of sweets
High intake of sodium
High intake of leafy vegetables, chocolate, nuts.
Vitamin B6 deficiency
Diseases predisposing to stone formation
Hyperparathyroidism
Gout
Diabetes mellitus
Obesity
Crohn's disease
Gastro-intestinal bypass surgeries
Genetic diseases - Primary hyperoxaluria, Cystinuria, Lesch-Nyhan syndrome, Familial renal
tubular acidosis

The decision to treat urinary stones depend on various factors like location and size of stones, presence of obstruction to urinary tract, co existing alteration in kidney function, co existing urinary infection etc. Small stones in the kidneys are usually treated with medicines. When these stones are expelled, there is a chance of occurrence of pain. This is usually treated with painkillers, but further treatment would be ultimately determined by the patient's ability to tolerate pain and constraints and circumstances of the patient. Stones which are refractory to medical treatment and stones which are larger in size are treated with procedures that aim at clearance of stones. If there is associated infection, this is tackled first and any procedure to clear stones is done only after infection is treated adequately. When there is concurrent infection, a procedure called stenting is done to allow relief of obstruction by stone and to clear infected urine. The actual procedure to clear stone is done after several days of stenting.

Treatment decisions regarding kidney stones are taken taking into consideration the location and size of stone, density of stone, anatomy of urinary tract inside the kidney etc. All treatment modalities may not suit to clear a given stone. The following are the usual procedures adopted
to clear urinary stones - ESWL (Extra-corporeal Shock Wave Lithotripsy) - This modality uses shock waves to fragment stones inside the kidney or upper ureter. The stone which is broken down into fragments is then passed through urine. It is difficult to treat large stones and hard stones with this modality. There is also a chance of stone fragments getting stuck in the ureter causing pain. PCNL (Per Cutaneous Nephro Lithotripsy) - This is a minimally invasive surgery involving introduction of in instrument directly into the kidney to clear stones. This is a kind of 'key hole' surgery for kidney stones.

Ureteroscopy - This procedure involves introduction of instruments through the urethra into the bladder and then into the ureter to visualize the stone and fragment the stones. Ureteric stones are best treated by this method. Flexible ureteroscopy is a modification of this procedure by
which the instrument called flexible urerteroscope is introduced into the ureter or kidney to tackle stones. Stones are fragmented using either laser energy or a pneumatic lithotriptor, which uses mechanical energy to fragment stones. Flexible ureteroscopy to clear kidney stones is also
called as RIRS (Retrograde Intra Renal Surgery). Cystolitholapaxy - This is the process of breaking bladder stones mechanically with an
instrument called lithotrite. This instrument is introduced into the bladder through the urethra. Laparoscopy - This is another kind of 'key hole' surgery to clear selected stones in the kidney or ureter.

Any patient who has had a symptom due to urinary stones (called a 'stone event') should have their blood and urine checked. This is in addition to the imaging investigations used to diagnose stones. A preliminary panel of investigations would give a clue to any metabolic condition that
predisposes to stone formation. If a stone is passed out through urine, this can be analysed to analyse the chemical composition of the stone which would give information regarding specific measures to prevent that kind of stones. In addition, many patients would require 24 hour urine
collection for analysis to have a detailed evaluation of metabolic abnormalities that can cause stones. Dietary modifications to prevent stones are aimed at the specific stone that is formed by a patient. This is done in consultation with a nutrition specialist too. Uric acid stones are prevented by avoiding food which are high in purine content viz animal protein. Oxalate stones would mandate restriction of leafy vegetables, nuts, chocolate, amla, grapes etc which are rich in oxalates.

Preventive measure for all kinds of stones would involve maintaining a high fluid intake. Fluid intake is maintained such that an average adult produces more than two litres of urine per day. However the amount of fluid required would depend on the body weight of the person also.
Intake of about 50ml per kg body weight would be required. The patient can easily self monitor the adequacy of fluid intake by watching the colour of urine. To prevent stone formation, urine should be dilute which is indicated by a colourless or pale yellow coloured urine. As regards management of urinary stones is concerned, it is always better to prevent stones rather that treating them after they are formed.

Dr. Renu Thomas
MBBS, MS (PGI), DNB, MCh
Consultant Urologist and Transplant Surgeon
KIMS, Thiruvananthapuram

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