Kidney stone disease

Kidney stone disease, also called nephrolithiasis or urolithiasis, refers to the presence of kidney stones in the urinary tract. When stones are present in the ureter it may be called ureterolithiasis, while stones in the bladder are usually simply called bladder stones or bladder calculi. It's a relatively common condition, with a lifetime prevalence of 10 - 20 percent.

Many have asymptomatic kidney stones, but these stones can cause urinary obstruction (obstructive uropathy) and resulting damage to the kidney, as well as episodes of severe pain.

Pathology

Kidney stones are usually small (2-3 mm). 80% of kidney stones are formed of calcium oxalate. 10% are so-called struvite stones, which are formed of magnesium ammonium phosphate. The remaining types are formed of uric acid and cysteine.

Stone formation occurs when the urine is supersaturated with the components of the stone. In some cases other factors will contribute to the formation of stones as well, like abnormal pH.

Struvite stones occur in people with alkaline urine. Alkaline urine is a result of a urinary tract infection, especially one caused by bacteria that produce urease, like Proteus and Staphylococcus. Struvite stones can sometimes make a “cast” of the renal pelvis, called staghorn calculi.

Uric acid stones occur in people with acidic urine and increased excretion of uric acid. The latter can be idiopathic or in combination with gout or diseases that cause rapid cell turnover, like leukaemia.

Cysteine stones occur in people with genetically determined defects in renal transport of cysteine. Acidic urine also increases the risk for cysteine stones.

The pain associated with kidney stones is thought to occur due to distension of the kidney capsule due to urinary obstruction and due to ureteric spasm.

Clinical features

Kidney stones may be asymptomatic, especially if they are in the renal pelvis.

Renal colic

When a kidney stone passes from the renal pelvis into the ureter, it may get stuck. This causes episodes of severe flank pain. This pain is typically colicky, meaning that it starts and stops abruptly. There may be visible haematuria. The pain may radiate to the ipsilateral testicle or labium. The patient usually has a severe urge to move.

Other pain

A kidney stone may also present with pain other than renal colic. Pain may be mild and not localised to the flank. In these cases, the diagnosis is difficult.

Diagnosis and evaluation

A presumptive diagnosis may be made when the patient has typical renal colic, as kidney stone is highly likely in that case.

Haematuria on urine analysis is seen in most cases of kidney stone (90%), but absence of haematuria does not exclude the diagnosis.

Imaging

A low-dose non-contrast CT is usually the first choice as this has little radiation exposure and can detect the majority of stones. Ultrasonography is a reasonable alternative first choice, especially in pregnant and children, but many stones are not visible on ultrasound (70% sensitive and specific). Kidney, ureter, bladder (KUB) radiography was previously widely used, but it is not sensitive and so is rarely used nowadays.

If the stone causes urinary obstruction, one may see hydronephrosis and dilated proximal ureters.

Management

Asymptomatic stones need no management or follow-up.

Renal colic

An NSAID like ketorolac or diklofenac is the best first choice for renal colic. In addition to relieving pain they also decrease ureteral smooth muscle tone. Hydration, preferably intravenous, is important.

An alpha blocker like tamsulosin may be administered as it may fascilitate passage of the stone.