There are mainly four types of kidney stones, calcium oxalate, uric acid, calcium pyrophosphate and cystine. Passing a kidney stone is very painful. This is generally severe, comes and goes, starts in the flank and radiates to the front. It is known as renal colic. Renal colic occurs when the stone is in the ureter, pressing against the sensitive ureter walls. Often times, urologists can remove the stones before they pass, and in many instances, the nephrologist can analyze the kidney stone and help prevent its recurrence or even dissolve it using medications and dietary adaptation. Whether to manage a kidney stone medically or using an intervention has been discussed by the American Urological Association. The AUA reviewed 1,911 articles when issuing their 2016 guideline statements (http://www.auanet.org/guidelines/surgical-management-of-stones-(aua/endourological-society-guideline-2016)#x3169). Medical management is prudent for smaller stones, those less than 8-10 mm, as many can pass spontaneously, or with the use of medical expulsive therapy. The meta-analysis that was done by the American and European urological associations identified that when stones were ≤ 5 mm, 68% pass spontaneously. When stones are > 5 mm and ≤ 10 mm, 47% pass spontaneously.
Reference: Preminger GM, Tiselius HG, Assimos DG, Alken P, Buck C, Gallucci M, Knoll T,
Lingeman JE, Nakada SY, Pearle MS, Sarica K, Türk C, Wolf JS Jr; EAU/AUA
Nephrolithiasis Guideline Panel. 2007 guideline for the management of ureteral
calculi. J Urol. 2007 Dec;178(6):2418-34. Review. PubMed PMID: 17993340.
Active surveillance is appropriate for patients who are asymptomatic, but clinicians may offer stone treatment for patients who are symptomatic with flank pain. 95% of stones > 8 mm require intervention by a urologist.
Terminology associated with kidney stones:
SWL – shockwave lithotripsy
URS – ureteroscopic lithotripsy
PCNL – percutaneous nephrolithotomy
MET – medical expulsive therapy
Calcium oxalate stones – These are most common and occur when one drinks inadequate fluids, eats excess protein or salt, or a diet high in foods containing excessive oxalate. Persons with colitis may also have increased oxalate absorption. Stones occur when their is too little fluid in the kidney environment to keep salts from forming crystals. Excess oxalate containing foods include nuts, beets, soy, bran, and Swiss chard. Persons should not avoid oxalate containing foods altogether. It is not necessary. Vitamin C can also potential oxalate stones. These can be prevented by adequate hydration, the use of potassium citrate (that helps dissolve stones) and sometimes thiazides diuretics (that potential calcium reabsorption.
Uric acid stones – These stones may not appear on a plain film, but will be detectable on a renal ultrasound. They can occur when the uric acid is high and in the presence of an acidic urine. Persons with gout may have a higher incidence of uric acid stone. They can be dissolved in many cases. Using conventional medical therapy- alkalization of the urine, encouraged hydration and an xanthine oxidase inhibitor such as allopurinol, it may take several months for a uric acid stone to dissolve.
Struvite stones – This is less common than uric acid or calcium oxalate as the cause of kidney stones. Struvite refers to a mineral made by bacteria, and these hard, large stones are caused by bacterial infections. They may encompass the entire renal pelvis, forming what is referred to as staghorn calculi. They are associated with an alkaline urine, hence acidification of the urine is optimal. These stones may require more than medical management.
Cystinuria – This is extremely rare because it is an autosomal recessive disorder. It is a genetic diorder where cysteine can accumulate in the kidney and form stones. The child must inherit a copy of the gene from both parents to develop the disease. There is no treatment for cystinuria.
