Nephrolithiasis

Nephrolithiasis or renal stones is a very common disorder of the renal system. Different types of renal stones or calculi may form including calcium oxalate (most common), calcium phosphate, uric acid, cystine and struvite stones. Staghorn calculi are branched stones which extend into adjoining calyces. Struvite stones form staghorn calculi. Calcium oxalate stones start as deposits called Randall’s plaques in the loop of Henle. Calcium phosphate stones begin in the collecting ducts from crystal deposition. Patients with cystinuria are predisposed to form cystine stones. Rarely, insoluble drugs like indinavir, triamterene and ephedrine may form stones. It presents with renal colic starting in the flank and moving down to the genital area as the stone moves from the upper to the lower urinary tract. Pain is not affected by changes in body position. Nausea, vomiting, sweating, gross or microscopic hematuria, urinary urgency and frequency are also present. Symptoms are relieved once the stone passes out into the bladder and is passed in urine. Renal stones predispose to UTI. Distal renal tubular acidosis, hyperparathyroidism, hypercalciuria, hyperuricosuria, oxaluria and cystinuria are associated with recurrent stones. Excess Vit C and low calcium diet can cause hyperoxaluria. Myeloproliferative disorders or chemotherapy can cause hyperuricosuria. Calcium supplements increase the risk of stone formation, especially when taken on an empty stomach.

Preferred investigation is CT without contrast. KUB can be used to visualize radio-opaques stones only. Ultrasound is preferred as an initial investigation in children and pregnant women to avoid exposure to radiation. Stones > 10 mm in size do not pass spontaneously while most stones < 5 mm in size are passed spontaneously in urine. Patients should increase fluid intake to keep urine dilute. NSAIDS and narcotics are used to control pain. Thiazides help to prevent stone formation in patients with hypercalciuria, by increasing calcium absorption in the proximal tubule. Potassium citrate chelates calcium in urine and prevents calcium stone formation. Cholestyramine helps prevent oxalate stone formation. Drugs like doxazosin, tamsulosin, nifedipine help to pass stones < 10 mm. Extracorporeal shock wave lithotripsy or ESWL can be used to break down larger stones. Stones in the ureters and renal pelvis can be removed endoscopically by ureteroscopy. In the presence of hydronephrosis, immediate treatment is needed to preserve renal function. Stones can be studied by X-ray crystallography and infrared spectroscopy to suggest preventive measures.