Overview of kidney stones
Stone formation or their presence in the kidney is called “nephrolithiasis.” It is a result of crystallization of specific minerals which come out of solution (the urine) and clump together (aggregation). Nephrolithiasis causes mechanical blockage at its site in the urinary tract, but also acts as a foreign body that, with the stasis of urine collecting proximal to it, can create an ideal environment for infection.
Types of Stones
- Calcium stones: Calcium oxalate or calcium phosphate. Calcium stones are due to high levels of calcium in the blood (hypercalcemia, hyperparathyroidism), excess filtration of calcium into the urine such as in inflammatory bowel disease, a persistent alkaline pH of the urine which enhances crystallization, or a low urine output which concentrates all stone-making elements.
- Uric acid stones: From persistent hyperacidic urine (pH <5) or from uric acid overproduction and excretion.
- Cystine stones: From a genetic recessive disorder (cystinuria).
- Struvite stones: Magnesium ammonium phosphate stones due to infections with certain bacteria (Proteus or Klebsiella).
Signs and Symptoms
Signs (objective findings) include hematuria on urinalysis and stones identified on X-ray or ultrasound.
Symptoms (subjective complaints) include severe, migrating unilateral flank pain due to stone migration down the ureter, or back pain with stone(s) lodging in the kidney causing backup pressure from accumulating urine that cannot exit to the ureters.
The pain is intermittent in its severity, as the ureters have peristalsis which moves the urine toward the bladder or, in the case of a stone, moves a stone down the same path, distending the walls of the ureter (which are very sensitive to distention) in waves. The pain can also be all along the blocked portion of the ureter, up the flank to the back on one side, due to urine distending the ureter all the way up to the kidney (“hydronephrosis”).
The severity of pain is excruciating and debilitating, with patients often reporting pain scores of 9-10/10.