Kidney stones, or renal calculi- Case analysis

QUESTION

Fred, a fit and healthy 44-year-old, was working outside one warm summer afternoon. When he returned home by the end of the day, his lower back felt sore and he felt nauseated. His wife made him dinner, but he was not hungry and chose to go to bed instead. Fred’s symptoms progressed, and soon he was rolling on the bed with excruciating pain. He said his back hurt as well as his stomach and groin area. The pain would ease off only to return a short while later, and when it did, Fred would begin to sweat and run to the bathroom to vomit. His wife became concerned and started the car. When his symptoms abated, she helped him into the car and rushed him to the hospital.

1. At the hospital, an abdominal radiograph showed the presence of renal calculi in Fred’s right ureter (urolithiasis). What is the mechanism of stone formation in the kidney? What is the role of citrate in the kidneys?
2. Why would the administration of calcium supplements be useful for a patient with calcium oxalate stones?
3. Hydronephrosis can be a complication of renal calculi. What is hydronephrosis? How does back pressure occur in a kidney, and what physiologic mechanism is responsible for nephron damage when back pressure is present

ANSWER

Kidney stones, or renal calculi, are formed when certain substances in the urine, such as calcium, oxalate, and uric acid, crystallize and clump together to form solid masses. The mechanism of stone formation in the kidney involves a complex interplay between various factors. The urine normally contains substances that help prevent the formation of stones, such as citrate. Citrate acts as an inhibitor of stone formation by binding to calcium ions and preventing their aggregation. It also helps to maintain urine pH at levels that discourage stone formation.

In the case of calcium oxalate stones, the administration of calcium supplements can be beneficial. This may seem counterintuitive since calcium is a component of the stones, but the rationale behind it is based on the concept of “intestinal binding.” When calcium is ingested along with a meal, it binds to oxalate in the intestines and prevents its absorption into the bloodstream. This reduces the amount of oxalate available for excretion in the urine, thereby lowering the risk of calcium oxalate stone formation.

Hydronephrosis is a condition characterized by the swelling of the kidney due to the accumulation of urine in the renal pelvis and calyces. It can be a complication of renal calculi if the stone obstructs the flow of urine. Back pressure occurs in the kidney when the normal flow of urine is obstructed, leading to a buildup of urine behind the obstruction. The physiologic mechanism responsible for nephron damage in the presence of back pressure is related to increased intraluminal pressure within the nephron. This pressure can compress and damage the delicate structures of the nephron, impairing its function and potentially leading to kidney dysfunction if left untreated.

In conclusion, the formation of kidney stones involves the crystallization and clumping together of certain substances in the urine. Citrate plays a role in inhibiting stone formation. Calcium supplements can be beneficial in preventing calcium oxalate stones by promoting intestinal binding of oxalate. Hydronephrosis is a potential complication of renal calculi due to urinary obstruction, which can result in back pressure and damage to the nephron. Understanding these mechanisms is crucial for effective management and prevention of kidney stone-related complications.