Ammonium acid urate stones derived from laxative abuse
Eating disorders, such as anorexia nervosa and bulimia nervosa are very common. These eating disorders are known to be associated with kidney stones.
In anorexia, the person has an intense fear of gaining weight and limits the food they eat. Eighty-five to ninety-five percent of these individuals are female and 1–4.2 % of women suffer from anorexia in their lifetime . As a result of this disorder, fasting, vomiting and purging result in loss of fluids and minerals. The chronic dehydration and low potassium levels can lead to kidney stones and even renal failure. In anorexia nervosa, nephrolithiasis are composed most frequently of ammonium urate due to low urinary output and increased urinary ammonium output secondary to low urinary phosphate and diarrhea with hyperchloremic metabolic acidosis. Low urine output leading to high urinary uric acid, oxalate and calcium can lead to uric acid and calcium stones as well as nephrocalcinosis .
Bulimia is characterized by enormous consumption of food, followed by self-induced vomiting. Eighty-five to ninety percent of individuals with bulimia are women. Up to 4 % of females in the United States will have bulimia in their lifetime . The individuals alternate between eating and purging. Urinary Calcium and Oxalate levels rise during eating and drop during the fasting phase.
In treating patients with eating disorders who make stones, the first issue is to address the underlying disease. These patients first need to address their eating disorder. Treating this may correct the risk of stones. Since eating disorders may be a life threatening condition, patients are encouraged to address this issue first. The psychological issues of this disorder are beyond the scope of this discussion.
Crohn’s disease is an inflammatory bowel disease that results in inflammation of the lining of the digestive tract. It affects men and women equally. In this disease, fat binds to calcium, leaving oxalate free to be absorbed and deposited in the kidney, where it can bind with calcium to form a stone. Their urine is more concentrated, a condition that is more likely to lead to stone formation. The risk of stones is greater than the general population and these individuals usually produce calcium oxalate stones . Kidney stone treatment calls for an increased fluid intake together with a low-oxalate diet.
Patients with Crohn’s disease are also at risk for forming uric acid stones. This type of stone develops in acidic urine and this is caused by increased uric acid absorption in the injured colon. These patients can be treated with potassium citrate.
There is a higher prevalence of osteoporosis and a greater incidence of fractures in postmenopausal women than older men . Osteoporosis is often referred to as a “woman’s disease”. Gender is a risk factor for osteoporosis and may be a risk factor for stones.
Women with a history of kidney stones may be at a greater risk of developing coronary heart disease . This association or increased risk was not found in men. A possible explanation for this distinction may be hormonal differences between men and women.
Gender and Anatomical Barriers for Stones
The ureter has three anatomical narrowed areas along it’s course from the kidney to the bladder. First is the ureteropelvic juncture (or UPJ); the second area is the crossing iliac vessels; the third area is the ureterovesical juncture (or UVJ). These anatomical barriers for blocking the passage of a stone exist in both men and women.
In men with enlarging prostates, they may have an additional barrier that may prevent the passage of stones.
Gender and age are the two highest risk factors for bladder stones. Ninety-five percent of the individuals who develop bladder stones are men. Middle-aged men over the age of 50 have the greatest risk of developing bladder calculi. An enlarged prostate, referred to as benign prostatic hyperplasia (BPH), is a major risk factor for bladder stones in men. As the prostate grows, it interferes with the flow of urine resulting urine to be retained within the bladder.
Five percent of all bladder stones occur in women. These stones are usually associated with calcifications of foreign bodies (synthetic material) within the bladder, such as sutures, synthetic tapes or meshes .
Gender Hormones and Stones
Male stone former were found to have higher serum total testosterone than men without stones . This suggests that testosterone may be a lithogenic factor for stone disease.
Female hormones (estrogens) actually lower the risk of hyperoxaluria. Estrogen may help prevent the formation of calcium oxalate stones by keeping urine alkaline, and by raising protective citrate levels.
Gender and Stone Risk Factors
Obesity and weight gain can increase the risk of stone formation. Men and Women weighing more than 220 lb were 44 and 90 %, respectively, more likely to develop stone disease than women weighing less than 150 lb. Both men and women who gained more than 35 lb after 21 years of age were 39 and 82 %, respectively, more likely to develop calculi than individuals who did not gain weight. The magnitude of this increased stone risk may be greater in women than in men .
Obesity is one of the major factors that increase the risk of nephrolithiasis in postmenopausal women. Eating more than 2,200 cal per day could increase the risk for nephrolithiasis by up to 42 % . Exercise was shown to reduce the risk of stones. See Chap. 13 for more information on obesity and stones.
Gender Factors and Stones
During pregnancy, there are physiological changes that occur which may influence a woman’s chances of developing stones. Overall, the risk of developing stones during pregnancy is 1 in 1,500, which appear to be a similar occurrence to non-pregnant women .
Factors that increase the risk of stones:
The intestines absorb additional calcium and more is released into the urine.
The kidney and ureters become dilated due to increased levels of progesterone, especially on the right side due to compression fetus against the upper urinary tract. This results in slower delivery of urine and a greater risk of infection and stone formation.
Factors that decrease the risk of stones:
There is an increase of urinary citrate, which is an inhibitor of stone formation.
There is an increase in the filtration activity by the kidneys.
Stones formed during pregnancy are more commonly of the calcium phosphate  variety compared to the more common calcium oxalate stones formed by the general population. This may be indicative of the physiologic changes taking place during pregnancy. See Chap. 11 for additional information on pregnancy and stones.
The incidence of stones increases after menopause in women. Menopause is associated with an increased excretion of urinary calcium [23, 24], which may enhance the risk for calcium stones.
Studies demonstrate that men younger than their mid forties who underwent vasectomies had twice the risk for nephrolithiasis than their peers who did not have a vasectomy . The risk for stones persisted for up to 14 years after the procedure. Men who undergo vasectomies are encouraged to drink fluids to minimize this risk.