Changes in calcium metabolism and bone demineralization after orthotopic intestinal neobladder creation

We evaluated calcium metabolism and bone demineralization by measuring specific markers for bone reabsorption and bone mineral density in patients with an intestinal neobladder.

We studied 33 men 55 to 72 years old who underwent creation of an orthotopic sigmoid (23), ileocolic (8) or ascending colon (2) neobladder after cystectomy. Mean followup plus or minus standard deviation (SD) was 28.4+/-30.1 months (range 4 to 114). Serum electrolytes and arterial blood gases were measured. As markers of bone absorption we assayed urinary pyridinoline, deoxypyridinoline and N-terminal pyridinoline cross-linked telopeptides, and serum pyridinoline cross-linked C-terminal telopeptide of type I collagen. Bone mineral density of the spine and femur was determined by dual x-ray absorptiometry.

Mean blood pH plus or minus SD was 7.38+/-0.04 (range 7.29 to 7.43). Mean plasma bicarbonate was 22.9+/-3.4 mmol./l. and mean base excess was -1.63+/-3.61 mmol./l. Serum sodium, potassium, calcium, alkaline phosphatase and phosphate were normal in most patients. Mean serum chloride was 108.0+/-3.5 mEq./l., and was elevated in 9 of the 33 patients (27.3%). Serum intact parathyroid hormone was normal in all patients, osteocalcin was increased in 2 and 1alpha, 25-dihydroxyvitamin D3 was decreased in 2. Pyridinoline cross-linked C-terminal telopeptide of type I collagen was higher in 19 of 33 cases (57.6%) and N-terminal pyridinoline cross-linked telopeptides were elevated in 6 (18.2%). Pyridinoline and deoxypyridinoline were higher than normal in 19 (57.6%) and 7 (21.2%) patients, respectively. C-terminal telopeptide of type I collagen and deoxypyridinoline significantly correlated with serum pH (p = 0.017 and 0.0418, respectively). Z score for the bone mineral density of L2 to L4, the femoral neck and Ward's triangle was -0.350+/-1.031, -0.82+/-0.99 and -0.94+/-1.01, respectively.

In patients with a neobladder of intestinal segments metabolic acidosis results in increased bone absorption and decreased bone mass. Thus, attention should be given to bone metabolism in patients with even mild acidosis after orthotopic neobladder creation.