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

Purpose: We evaluated calcium metabolism and bone demineralization by measu ring specific markers for bone reabsorption and bone mineral density in pat ients with an intestinal neobladder. Materials and Methods: We studied 33 men 55 to 72 years old who underwent c reation of an orthotopic sigmoid (23), ileocolic (8) or ascending colon (2) neobladder after cystectomy. Mean followup plus or minus standard deviatio n (SD) was 28.4 +/- 30.1 months (range 4 to 114). Serum electrolytes and ar terial blood gases were measured. As markers of bone absorption we assayed urinary pyridinoline, deoxypyridinoline and N-terminal pyridinoline cross-l inked telopeptides, and serum pyridinoline cross-linked C-terminal telopept ide of type I collagen. Bone mineral density of the spine and femur was det ermined by dual x-ray absorptiometry. Results: 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 pho sphatase and phosphate were normal in most patients. Mean serum chloride wa s 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 wa s increased in 2 and l alpha, 25-dihydroxyvitamin D3 was decreased in 2. Py ridinoline cross-linked C-terminal telopeptide of type I collagen was highe r in 19 of 33 cases (57.6%) and N-terminal pyridinoline cross-linked telope ptides mere elevated in 6 (18.2%). Pyridinoline and deoxypyridinoline were higher than normal in 19 (57.6%) and 7 (21.2%) patients, respectively. C-te rminal telopeptide of type I collagen and deoxypyridinoline significantly c orrelated with serum pH (p = 0.017 and 0.0418, respectively). Z score for t he bone mineral density of L2 to L4, the femoral neck and Ward's triangle w as -0.350 +/- 1.031, -0.82 +/- 0.99 and -0.94 +/- 1.01, respectively. Conclusions: In patients with a neobladder of intestinal segments metabolic acidosis results in increased bone absorption and decreased bone mass. Thu s, attention should be given to bone metabolism in patients with even mild acidosis after orthotopic neobladder creation.