A 58 year man presented with multiple rib and vertebral fractures secondary to minor trauma. His Bone Mineral density ( BMD) in August 2018 showed severe osteoporosis with a femoral neck T score of -4.22 and lumbar spine T score of -2.04.
His secondary screening showed borderline low testosterone at 9.0nmol/L ( 9-35nmol/L) and low normal FSH of 4.6U/L and LH 3.5U/L. His prolactin was elevated at 6420mU/L (56-278mU/L) which was more than 10 times the upper limit of normal. He subsequently underwent an MRI of his pituitary which showed a 15mm macroprolactinoma
He was commenced on cabergoline 0.25mg twice weekly and Alendronate weekly. His prolactin levels normalized to 17mU/L and his testosterone improved to 13nmol/L.
Hyperprolactinaemia is an unusual cause of secondary osteoporosis in men. The pathogenesis is uncertain. It is unclear whether prolactin directly enhances bone loss or it is mediated by hypogonadism. In females the incidence of secondary osteoporosis correlates with amenorrhoea. However one small study that included male patients with prolactinomas showed no association between the incidence of osteoporotic fractures and serum testosterone levels, suggesting that prolactin has direct effect on bone loss.
Management includes normalization of prolactin levels. However normalization of prolactin is inadequate to correct the osteoporosis. One study showed that despite correction of hyperprolactinaemia and normalization of gonadal function bone density improvement was minimum. Therefore treatment in these patients should not only include dopamine agonists but also antiresorptive agents to improve fracture risk.