Metabolic bone disease in long-term HPN in adults

Patients on long-term HPN are at risk of developing metabolic bone disease (MBD), with a significant reduction in bone mineral density (BMD) and osteoporosis in about half of them. The MBD is often asymptomatic. Bone pain, mainly at spine and lower joints, has been reported in one third of patients and bone fractures in one tenth. In most of the cases, the MBD is due to general factors, like aging and postmenopausal status, or to causes related to the patient’s underlying illness (HPN-associated MBD), which are already present before starting the HPN program. Follow up studies indicate that long-term HPN is not necessarily associated with a worsening of bone health and in some cases an improvement occurs. Nevertheless, accelerated bone loss may occur during the HPN therapy, raising the question of a specific role of HPN in the pathogenesis of the MBD (HPN-related MBD). Hypercalciuria due to iv nutrient loads (excess of amino acids, calcium, sodium, glucose; deficiency of phosphate; non appropriate Ca : P molar ratio in the PN solution; excess of fluids), iv vitamin D poisoning, micronutrient deficiency deficiency or toxicity (vitamin K, vitamin C, zinc, copper, floride, boron and silicon deficiency; vitamin A, cadmium, aluminium and strontium toxicity), HPN induced impaired PTH secretion/function and/or secretion of proinflammatory cytokines are the suggested HPN-related pathogenetic factors. Diagnosis and monitoring rely on BMD and assessment of biochemical markers of bone turnover; this should be performed when starting HPN, then yearly if patients remain in stable condition. The bone turnover should also be evaluated if long lasting changes of the clinical condition occur. Prevention and treatment are based on life-style and dietary recommendations, active treatment of the underlying disease related-factors and on optimisation of the parenteral solution. A few studies have shown that iv bisphosphonates may prevent further bone demineralisation in patients on HPN. No studies with other drugs for osteoporosis have been carried out on these patients