8: Disorders of bone and mineral other than osteoporosis.

Rickets in children and osteomalacia in adults are caused by undermineralisation of bone, which increases its susceptibility to bending and fracture; treatment is with calcium, vitamin D or phosphate, depending on the specific mineral or vitamin deficiency. In Paget's disease, osteoclasts are overactive and produce woven or "repair" bone, which is mechanically weaker than lamellar bone; treatment is with antiresorptive bisphosphonate drugs. Cancers can produce bone lysis through direct spread within the skeleton or production of endocrine parathyroid hormone-like factors; treatment is with a bisphosphonate, plus appropriate therapy for the cancer. Cancer can also produce hypercalcaemia if the capacity of the kidneys to excrete the calcium dissolved from bone is exceeded; treatment is with saline infusion to increase excretion and a bisphosphonate. Primary hyperparathyroidism is the other common cause of hypercalcaemia and is usually associated with a single parathyroid adenoma; it is best treated with parathyroidectomy. Hypocalcaemia may result from severe decrease in calcium absorbed or lack of parathyroid action; both are treated with calcium and vitamin D (ergocalciferol or calcitriol). These disorders range from nutritional deficiencies to complex genetic and metabolic diseases