Metabolic Bone Disease (Osteoporosis and Osteomalacia)

Key points

• • Metabolic bone diseases weaken the whole skeleton by upsetting bone turnover or its mineral content, unlike a local problem such as a tumour.
• • Osteoporosis is a loss of bone mass with normal mineralisation, so the bone is normally mineralised but reduced in amount and weakened in its microarchitecture, and it breaks easily.
• • Osteoporosis is commonest after the menopause (from falling oestrogen) and in old age, and it typically causes fractures of the hip, wrist and spine.
• • Osteomalacia is poor mineralisation of the bone from a lack of vitamin D or calcium, so the bone is soft; in growing children the same problem causes rickets.
• • In osteoporosis the blood calcium and phosphate are usually normal, whereas in osteomalacia the vitamin D is low with a low or normal calcium, often a low phosphate and a raised alkaline phosphatase.
• • In Paget disease of bone, by contrast, bone is broken down and rebuilt too fast, giving thick but weak and misshapen bone.