Disorders of bone mineralization—osteomalacia

Disorders of bone mineralization cause rickets in children and osteomalacia in adults. Both remain common in developing countries. Incidence in Western countries had declined since the fortification of foodstuffs, but appears to be increasing again. Calcium and inorganic phosphate are the key precursors for bone mineralization and growth. The commonest aetiology of osteomalacia is vitamin D deficiency, primarily due to low dietary intake and inadequate sun exposure. In the last decade gene mutations have been identified that are responsible for inherited rickets and osteomalacia, particularly those that result in phosphate deficiency, hypophosphatasia, and vitamin D receptor or metabolizing enzyme mutations. Additionally, the pathogenesis of tumour-induced osteomalacia is becoming better understood. Osteomalacia may present as bone pain and tenderness, muscle pain and weakness, and skeletal deformity or fracture. Key investigations include biochemical assessment and plain radiographs. Radioisotope bone scans and bone biopsy may be considered in selected cases. Differential diagnoses include osteoporosis, seronegative arthritides, and localized soft tissue disorders. Treatment, guided by the underlying aetiology, aims to reduce symptoms, fracture risk, bone deformity and sequelae. Vitamin D deficient patients require vitamin D and calcium replacement.