Osteomalacia - Metabolic bone disorders

Osteomalacia

Definition

Inadequate mineralisation of growing bone. In adults decreased mineralisation causes osteomalacia, and in children it results in rickets.

Aetiology

Osteomalacia is usually due to a lack of vitamin D or its active metabolites, but it may be caused by severe calcium deficiency or by hypophosphataemia.

Pathophysiology

During bone remodelling vitamin D deficiency results in a failure of calcification of new bone. This causes weakness of the bone and an increased risk of fractures.

Clinical features

Onset is insidious with bone pain, backache and weakness that may be present for years before the diagnosis is made. Vertebral compression and pathological fractures may occur; a biochemical diagnosis may be made prior to onset of clinical disease.

Investigations

X-ray investigation shows generalised bone rarefaction and possible evidence of fractures. Looser’s zones may be seen in which there is a band of severe rarefaction surrounded by sclerosis due to failed healing of a fracture.

Serum calcium and phosphate levels are generally low

with raised alkaline phosphatase. Serum 25-hydroxy vitamin D3 levels are low.

Investigation for an underlying cause such as malabsorption or renal disease should be performed.

Management

Treatment is aimed at the underlying disorder but often involves oral calcium and vitamin D replacement.