Osteomalacia involves softening of the bones caused by a deficiency of vitamin D or problems with the metabolism of this vitamin.
Osteomalacia means soft bones. Like osteoporosis, osteomalacia weakens the bones and makes bones more likely to break. However, the process is different from that in osteoporosis. In osteoporosis, bone is broken down faster than it is re-formed. In osteomalacia, the two activities are balanced, but the bone that is formed does not become dense and hard (mineralized).
Rickets and Osteomalacia
Cause of Osteomalacia
Osteomalacia has been associated with many mesenchymal tumours which are believed to produce a humoral factor 'phosphatonin' which increases phosphate excretion. Treatment of the tumour results in remineralization. Cause of Osteomalacia
Vitamin D deficiency is usually due to inadequate sunlight exposure, particularly in Asian women in Western countries whose clothing covers their skin, and whose diet may contain only small amounts of vitamin D. The elderly who are immobile and housebound similarly are not exposed to sunlight. Anticonvulsant therapy may affect vitamin D metabolism; these drugs are also toxic to osteoblasts. Malabsorption of vitamin D rarely occurs in gastrointestinal disease.
Chronic renal failure results in reduced 1a-hydroxylation of 25-(OH)D 3 . Mutations in the p 450c1 a gene (chromosome 12) cause 1a-hydroxylase deficiency, also known as vitamin D-dependent rickets type I , an autosomal recessive disease. In type II vitamin D-dependent rickets there is a defect in the intracellular 1,25-(OH) 2 D 3 receptor. X-linked hypophosphataemic rickets resulting in lower-limb deformities and stunted growth rate in affected males is caused by mutations in the PEX gene. In the Fanconi syndrome and in renal tubular acidosis, osteomalacia can develop, mainly because of the continuous phosphaturia.
Symptoms and clinical features of Osteomalacia
Adult osteomalacia may produce vague symptoms of bone or muscle pain and tenderness. Fractures are rare and usually asymptomatic. Occasionally a marked proximal myopathy leads to a characteristic 'waddling' gait. Deformity is uncommon. In modern practice many cases are detected biochemically in high-risk patients, especially those with gastrointestinal disease or surgery, before clear symptoms are present. Occasionally, tetany or other hypocalcaemic features may occur.
Prevention and Treatment of Osteomalacia
Health education to ensure a balanced diet, adequate exposure to sunlight and, where appropriate in high-risk individuals or communities, dietary vitamin D supplementation are all important aspects of prevention.
Treatment should be directed towards correction of the cause where possible, with increase in dietary vitamin D intake and sunlight exposure.