Osteomalacia & rickets
In osteomalacia there is a normal boney matrix which is undercalcified. Rickets is the clinical sign of deformation at the boney epiphyses if calcium deficiency occurs during bone growth. Osteomalacia is the clinical description of signs that occur after epiphyseal closure. The symptoms of both are: bone pain, fractures and proximal myopathy. "Looser's" zones are seen on x-ray and there is loss of cortical bone.
In cases due to abnormalities of vitamin D, there is hypocalcaemia due to low vitamin D and secondary hyperparathyroidism. This is turn causes an increase in renal excretion of phosphate and reduced loss of calcium in the urine. There causes hypophosphataemia and a raised alkaline phosphatase due to increased osteoblastic activity.
Causes of osteomalacia
- Malnutrition due to poor diet of calcium, phosphate and/or vitamin D
- Malabsorption of calcium, phosphate and/or vitamin D due to gastrointestinal disease
- Poor synthesis of vitamin D due to liver or renal failure ie failure of 1a-hydroxylation of vitamin D3 or, rarely, inadequate sunlight.
- Increased inactivation of vitamin D by anticonvulsants
- Vitamin D resistance syndromes (rare)
- Renal tubular loss of phosphate due to X-linked hypophosphataemic rickets, tumour-induced phosphaturia and miscellaneous causes eg renal tubular acidosis and Fanconi syndrome.