Curriculum · Musculoskeletal / Orthopedic / Rheumatology
Osteomalacia
What it is
Osteomalacia and rickets are both disorders of bone mineralization. Which part fails is what tells them apart.
- In osteomalacia the remodeling of preexisting bone is defective. It can affect individuals of any age and usually presents with bone pain and tenderness.
- In rickets the formation of new bone is defective. It can only occur in children with open growth plates, and presents with bone deformities and impaired growth.
So vitamin D deficiency in a child gives rickets, and in an adult gives osteomalacia.
Causes and risk
The causes are insufficient calcium, phosphate depletion, and direct inhibition of bone mineralization. The most common cause of both disorders is vitamin D deficiency, and a low serum phosphate by itself gives bone loss with osteomalacia in adults and rickets in children. Renal phosphate loss is another cause:
- Fanconi syndrome, a generalized dysfunction of the proximal renal tubules with impaired reabsorption of glucose, amino acids, phosphate, bicarbonate, uric acid and potassium. Inherited: cystinosis, the most common in children, Wilson disease, galactosemia and glycogen storage diseases. Acquired: drugs such as Ifosfamide, Tenofovir, Cisplatin and outdated tetracyclines, multiple myeloma, and heavy metal toxicity from lead or cadmium.
- Proximal type II renal tubular acidosis, with vitamin D-resistant hypophosphatemic rickets or osteomalacia with short stature and polyuria.
Malabsorption and vitamin deficiency are a further cause: in the middle-aged female with fatigue, pruritus and obstructive jaundice, of whom about 30% are asymptomatic, the complications include metabolic bone disease with osteoporosis, malabsorption, vitamin deficiency, hypercholesterolemia, hypothyroidism and anemia. The list of causes of Fanconi syndrome is given elsewhere as cystinosis, the most common in children, Sjogren's syndrome, multiple myeloma, nephrotic syndrome and Wilson's disease, and the disorder itself as a generalised reabsorptive disorder of renal tubular transport in the proximal convoluted tubule giving type 2 proximal renal tubular acidosis, polyuria, aminoaciduria, glycosuria, phosphaturia and osteomalacia.