Osteomalacia

Osteomalacia is a disease characterised by the softening of bones due to impaired bone metabolism, primarily caused by inadequate levels of phosphate, calcium, and vitamin D, or due to calcium resorption. This impairment results in inadequate bone mineralisation.

Osteomalacia in children is known as rickets, with the adult form often considered milder.

This condition is often marked by diffuse body pains, muscle weakness, and bone fragility.

Signs and Symptoms

The disease manifests with several symptoms, many of which overlap with osteoporosis, though they are distinct conditions. Common signs and symptoms include diffuse joint and bone pain, especially in the spine, pelvis, and legs, muscle weakness, and difficulty walking, often with a waddling gait. Other signs include hypocalcaemia (positive Chvostek sign), compressed vertebrae and diminished stature, pelvic flattening, weak and soft bones, easy fracturing, and bending of bones.

In adults, osteomalacia typically begins with aches and pains in the lower back and thighs, eventually spreading to the arms and ribs. The pain is symmetrical, non-radiating, and accompanied by sensitivity in the involved bones. Physical signs may include proximal muscle weakness, difficulty in climbing stairs, and getting up from a squatting position. Deformities such as triradiate pelvis and lordosis can occur due to demineralisation. A typical "waddling" gait may develop, and pathologic fractures due to weight bearing are common. Chronic fatigue may be the only symptom, with bone aches revealed only by pressure or shocks.

Causes

The primary cause of adult osteomalacia is a deficiency of vitamin D, which is very important for calcium and phosphate metabolism. Contributing factors include insufficient dietary intake, faulty metabolism of vitamin D or phosphorus, renal tubular acidosis, malnutrition during pregnancy, malabsorption syndrome, hypophosphataemia, chronic kidney failure, tumour-induced osteomalacia, long-term anticonvulsant therapy, celiac disease, and cadmium poisoning (itai-itai disease).

There are two main mechanisms for osteomalacia:

1. Insufficient calcium absorption from the intestine due to lack of dietary calcium, vitamin D deficiency, or resistance, often linked to undiagnosed celiac disease.
2. Phosphate deficiency caused by increased renal losses.

Diagnosis

Biochemical Findings

Biochemical features are similar to those of rickets, with the major factor being an abnormally low vitamin D concentration in blood serum. Key biochemical findings include low serum and urinary calcium, low serum phosphate (except in renal osteodystrophy), elevated serum alkaline phosphatase due to increased osteoblast activity, and elevated parathyroid hormone due to low calcium. A technetium bone scan will show increased activity due to increased osteoblasts.

Condition	Calcium	Phosphate	Alkaline phosphatase	Parathyroid hormone	Comments
Osteopenia	unaffected	unaffected	normal	unaffected	decreased bone mass
Osteopetrosis	unaffected	unaffected	elevated	unaffected	thick dense bones also known as marble bone
Osteomalacia and rickets	decreased	decreased	elevated	elevated	soft bones
Osteitis fibrosa cystica	elevated	decreased	elevated	elevated	brown tumours
Paget's disease of bone	unaffected	unaffected	variable (depending on stage of disease)	unaffected	abnormal bone architecture

Radiographic Characteristics

Radiological appearances can include pseudofractures (Looser's zones) and protrusio acetabuli, a hip joint disorder.

Prevention

Preventing osteomalacia primarily involves ensuring adequate intake of vitamin D and calcium. Vitamin D supplementation is often necessary, particularly due to the scarcity of vitamin D sources in the modern diet.

Treatment

Nutritional osteomalacia responds well to the administration of 2,000-10,000 IU of vitamin D3 daily. Vitamin D3 (cholecalciferol) is typically absorbed more readily than vitamin D2 (ergocalciferol). For osteomalacia due to malabsorption, treatment may require either injections or daily oral dosing of significant amounts of vitamin D3.

Etymology

The term "osteomalacia" is derived from the Greek words "osteo-" meaning "bone" and "malacia" meaning "softness". Historically, the disease was also known as malacosteon and its Latin equivalent, mollities ossium. Osteomalacia is associated with an increase in osteoid maturation time.

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Self-assessment MCQs (single best answer)

What is the primary cause of osteomalacia in adults?

Which of the following is NOT a common symptom of osteomalacia?

What is the term used for osteomalacia in children?

Which biochemical finding is elevated due to increased osteoblast activity in osteomalacia?

What kind of gait might develop in a person with severe osteomalacia?

Which of the following is a common radiographic characteristic of osteomalacia?

Which of the following conditions is characterised by decreased bone mass but normal biochemical findings?

Which hormone is typically elevated in osteomalacia due to low calcium levels?

What type of vitamin D is typically absorbed more readily for the treatment of osteomalacia?

What is the etymological meaning of the term "osteomalacia"?