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Metabolic Bone Disorder (Osteomalacia)

Metabolic Bone Disorder (Osteomalacia) Metabolic Bone Disorder (Osteomalacia)

What is osteomalacia?

Osteomalacia is a metabolic bone disease that results from under mineralisation of bone. Bone has two components: matrix and mineral. Matrix forms 70% of the composition of bone and the remaining 30% is formed by minerals. The predominant mineral in bone is called calcium hydroxyapatite. The calcium in bone is actually deposited from the calcium that is available in the blood. If the calcium in the blood is low as well as phosphorus the deposition of calcium hydroxyapatite in bone is affected. This is known as osteomalacia.

What are the risk factors of osteomalacia?

 

Risk factors for osteomalacia include: 

  • Chronic vitamin D deficiency.
  • Chronic dietary deficiency of calcium 
  • Chronic kidney disease
  • Certain chronic drug therapies

Osteoporosis refers to a condition where both the Matrix and mineral are reduced equally. Osteoporosis results from lesser formation of Matrix but the Matrix that is formed is normally mineralised. Since there is less amount of Matrix available per volume of bone, the mineral is also reduced. Therefore when we do a bone densitoMetry, the BMD will be equally reduced in both osteomalacia osteoporosis.  Distinction between these two entities is done by analysis of patient symptoms, looking for certain signs and blood tests. In osteomalacia usually there will be blood test abnormalities of calcium, phosphorus or both. Alkaline phosphatase may be elevated in osteomalacia.

What is the Normal level of Vitamin D?

Normal level of vitamin D is more than 30 ng/dL. 20 to 30 ng/dL is considered insufficient. Less than 10 ng/dL is considered severe deficiency. 

If osteomalacia is left untreated, the patient continues to have severe bone pains and also muscle weakness limiting his mobility. In severe cases fractures may result leading to immobilization and further worsening of osteomalacia.

How is osteomalacia diagnosed?

Osteomalacia can be presumptively diagnosed through a combination of symptoms signs and blood test abnormalities of calcium phosphorus alkaline phosphatase. In nutritional osteomalacia vitamin D can be very low and is helpful in making a diagnosis. Definitive diagnosis requires a bone biopsy. 

How is osteomalacia treated?

Osteomalacia due to vitamin D deficiency is easily treated with oral vitamin D supplementation which is to be given every week for 2 to 3 months. After this period of loading dose vitamin D is then administered monthly to maintain levels in blood.

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