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Osteomalacia
Osteomalacia and Vitamin D Written by: Dr Sharon Cowley; Rheumatology Specialist Registrar, Mater Misericordiae University Hospital and Professor Gerry Wilson; Consultant Rheumatologist, Mater Misericordiae Hospital, St Vincent’s University Hospital, Conway Institute of Biomolecular & Biomedical Research, UCD.
Dr Sharon Cowley
Professor Gerry Wilson
SUMMARY: Osteomalacia is a metabolic bone disease characterised by impaired bone mineralisation. The primary defect is in the mineralisation of normally formed osteoid (organic matrix) at sites of bony turnover. Reduced mineralisation results in soft bones which are easily deformed and fractured. Symptoms, if present, are varied and consequently diagnosis is missed leading to delayed treatment. It is commonly misdiagnosed as hypothyroidism, inflammatory myopathies, multiple myeloma and even arthritis. The most common cause in Ireland is vitamin D deficiency. Diagnosis is made with a combination of clinical, laboratory and radiographic findings. Bone biopsy is the gold standard, but in practice is rarely performed. Treatment most commonly involves calcium and vitamin D supplements.
world's population is not getting an amount of vitamin D sufficient to maintain healthy bone mass and minimize the risk of fracture. The workshop members also agreed that vitamin D insufficiency decreases muscle strength and increases the risk of falls.1 Vitamin D deficiency is one of the most common nutritional deficiencies in Europe. A recent European study has identified 13% of its sample population from across 9 EU countries as having vitamin D deficiency (<30nmol/l).2 A Cork based Irish study completed in 2012 found the average prevalence of vitamin D deficiency to be 6.7%, increasing in winter to 7.5%.3 This is even more profound if we use the cut off of <50nmol/l which the Royal Osteoporosis Society uses to treat patients with additional risk factors4, based on the same Cork based cohort prevalence rises to 40.1% all year round and peaks at 55% in winter.
Introduction Osteomalacia is still an important metabolic bone disease. It is sometimes confused with rickets which is a disorder of defective mineralization of cartilage in the epiphyseal growth plates of children. Osteomalacia and rickets can occur together in children (open growth plates), but only osteomalacia occurs in adults (fused growth plates). Several different disorders cause osteomalacia via mechanisms that result in hypocalcaemia, hypophosphatemia, or direct inhibition of the mineralization process. The most common cause in the general population is vitamin D deficiency. Vitamin D Deficiency At an international workshop on vitamin D held in 2007, there was agreement that most of the
Vitamin D has a well-established role in calcium homeostasis and in maintaining bone health and preventing osteomalacia. Deficiency of this vitamin leads to inadequate skeletal mineralization and leaching of calcium from the skeleton and is the commonest cause of osteomalacia in Ireland.5 This can occur through many mechanisms. Deficiency can be a result of increased requirements such as during adolescence,
pregnancy and lactation. Decreased synthesis of vitamin D can also lead to deficiency. This can be caused by reduced sunlight exposure at higher latitudes as 90% is synthesised in the skin and only 10% found in diet. During winter periods we are particularly vulnerable as sun exposure in Ireland is only strong enough to provide synthesis from June – September. At risk also are indoor workers and those with increased skin pigmentation, as well as those who cover up for cultural or religious reasons. Another cause is inadequate absorption of vitamin D which can be due to gastrointestinal diseases including coeliac disease or inflammatory bowel disease. Impaired metabolism of vitamin D can also lead to deficiency. Hepatic failure limiting 25-hydroxylation of vitamin D or chronic renal disease resulting in inadequate 1α hydroxylation can be implicated. There are many less common causes of osteomalacia including hypophosphatemia, renal tubular acidosis and exposure to drugs that inhibit the mineralisation process such as fluoride, aluminium and possibly nitrogen containing bisphosphonates.6 Clinical Features
study with diagnosis made on clinical, laboratory and radiological grounds.8 Fractures can occur with little or no trauma and typically involve the ribs, vertebrae and long bones. Difficulty walking and waddling gait may also be a feature. It is likely that high levels of parathyroid hormone (PTH) and low levels of phosphate and calcitriol all contribute to the myopathy and similar findings occur in severe primary hyperparathyroidism. Muscle spasms, muscle cramps, a positive Chvostek's sign and tingling or numbness. Abnormal spinal curvature or deformity of the thorax or pelvis appears only in severe osteomalacia of long duration.9 As a result of its varied presentation it can often be misdiagnosed as hypothyroidism, inflammatory myopathy, multiple myeloma or even arthritis. Laboratory Features Laboratory features of osteomalacia secondary to vitamin D deficiency have been identified in retrospective reviews10 and include: • Alkaline phosphatase elevated in 95 to 100%
• Serum calcium and phosphorus The features of osteomalacia, reduced in 27 to 38% if present, are often insidious in onset. Bone pain and muscle • Urinary calcium low in 87% weakness are the most common • 25-hydroxyvitamin D (25[OH]D, symptoms and are present in over calcidiol) <15 ng/mL in 100% 90% of patients with bone biopsy proven osteomalacia.7 Pain is • PTH elevated in 100% generally dull and exacerbated It is worthwhile to note the by weight bearing. Proximal majority of these patients muscle weakness is often a had nutritional osteomalacia marked feature. Patients may from either a gastrointestinal have difficulty climbing stairs disorder or suboptimal nutrition or getting out of a chair. Bony and inadequate sun exposure. tenderness occurred in 88% They have laboratory features of patients in one study with 7 consistent with may secondary biopsy proven osteomalacia and proximal medial femur. True fractures occur through the and 100% of patients in another hyperparathyroidism.
Image 1: Osteopenia changes involving bony pelvis and proximal femurs. Multiple pseudofractures are seen involving the superior and inferior pubic rami bilaterally. There is also a transcervical fracture on the right side. Image from Radiopedia.org
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Image 1: Osteopenia changes involving bony pelvis and proximal femurs. Multip superior and inferior pubic rami bilaterally. There is also a transcervical fracture