Greining á beinþynningu meðal aldraðra : yfirlitsgrein

Abstract

Measurement of bone mineral density (BMD) is the basis of the diagnosis of osteoporosis. WHO classification of osteoporosis is based on dual energy X-ray absorptiometry (DEXA) using the BMD of young women (20-30 years) as the reference value (T-score). For clinical purpose it is better to use age-matched control (Z-score) to evaluate future fracture risk in relation to other individuals of the same age. A further facility of the new bone densitometry technique is the option of vertebral morphometry, which makes it possible to assess previous vertebral fractures with similar precision as conventional X-ray. Such an assessment is of the greatest importance as patients with previous fractures and low BMD have several fold increased risk of further fractures and benefit most from medical therapy. There are errors of accuracy in all bone densitometry techniques and also in the interpretation of the data. Osteoarthritis in the lumbar spine, common in the elderly, creates false increment in BMD as measured by DEXA. For this reason the hip is the site of choice for BMD measurement in the elderly, especially as it predicts best femoral fractures, a major concern in the elderly. Quantitative computed tomography has the advantage of measuring separately cancellous and cortical bone. Ultrasound of bone (at present mostly in calcaneus) may provide new measures of bone fragility. Ultrasound has the advantage of no exposure to radiation and the equipment is portable. Although useful bone ultrasound cannot replace bone densitometry in the diagnosis and monitoring of therapy. Biochemical bone markers are not useful in the diagnosis of osteoporosis, but they can be useful in deciding on intervention and in monitoring the efficacy of treatment. Biochemistry is videly used in the differential diagnosis of secondary osteoporosis. History and physical examination are insufficient in diagnosing osteoporosis, but they are of utmost importance in finding individuals of high risk who might benefit most from undergoing bone densitometry. History and physical examination are also important in targeting other investigations to exclude secondary forms of osteoporosis. Although bone densitometry is usually necessary for the diagnosis of osteoporosis intervention by drugs should be based in addition on general assessment of the patient taking notice of other important independent risk factors for fractures.

Greining á beinþynningu byggist á mælingu á beinþéttni. Skilgreining Alþjóðaheilbrigðisstofnunarinnar á beinþynningu byggir á mælingu beinþéttni með röntgengeisla (tvíorkudofnunarmæling, dual energy X-ray absorptiometry, DEXA) þar sem viðmiðunin er meðalgildi 20-30 ára kvenna (T-gildi). Í klínískum tilgangi er eðlilegra að styðjast við aldursbundinn samanburð (Z-gildi) og meta brotaáhættuna miðað við einstaklinga í sama aldurshópi. Nýleg beinþéttnimælitæki gefa auk þess möguleika á að framkvæma formmælingu á hryggjarliðbolum (morphometria) sem gefur kost á að meta fyrri samföll af svipaðri nákvæmni og venjuleg röntgenmynd. Slíkt mat hefur mikið gildi þar sem einstaklingur með sögu um fyrri brot og lága beinþéttni hefur margfalda áhættu á frekari brotum og þessir einstaklingar svara jafnframt best meðferð.