Valor clínico del puntaje óseo trabecular calculado a partir de la absorciometría de rayos X de energía dual de columna / Clinical importance of the Trabecular Bone Score obtained from spine dual-energy x-ray absorptiometry

Intrínsecamente, se acepta el hecho de que definir a la osteoporosis solamente sobre la base de la densidad mineral ósea proyectada (DMO mediante DXA) ha llegado a su límite. De hecho, el aspecto multifactorial de esta enfermedad hace que la definición actual de osteoporosis evolucione hacia un modelo de riesgo complejo basado en el Factor de Riesgo Clínico (FRC) y la DMO. El puntaje óseo trabecular (TBS, Trabecular Bone Score) es una nueva medición de escala de grises que se basa en el uso de variogramas experimentales sobre imágenes en proyección 2D, y que permite diferenciar entre dos microarquitecturas tridimensionales (3D) que presentan la misma densidad ósea pero diferentes características trabeculares. El TBS mide la tasa promedio de variación local en escala de grises sobre imágenes de proyección 2D. Este parámetro se obtiene luego del re-análisis de un examen de DXA, y puede compararse con la DMO dado que ambos evalúan la misma región ósea. El valor agregado del TBS respecto de la densitometría mineral ósea para la evaluación del riesgo de fracturas ha sido documentado en estudios transversales, prospectivos y longitudinales. De hecho, se ha hallado que el TBS: 1) es más bajo en mujeres posmenopáusicas con una fractura osteoporótica previa, comparado con mujeres sin fractura pareadas por edad y DMO; 2) brinda un aumento incremental en el odds ratio para fractura de columna cuando se combina con la DMO de columna; 3) es más bajo en mujeres con fracturas (comparado con aquellas sin fracturas), independientemente de si su DMO reúne los criterios para osteoporosis u osteopenia; 4) predice fracturas en forma prospectiva, tal como lo hace la DMO; 5) rescata alrededor de 1/3 de las fracturas clasificadas de manera errónea según la definición de DMO de la OMS para osteoporosis aislada; y 6) se comporta de manera diferente de acuerdo con el tipo de terapia ósea implementada. El objetivo de esta breve revisión consiste en brindar información acerca de los ensayos clínicos actuales referentes al TBS, además de posicionar a este parámetro en la práctica clínica como complemento de la DMO en vista de su actual validación.

Intrinsically it is accepted that defining osteoporosis on the sole basis of projected bone mineral density (BMD by DXA) has reached its limit. Indeed, the multifactorial aspect of this disease means that the current definition of osteoporosis is evolving towards a complex risk model based on Clinical Risk Factor (CRF) and BMD. The Trabecular Bone Score (TBS) is a novel grey-level texture measurement that is based on the use of experimental variograms of 2D projection images, and is able to differentiate between two 3-dimensional (3D) micro-architectures that exhibit the same bone density, but different trabecular characteristics. TBS measures the mean rate of local variation of grey levels in 2D projection images. The TBS is obtained after re-analysis of a DXA exam, and can be compared with BMD, since both evaluate the same region of bone. The added value of the TBS in bone mineral densitometry for fracture risk assessment has been documented in cross-sectional, prospective and longitudinal studies. Indeed, TBS has been found to: 1) be lower in post-menopausal women with a past osteoporotic fracture compared with age- and BMD-matched women without fracture; 2) give an incremental increase in the odds ratio for spine fracture when combined with spine BMD; 3) be lower in women with (versus without) fractures, irrespective of whether their BMD met the criteria for osteoporosis or osteopenia; 4) prospectively predict facture as well as spine BMD; 5) recapture around 1/3 of mis-classified fractures according to the BMD WHO definition of osteoporosis alone, and 6) react differently according to the type of bone therapy. The aim of this short review is to report the current clinical studies as well as to position TBS in clinical routine to complement BMD in the light of its current validation.

Prevalence of silent vertebral fractures detected by vertebral fracture assessment in young Portuguese men with hyperthyroidism.

BACKGROUND: Hyperthyroidism is a risk factor for reduced bone mineral density (BMD) and osteoporotic fractures. Vertebral fracture assessment (VFA) by dual-energy X-ray absorptiometry (DXA) is a radiological method of visualization of the spine, which enables patient comfort and reduced radiation exposure. OBJECTIVES: This study was carried out to evaluate BMD and the prevalence of silent vertebral fractures in young men with hyperthyroidism. DESIGN: We conducted a cross-sectional study in a group of Portuguese men aged up to 50 years and matched in hyperthyroidism (n=24) and control (n=24) groups. MATERIALS AND METHODS: A group of 48 Portuguese men aged up to 50 years was divided and matched in hyperthyroidism (n=24) and control (n=24) groups. BMD (g/cm(2)) at L1-L4, hip, radius 33%, and whole body as well as the total body masses (kg) were studied by DXA. VFA was used to detect fractures and those were classified by Genant's semiquantitative method. No patient had previously been treated for hyperthyroidism, osteoporosis, or low bone mass. Adequate statistical tests were used. RESULTS: The mean age, height, and total fat mass were similar in both groups (P≥0.05). The total lean body mass and the mean BMD at lumbar spine, hip, and whole body were significantly decreased in the hyperthyroidism group. In this group, there was also a trend for an increased prevalence of reduced BMD/osteoporosis and osteoporotic vertebral fractures. CONCLUSIONS: The results obtained using VFA technology (confirmed by X-ray) suggest that the BMD changes in young men with nontreated hyperthyroidism may lead to the development of osteoporosis and vertebral fractures. This supports the pertinence of using VFA in the routine of osteoporosis assessment to detect silent fractures precociously and consider early treatment.