Letter to the Editor: Comments on “Are biochemical markers of bone turnover representative of bone histomorphometry in 370 postmenopausal women?” by Chavassieux P, Portero-Muzy N, Roux JP, Garnero P, Chapurlat R.

We read with interest the paper by Chavassieux et al (1), reporting about the partial discrepancy between histomorphometric parameters assessed on biopsies of the iliac crest and biochemical markers of bone turnover. Despite the highly significant correlations found, the respective low coefficients indicated relatively modest associations. In fact, as correctly stated by the authors, bone markers concentration results from the turnover rate of the skeleton as a whole, whereas histomorphometric indexes reflect its activation at a definite site. This has to be considered particularly relevant in the current study, which investigated women with a wide age range. Using a modified scintigraphic technique in a group of 84 women aged 22–86 years, in the same subjects, we assessed both the global skeletal uptake of ^99mTc-methylene diphpsphonate and the focal uptake of the tracer at well defined, very small (7 × 7 pixels each) skeletal sites (ie, lumbar spine, femoral neck, femoral shaft, and iliac wing, at a site very close to that of usual bone biopsy sampling) (2). We showed that the tracer spot uptake progressively increased with age at the femoral diaphysis (almost entirely made of cortical tissue), whereas it significantly decreased with age in the sites with higher trabecular content, including the iliac wing. So we believe that in a sample comparable with that studied by Chavassieux et al, a similar age-related redistribution of bone turnover rate could well take place. Such a phenomenon could be ascribed to the progressive postmenopausal decrease of trabecular number and to the concomitant cortical bone trabecularization. This in turn decreases the surface amenable for turnover in trabecular tissue, whereas it increases it at the cortical level. The high prevalence of vitamin D insufficiency/deficiency and the consequent increased prevalence of secondary hyperparathyroidism (3) could contribute to cortical involvement (4), as suggested by the correlation found in the current study between serum C-terminal telopeptide and PTH levels.

We believe that the hypothesized age-related redistribution of bone turnover activation rates of different skeletal sites, even if it cannot abolish, may weaken the correlation between histomorphometric parameters obtained from the iliac bone and the integrated mean of the overall skeletal turnover represented by serum biomarkers concentration, in each sample encompassing subjects with a wide range of age. We hypothesize that more tight associations and higher correlation coefficients could have been obtained by studying a sample of women with a narrow age range.

Disclosure Summary: The authors have nothing to disclose.

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