Prevalence and causes of elevated bone mass

Reports of elevated bone mass (EBM) on routine DXA scanning are not infrequent. However, epidemiological studies of EBM are few in number and definition thresholds variable. The purpose of this study was to assess the prevalence and causes of EBM in the general population referred to a single university hospital – catering for a population of 4 million inhabitants – for DXA scanning. DXA databases were initially searched for individuals with a bone mineral density (BMD) Z-score ≥+4 at any site in the lumbar spine or hip from April 1st, 2008 to April 30st, 2018. Two Hologic scanners were available at the Lille University Hospital (France). Prevalence of EBM was evaluated, as were causes associated with EBM. At the lumbar spine, 18,229 bone density tests were performed in women and 10,209 in men. At the hip, 17,390 tests were performed in women and 9857 in men. The total number of patients who had at least one bone density test was 14,745, of which 64.2% were female. Of these 14,745 patients, 211 had a Z-score ≥+4 at any site, i.e. a prevalence of 1.43% [1.25%–1.64%]. The DXA scans and medical records of 92 men and 119 women with elevated BMD were reviewed to assess causes. An artefactual cause was found in 164 patients (75%) with EBM (mostly degenerative disease of the spine), and an acquired cause of focal EBM was found in only 2 patients, both of whom had sclerotic bone metastases from prostate cancer. An acquired cause of generalized EBM was found in 32 patients (15%), the vast majority of whom had renal osteodystrophy (n = 11), followed by hematological disorders (n = 9; e.g. myeloproliferative syndromes and mastocytosis) and diffuse bone metastases from solid cancer (n = 5). Of the remaining causes, rare hereditary diseases (e.g. osteopetrosis…) and unexplained EBM were found in 10 and 6 cases respectively. The prevalence of EBM (Z-score ≥+4 at any site) was 1.43% [1.25%–1.64%]. In nearly all instances (97.1%) the explanation for EBM could be found in the medical record and through conventional investigations. This study suggests that the main cause of EBM is degenerative disease of the spine. Further studies are needed to differentiate artefactual EBM from hereditary or acquired EBM, and to investigate unexplained EBM. Genetic testing may prove useful in elucidating rare unknown causes.