Discrepancy between bone density and bone material strength index in three siblings with Camurati-Engelmann disease.

Camurati-Engelmann (CE) is a very rare disease affecting one in every million persons worldwide. It is characterized by an enlargement of long bones. We aimed to assess bone characteristics in three siblings with different tools. Even if there was an excess of bone density, quality seemed to be deteriorated.
Introduction: CE disease is a rare monogenic disorder affecting approximately one in every million persons worldwide. It is mainly characterized by a progressive hyperostosis of the periosteum and endosteum of the diaphysis of long bones. Limited data are available about bone characteristics in these patients. In three siblings with CE disease, we aimed to assess bone mineral density (BMD) and trabecular bone score (TBS) by dual-energy X-ray absorptiometry (DXA) and material characteristics at tissue level using bone impact reference point indentation.
Methods: Clinical data were collected and a general laboratory workup was performed. At the lumbar spine and hip, BMD and TBS were measured using DXA imaging. Bone material strength index (BMSi) was measured by bone impact microindentation using an Osteoprobe instrument.
Results: All three cases had densitometric values consistent with high bone mass (sum of Z-score at the lumbar spine and hip > 4). Hip BMD was extremely high in all three siblings at both total hip and femoral neck, while at the lumbar spine, two of them had normal values but the third again had very high BMD. TBS values were in the normal range. In contrast, BMSi measurements were at low or very low levels, compared with normal controls.
Conclusion: Despite strikingly increased BMD and normal microarchitecture, BMSi is affected in patients with CE. Microindentation could be an appropriate tool for assessing bone fragility in these patients. Bone disease in this group of patients requires further study to better understand the underlying regulatory mechanisms and their alterations.