Bone Abstracts

Objective: To examine the bone mineral density (BMD), fracture occurrence and history in a cross-section of subjects with Pelizaeus Merzbacher Disease (PMD).

To describe the effect of pamidronate therapy on BMD over time in treated PMD patients.

Methods: We examined the medical history, medications, level of ambulation, fracture history and DXA results in 15 boys with PMD. Body sites scanned included whole body (WB) when possible, lumbar spine (LS), and lateral distal femur (LDF). Age and gender-matched z-scores were calculated using manufacturer-provided normative values for LS and WB, and published norms for the LDF.

Results: 15 males with a mean age of 14.2 years (range 1.1–33.2) at the time of initial DXA were included in this study. All were non-ambulatory. Three subjects reported non-traumatic fracture. This subgroup received bisphosphonate according to a serial cyclic protocol. Standard pediatric DXA sites were problematic; WB measure was only able to be obtained on eight subjects. LS was obtained on nine subjects and six subjects had spinal fusion rods. We were able to obtain LDF DXAs on every subject. BMD z-scores were not available for the two youngest subjects.

BMD was low at all sites measured in all subjects. Mean (and range) total body less head BMD z-score was −3.7 (−2.7 to −6.2). Mean LS BMD z-score was −4.1 (−2.0 to −6.5); for the LDF: R1 −4.6 (−2.6 to −7.4); R2: −8.9 (−2.7 to −25.1); R3: −4.6 (−2.1 to −7.9).

The three subjects treated with pamidronate had no adverse effects to the cyclic protocol. Two had serial DXA scans with 2 and 3.5 years of observation. BMD improved and z-scores improved in all LDF regions with treatment and no additional fractures occurred.

Conclusions: Boys with PMD have low BMD at all body sites tested, particularly in the lower extremities. In a subgroup with non-traumatic fractures, LDF BMD improved with bisphosphonate and no additional fractures have occurred. As demonstrated in other populations with physical disabilities, the LDF proved to be an easily-obtained, useful alternative DXA site.

Disclosure: The authors declared no competing interests.