Bone Abstracts

In children with spinal muscular atrophy (SMA): i) describe bone mineral density (BMD) measured by dual-energy x-ray absorptiometry (DXA); ii) examine bone health factors; iii) examine change in BMD over time and pamidronate effect.

DXA results, medications, ambulation, 25-OH-Vit D levels, and fracture history were retrospectively reviewed in 14 children (five girls) with SMA. Sites scanned included whole body (WB), lumbar spine (LS), and lateral distal femur (LDF). Age and gender-matched z-scores were calculated.

There were nine type I, four type II and one type III SMA patients with a mean age of 9.9 years (range 3.1–18.5) at the initial DXA scan. Five subjects had serial DXA studies, including two treated with pamidronate. Thirteen patients were non-ambulatory; the type III patient used a walker.

LDF DXA was obtained on all subjects. Mean (range) LDF BMD z-scores were: R1 −9.0 (−3.1 to −18.5); R2: −6.6 (−3.8 to −14.3) R3: −5.6 (−2.7 to −12.6). Only six LS and four WB measurements could be obtained due to scan artifacts. Average LS (−2.2 (0.8 to −2.7)) and WB (−2.5 (−1.2 to −3.8)) BMD z-scores were higher than LDF scores. The type III patient had normal LS and WB BMD but low LDF values. Five patients had history of fracture (three non-traumatic, two with multiple fractures received pamidronate). Available 25-OH-Vit D levels at the time of initial DXA (n=4) ranged from 23 to 40.1 ng/dl, with median level of 30.5.

Serial scans: Length of observation ranged from 2 to 4 years in two treated patients and from 0.7 to 3.7 years in three untreated patients. Both treated patients had SMA type I and fractured young (ages 1 and 3 years). As expected, their z-scores increased dramatically with pamidronate. BMD remained low over time in the untreated patients.

Children with SMA have below normal BMD, particularly of the lower extremities. Two patients who suffered multiple non-traumatic fractures and received bisphosphonate saw improved BMD and have not fractured since treatment began. The LDF proved to be the most accessible DXA site to measure in children with SMA.

Disclosure: The authors declared no competing interests.