Longitudinal changes in ultrasound measurements: a parallel study in subjects with genetic disorders and healthy controls

Disturbances in skeletal status in subjects with genetic disorder may increase their fracture risk. The aim of the study was longitudinal observation of phalangeal speed of sound changes across the bone over a period of 2 y in 24 patients (14 boys and 10 girls, mean age 9.63 +/- 1.8 y.) and 24 age-matched healthy controls (14 boys and 10 girls, mean age 9.65 +/- 1.71 y.). Weight and height did not differ between patients and controls at baseline and follow-up. Patients with the following disorders were evaluated: 7 with Down syndrome, 6 nonspecific mental retardations of unknown etiology, 5 Martin-Bell syndrome and 6 with other diseases. In patients and controls, no factors potentially influencing bone metabolism (except for genetic disorder) were present. Bone status was assessed by quantitative ultrasound at hand phalanges using DBM Sonic 1200 (IGEA, Carpi, Italy), which measures amplitude-dependent speed of sound (Ad-SoS [m/s]). At baseline, Ad-SoS and Z-score were significantly lower in patients than in controls (1892 +/- 51 m/s versus 1936 +/- 43 m/s, p < 0.01 and -1.47 +/- 1.43 versus -0.14 +/- 1.04, p < 0.001, respectively. In follow-up, Ad-SoS and Z-score increased significantly in patients (1892 +/- 51 m/s to 1934 +/- 48 m/s, p < 0.0001 and -1.47 +/- 1.43 to -0.76 +/- 1.00, p < 0.01, respectively) and in controls (1936 +/- 43 m/s to 1976 +/- 60 m/s and -0.14 +/- 1.04 to 0.31 +/- 1.08, p < 0.05, respectively). Follow-up Ad-SoS and Z-Score were significantly lower in patients (p < 0.01). Longitudinal changes in Ad-SoS, Z-score weight did not differ between patients and control, and height increased more in controls (13.2 +/- 2.8 cm versus 11.4 +/- 5.9 cm, p < 0.05)+). In patients, Ad-SoS increased by 42 m/s (2.22%), and in controls increased by 40 m/s (2.07%). Difference in Ad-SoS between patients and controls was 44 m/s at baseline and 42 m/s at follow-up. Using the value of the least significant change (LSC = 20.5 m/s), in 16 patients (67%) and in 18 controls (75%) Ad-SoS showed an increase greater than the LSC, in one control (4%) a decrease greater than the LSC and in rest of subjects studied remained unchanged (33% patients and 19% controls) over a period of observation. In conclusion, despite comparable improvement in measured ultrasound parameter in patients and controls observed over a study duration, the difference between them remained stable.