Assessing spinal muscular atrophy with quantitative ultrasound.
OBJECTIVE
To assess the value of quantitative ultrasound in patients with type 2 and 3 spinal muscular atrophy (SMA).


METHODS
Twenty-five patients with SMA (15 type 2 and 10 type 3) and 21 normal subjects were enrolled for this observational study. Strength of biceps brachii, wrist extensors, quadriceps, and tibialis anterior were measured with hand-held dynamometry. In addition, these 4 muscles were studied with a standard ultrasound system using a 5-MHz probe, and luminosity values for each muscle and the overlying subcutaneous fat were obtained by subsequent image analysis. A luminosity ratio (LR) for each muscle was calculated by dividing the muscle by the subcutaneous fat luminosity. The LR and strength scores for all 4 muscles were averaged to provide a single summary value for each patient.


RESULTS
The LRs increased with disease severity: 1.27 +/- 0.26 for normal subjects, 2.43 +/- 0.78 for type 3 SMA, and 3.85 +/- 1.3 for type 2 SMA (p < 0.001). Taking all the normal subject and patient data together, there was a good correlation between strength and LR (r = -0.711, p < 0.001). There was also a moderate relationship between LR and strength in the patients with SMA alone (r = -0.588, p = 0.008), and, as expected, a nonsignificant relationship between LR and strength in normal subjects (r = -0.011).


CONCLUSIONS
Quantitative ultrasound has the potential of serving as a marker of SMA severity and may be useful in future clinical trials.
Wu
Jim S
JS
Department of Radiology, Beth Israel Deaconess Medical Center, Boston, MA, USA.
Darras
Basil T
BT
Rutkove
Seward B
SB
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D007223:Infant; D008297:Male; D053580:Muscle Strength / Q000502:physiology; D009134:Muscular Atrophy, Spinal / Q000145:classification / Q000000981:diagnostic imaging / Q000503:physiopathology; D014897:Spinal Muscular Atrophies of Childhood / Q000145:classification* / Q000000981:diagnostic imaging* / Q000503:physiopathology; D014463:Ultrasonography; D055815:Young Adult