RESUMEN
OBJECTIVE: To determine whether real-time ultrasound imaging can provide quantitative data that distinguish pathologic from healthy muscle and that correlate with strength measures. DESIGN: Nonrandomized matched-pair, repeated-measures design. SETTING: Ultrasound imaging laboratory, rehabilitation medicine department, government research hospital. PARTICIPANTS: Nine patients with stable active or inactive myositis, stratified into 3 groups based on their 10-point manual muscle test (MMT) scores, and 9 age- and gender-matched controls. INTERVENTIONS: Maximal isometric contraction of the rectus femoris muscle in 2 knee-flexion positions (60 degrees, 90 degrees ) during simultaneous ultrasound imaging and muscle force dynamometry. MAIN OUTCOME MEASURES: Changes of the rectus femoris muscle in horizontal (X) and vertical (Y) diameters between relaxed and contracted states, and muscle force measurements. RESULTS: The X diameters decreased and the Y diameters increased during isometric contraction in all participants. For each group, average changes in cross-sectional diameters were consistently higher in controls than in patients. Patients with MMT less than 8 differed significantly from controls in both X and Y dimensions. A moderately strong correlation was found between muscle force and the Y diameter during contraction at 60 degrees (r =.78) and 90 degrees (r =.67) knee-flexion angles. CONCLUSIONS: Ultrasonography provided a quantitative measure of change between relaxed and contracted state of muscle, which correlated with muscle force. Ultrasound identified significant differences in cross-sectional diameters between the myopathic and normal muscles sampled and may be useful for measuring muscle response to drug and exercise therapy.