Muscular dystrophy patients show low exercise-induced blood flow in muscles with normal strength

Abstract

Objective: Neuromuscular evaluation increasingly employs muscle ultrasonography to determine muscle thickness, mean grayscale echointensity, and visual semiquantitative echotexture attenuation. However, these measures provide low sensitivity for detection of mild muscle abnormality. Exercise-induced intramuscular blood flow is a physiologic phenomenon, which may be impaired in mildly affected muscles, particularly in dystrophinopathies, and may indicate functional muscle ischemia. We aimed to determine if muscle blood flow is reduced in patients with neuromuscular disorders and preserved muscle strength, and if it correlates with echointensity and digital echotexture measurements.

Methods: Peak exercise-induced blood flow, echointensity, and echotexture were quantified in the elbow flexor muscles of 15 adult patients with Becker muscular dystrophy (BMD) and 13 patients with other muscular dystrophies (OMD). These were compared to 17 patients with Charcot-Marie-Tooth type 1 (CMT1) neuropathy and 21 healthy adults from a previous study.

Results: Muscle blood flow was reduced in all patient groups compared to controls, most prominently in BMD patients (p < 0.0001). Echointensity was similarly increased in all patient groups (p < 0.05), while echotexture was reduced only in muscular dystrophy patients (p ≤ 0.002). In BMD, blood flow correlated with echotexture (Pearson r = 0.6098, p = 0.0158) and strength (Spearman r = 0.5471; p = 0.0370). In patients with normal muscle strength, reduced muscle blood flow was evident in all patient groups (p < 0.001), echotexture was reduced in BMD and OMD (p < 0.01), and echointensity was increased in CMT (p < 0.05).

Interpretation: Muscle blood flow is a sensitive measure to detect abnormality, even in muscles with normal strength. Increased echointensity may indicate a neurogenic disorder when strength is preserved, while low echotexture suggests a dystrophic disease.

Figure 1

Power Doppler and ultrasound imaging of the elbow flexor muscles. A healthy control muscle (A) shows prominent blood flow, while this is reduced in a BMD patient (B), and in a patient with a dysferlinopathy (C). The echotexture of a normal muscle is heterogeneously speckled (D), attenuated in muscular dystrophy patients (E and F). Histogram analysis of the corresponding above‐placed photos shows the echotexture distribution pattern, the mean echointensity value, and the standard deviation. In contrast with the healthy control (G), both BMD (H) and dysferlinopathy (I) patients show increased mean and reduced standard deviation of echointensity. The X axis of the histograms represents echointensity values between 0 and 255, and the Y axis represents the frequency of observations. BMD, Becker muscular dystrophy; SD, standard deviation.

Figure 2

Exercise‐induced intramuscular blood flow, muscle echointensity, and echotexture heterogeneity quantification. Blood flow as % blood in an area of muscle (A), mean echointensity (B), and echotexture as the standard deviation of echointensity histogram analysis (C) are shown. ANOVA Tukey's multiple comparisons ****p < 0.0001; ***p = 0.0001; **p < 0.01; * p < 0.05. BMD, Becker muscular dystrophy; CMT, Charcot–Marie–Tooth; OMD, other muscular dystrophy; SD, standard deviation.

Figure 3

Correlation of intramuscular blood flow with echotexture and muscle strength. In BMD patients blood flow correlated with (A) echotexture heterogeneity (Pearson r = 0.6098, p = 0.0158, two‐tailed analysis) and with (B) muscle strength (Spearman r = 0.5471; p = 0.0370, two‐tailed analysis). Blood flow in controls and patients with normal muscle strength (C). ****p < 0.0001; ***p = 0.0007; **p < 0.01; *p < 0.05. BMD, Becker muscular dystrophy; CMT, Charcot–Marie–Tooth; OMD, other muscular dystrophy; SD, standard deviation.

Figure 4

Receiver operator characteristics. Blood flow (% blood area) evaluation showed a higher area under the curve (AUC) for detecting an abnormality in comparison to echointensity and echotexture (echointensity SD) analysis in our entire mixed patient population with normal strength (A), muscular dystrophy patients with normal elbow flexion strength (B), BMD patients with normal strength (C), and patients with OMD with normal strength (D). BMD, Becker muscular dystrophy; OMD, other muscular dystrophy; SD, standard deviation.