A new application of ultrasound imaging to characterize tissue properties and blood flow in myofascial pain syndromes

Abstract

Myofascial pain syndrome (MPS) is a common, yet poorly understood, acute and chronic pain condition. MPS is characterized by local and referred pain associated with hyperirritable nodules known as myofascial trigger points (MTrPs) that are stiff, localized spots of exquisite tenderness in a palpable taut band of skeletal muscle. Our objective was to evaluate ultrasonic methods for imaging MTrPs and surrounding soft tissue. We recruited 16 subjects with acute neck pain. Based on physical examination, four sites in each patient were labeled as active MTrP (spontaneously-painful), latent MTrP (non-painful), or palpably normal. At these sites, we performed conventional B-mode and Doppler imaging; and vibration sonoelastography (VSE) by inducing vibrations (∼100Hz) with a handheld vibrator. Raw RF data were acquired for offline processing. Qualitatively, three observers scored the B-mode and VSE images on a 5-point scale based on the presence and number of nodules, and the Doppler velocity spectra on a 5-point scale based on waveform morphology. Quantitatively, we estimated the spectral parameters, midband fit, zero-frequency intercept and slope, from calibrated RF spectra, and Doppler waveform parameters from spectral envelope tracings. MTrPs appeared as focal, hypoechoic nodules, and as focal regions of reduced vibration amplitude on VSE. Sites with MTrPs on physical exam were more likely to have one or more hypoechoic and/or stiffer nodules on imaging compared to normal muscle (p<0.05). Arteries near MTrPs had different flow waveform morphology with retrograde diastolic flow (p<0.02). Based on quantitative measures, MTrPs were distinct from normal muscle and active MTrPs could be differentiated from latent ones (p<0.04). With further refinement, these methods could lead to objective diagnostic criteria and clinical outcome measures for MTrPs.