Myofascial trigger points (MTrPs) treatments using compression or known as “ischemic compression,” has been reported to provide immediate relief of musculoskeletal pain and reduce the sympathetic activity that exacerbates chronic pain. A pilot study from Japan investigated the possible involvement of the prefrontal cortex in pain relief from MTrP compression.
The study recruited 21 female subjects with chronic neck pain, they were randomly assigned to two groups: MTrP compression (n = 11) or Non-MTrP compression (n = 10). Ischemic compression consisted of constant deep pressure by the thumb, which was applied to MTrPs or Non-MTrPs in the trapezius muscle. The identification of MTrPs requiring (1) the presence of a hypersensitive tender point in a taut band in the muscle, (2) recognition by the patient of the pain as “familiar” when compression is applied to the point, and (3) induction of pain when the muscle including the MTrP is stretched. The Non-MTrPs were defined as points 2 cm away and proximal to a given MTrP, where a taut band was not detected and local and referred pain was not induced when compression was applied to the point. Compression for 30 s was conducted 4 times.
During the experiment, prefrontal hemodynamic activity [changes in Oxy-hemoglobin (Hb), Deoxy-Hb, and Total-Hb concentrations] was measured using near infrared spectroscopy (NIRS). In addition, autonomic activity based on heart rate variability (HRV) was monitored using electrocardiography (ECG).
The results indicated that MTrP compression significantly reduced subjective pain compared with control. The HRV data indicated that a low frequency (LF) component of HRV was decreased, and a high frequency (HF) component of HRV was increased during MTrP compression. Prefrontal hemodynamic activity was significantly decreased during MTrP compression compared with control. Furthermore, changes in autonomic activity were significantly correlated with changes in subjective pain and prefrontal hemodynamic activity.
The authors concluded that MTrP compression in the neck region alters the activity of the autonomic nervous system via the prefrontal cortex which in turns reduce subjective pain.