M.Sc Thesis

M.Sc StudentBar-Bachar Ofrit
SubjectIntramuscular Stimulation for Myofascial Pain and its
Effects on Peripheral and Central pain Modulation
DepartmentDepartment of Medicine
Supervisors PROF. Elon Eisnberg
PROF. David Yarnitsky
Full Thesis textFull thesis text - English Version


Impaired Conditioned Pain Modulation (CPM) and/or enhanced Temporal Summation has been found in several chronic pain disorders, among them migraine, fibromyalgia and osteoarthritis. Little is known on pain modulation of chronic myofascial pain syndrome (MPS). MPS is characterized by autonomic, sensory and motor symptoms caused by myofascial trigger points (TrPs).  We aimed to assess the pain measures and pain modulation of chronic MPS patients and to examine how intramuscular stimulation (IMS) affects their segmental and central pain measures. We hypothesized that patients with chronic MPS would show a reduced CPM effect and/or an enhanced TS effect. We also hypothesized that IMS will cause pain reduction and accordingly, will normalize these measures. Fifty-six chronic unilateral MPS patients and thirty controls were recruited for our trial. All subjects were examined by a pain physician. Patients were randomly allocated to either the IMS (n=26) or sham (n=30) treatment. Subjects underwent psychophysical testing before and after treatment. Controls waited at the physician's office during treatment time. The psychophysical assessor was blinded to the subjects' condition and treatment. Psychophysical evaluation consisted of: dynamic mechanical allodynia (DMA)-brush stroke, supra-threshold mechanical pain (STMP)-von Frey, mechanical temporal summation (MTS)-von Frey, heat temporal summation (TS)-tonic contact heat stimulation, conditioned pain modulation (CPM)-test pain: phasic contact heat stimuli stand-alone and parallel to conditioning pain by cold pressor hand immersion. The key-TrP (the TrP identified as causing the typical pain pattern of each patient) was marked and served as a reference for TrP marking on controls. Stimuli were applied within the segment contralateral to the focal pain and to a remote site on the contralateral shin to assess segmental vs. central mechanisms. IMS treatment consisted of needling all TrPs on the symptomatic side by inserting the needle into the fascia and muscle, while sham-treatment consisted of inserting the same type of needle into the dermis alone, again only to TrPs on the symptomatic side. This was done to avoid any effect of local sensitization due to needling on the contralateral side where the tests were conducted.

Non-parametric tests revealed differences between the patients and controls in pain ratings of STMP pain both on the shin (controls vs. patients: median, 4.5 vs. 10.33 respectively, p=0.0245) and on the shoulder (controls vs. patients: median, 2.667 vs. 9.667 respectively, p=0.007), pointing to central sensitization to mechanical pain. No other differences in other pain measures were found. Although some IMS treated patients did report pain relief, no significant differences were found between the two treatment groups in any of the measures including pain relief. We conclude that MPS patients suffer from central mechanical sensitization, although no changes in pain modulation measures have been found. Treatment by IMS was not more efficient than sham treatment and did not affect pain measures.