Research Review By Dr. Ceara Higgins©

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Date Posted:

March 2020

Study Title:

Widespread Pressure Pain Sensitivity and Referred Pain from Trigger Points in Patients with Upper Thoracic Spine Pain

Authors:

Ortega-Santiago R, Maestre-Lerga M, Fernández-de-las-Peñas C et al.

Author's Affiliations:

Universidad Rey Juan Carlos, Madrid, Spain; Fisioterapia Kinesis Mostoles, Madrid, Spain; Concord Hospital, Concord, New Hampshire; Regis University, Denver, Colorado; Franklin Pierce University, New Hampshire; Universidad Complutense de Madrid, Madrid, Spain; Instituto de Investigacion Sanitaria del Hospital Clinico San Carlos, Madrid, Spain.

Publication Information:

Pain Medicine 2019; 20(7): 1379–1386.

Background Information:

Spine pain is common and leads to considerable disability and lost work time. While the scientific literature has focused on the cervical and lumbar spines, the thoracic spine has received much less attention despite a lifetime pain prevalence in that region ranging from 15.6%-19.5% (2). Thoracic pain is also more prevalent in women (affecting women 2 times more commonly than men) (3). While this puts the rate of thoracic spine pain much lower than the rates of neck and low back pain, thoracic spine pain can certainly lead to similar degrees of pain and disability (1).

While the origin of spinal pain is multifactorial, one plausible etiology of thoracic spine pain symptoms is the presence of myofascial pain associated with the presence of trigger points (MTrPs) – defined as hypersensitive points within taut bands of skeletal muscles that can lead to referred pain and autonomic phenomenon when stimulated (4). Active MTrPs are associated with spontaneous pain, and the local or referred pain either totally or partially reproduces the patients’ symptoms, while latent MTrPs do not produce spontaneous symptoms, and their elicited referral pain does not reproduce patients’ primary or familiar symptoms (4).

An association between hyperexcitability of the central nervous system, expressed as widespread hypersensitivity to pressure pain, and neck and low back pain has been found (5). However, no studies have examined this phenomenon in thoracic spine pain. No studies examining the presence of MTrPs in patients with thoracic spine pain were found.

This study aimed to compare the incidence of MTrPs and widespread pressure pain sensitivity in individuals with upper thoracic spine pain compared to healthy controls. The authors hypothesized that patients with upper thoracic spine pain would have higher numbers of both active and latent MTrPs and higher sensitivity to pressure pain, and that higher intensity of upper thoracic spine pain and number of active MTrPs would be associated with higher widespread sensitivity to pressure pain.

Pertinent Results:

17 individuals with upper thoracic spine pain and 17 comparable healthy controls were included. No significant demographic differences were found between groups. Patients with upper thoracic spine pain showed higher scores on the PSQI, had an average history of 8.8 years of thoracic pain, an average current intensity of upper thoracic spine pain of 5.7 (out of 10), worst pain intensity in the preceding week of 7.2, lowest pain intensity in the preceding week of 1.4, and an average intensity of pain during movement of 5.9. The intensity of upper thoracic spine pain was highly correlated with PSQI scores, so that the higher the current intensity of upper thoracic pain, the worse the sleep quality.

Patients with upper thoracic spine pain had an average of 12.4 ± 2.8 MTrPs, including 5.7 ± 4.0 active MTrPs and 6.7 ± 3.4 latent MTrPs. Pain-free controls had no active MTrPs and an average of 3.3 ± 3.6 latent MTrPs. In the upper thoracic spine pain group, active MTrPs were most prevalent in the rhomboids (75%), anterior scalene (65%), and middle scalene (47%). Finally, the higher the number of active MTrPs, the greater the reported intensity of pain and duration of pain history.

Latent MTrPs were found in both the upper thoracic spine pain group and the pain-free group. There is some evidence that latent MTrPs can sensitize nociceptive and non-nociceptive nerve endings (7) and activate large-diameter myelinated muscle afferents (2). Latent MTrPs have also been associated with altered motor control patterns (8), accelerated muscle fatigability (9) and increased motor activation (10).

Patients with upper thoracic spine pain showed lower widespread PPTs than controls. However, no significant correlation was found between the number of active or latent MTrPs and PPTs. As well, including gender as a covariate did not influence the results.

Clinical Application & Conclusions:

Individuals with upper thoracic spine pain were found to have significantly more active MTrPs in the cervico-thoracic musculature, which suggests that referred pain from MTrPs may have a role in the development (or persistence) of chronic thoracic spine pain. In addition, participants with upper thoracic spine pain showed lower PPTs at T2, the C5-C6 zygapophyseal joints, second metacarpals, and the tibialis anterior, suggesting sensitization mechanisms in thoracic spine pain.

Referred pain from the rhomboids and anterior and middle scalene muscles reproduced individual’s pain symptoms, especially spontaneous pain in the interscapular region – something to keep in mind clinically! This combined with the association between higher numbers of active MTrPs and higher intensity and longer history of symptoms supports the role of active MTrPs in upper thoracic spine pain. Therefore, proper management strategies targeting active and latent MTrPs could help to reduce pain and disability in this clinical population.

Individuals with upper thoracic spine pain were also found to have lower PPTs (pain pressure thresholds) in symptomatic and distant pain-free areas. This suggests a widespread hypersensitivity to pressure pain, a clinical manifestation of central sensitization. Research has shown that active MTrPs can lead to elevated concentrations of several pain-producing substances and chemical mediators which lead to peripheral nociception (4). However, no relationship was found between the number of active MTrPs and widespread pressure pain sensitivity in the upper thoracic spine pain group. This relationship requires further study.

Study Methods:

Subjects with upper thoracic spine pain were recruited from a physical therapy clinic using the following inclusion criteria:
  • Upper thoracic spine pain in the T1-T4 region
  • Pain intensity score of ≥ 3 on the numeric pain rating scale (0-10)
  • Pain duration of at least 1 year
  • Symptoms provoked by thoracic postures, thoracic movement, or palpation of the thoracic muscles
Age- and sex-matched healthy controls with no history of thoracic pain and no current spinal pain were recruited through local announcements to the general public. In both groups, individuals were excluded based on the following criteria:
  • Any history of spinal surgery
  • Cardiovascular, respiratory, or neurological disorders
  • Any rheumatic condition, osteoporosis, cancer, spinal infection, radicular pain, or neuropathy
Demographic data including age, gender, body mass index and nature and duration of symptoms was collected. Patients were then asked to draw their perceived area of pain on a body chart of the posterior thoracic spine, and a medical examination was carried out for inclusion/exclusion criteria. Participants additionally completed an 11-point numeric pain rating scale (NPRS; 0 = no pain, 10 = maximum pain) for current intensity of thoracic pain at rest, the worst and lowest intensity of thoracic pain experienced in the preceding week and the intensity of pain with movement. Participants also completed the Pittsburgh Sleep Quality Index (PSQI) to assess sleep quality over a one-month period. The PSQI includes 19 self-rated questions and 5 questions completed by a bedmate and/or roommate providing a final score from 0-21 points with higher scores indicating worse quality of sleep. A total score of ≥ 8.0 indicates poor sleep quality (6).

An assessor with 10 years of experience, who was blinded to which group the subject was from, examined the upper trapezius, rhomboids, iliocostalis thoracis, levator scapulae, infraspinatus, and anterior and middle scalene muscles bilaterally for the presence of MTrPs. The order in which the muscles were assessed was randomized and a two-minute rest period was given between testing each muscle. Diagnosis of MTrPs was conducted based on the criteria from Simons et al. (4), which included:
  • A palpable taut band in a skeletal muscle
  • The presence of a hypersensitive spot within a taut band
  • The presence of referred pain in response to MTrP compression
  • Local twitch response elicited by snapping palpation of the taut band
MTrPs were considered active if the local and referred pain reproduced any pain symptom perceived by the subject and recognized as a familiar pain experience. MTrPs were considered latent when both the local and referred pain did not reproduce the subjects’ symptoms (4). This was determined by the patients’ response to being asked, “When I pressed each of these muscles, did you feel any pain locally or in other areas (referred pain)? Please tell me whether the pain that you felt in the other area reproduced any symptom the you usually experience.”

Participants were instructed to avoid using any analgesic or muscle relaxants for 24 hours before the examination. Pain pressure thresholds (PPTs), defined as the minimum amount of pressure needed for the sensation of pressure to change to pain were assessed using a mechanical pressure algometer (kg/cm2) over the T2 spinous process, bilaterally over the C5-C6 zygapophyseal joints, second metacarpals, and tibialis anterior muscles. Participants were asked to press a switch to indicate when the sensation changed from pressure to pain. The average of three trials was calculated and a 30-second rest was allowed between each trial. The order of muscle assessment was randomized for each participant.

Study Strengths / Weaknesses:

Strengths:
  • The use of a control group that was well matched demographically improved generalizability of the data.
Weaknesses:
  • Although the Pittsburgh Sleep Quality Index (PSQI) has good internal consistency and test-retest reliability, its validity or utility in a pain population has not been well-studied.
  • All subjects were from a single geographic location and one therapist performed all of the evaluations, which may affect the generalizability of the data.
  • The study had a small sample size – future studies should include more subjects.
  • The study design did not allow for inferences to be made regarding the causal relationship of MTrPs and widespread pressure pain sensitivity in individuals with upper thoracic spine pain.

Additional References:

  1. Heneghan NR, Rushton A. Understanding why the thoracic region is the ‘Cinderella’ region of the spine. Man Ther 2016; 21: 274-276.
  2. Briggs AM, Smith AJ, Straker LM, et al. Thoracic spine pain in the general population: Prevalence, incldence and associated factors in children, adolescents and adults: A systematic review. BMC Musculoskelet Disord 2009; 10:77.
  3. Fouquet N, Bodin J, Descatha A, et al. Prevalence of thoracic spine pain in a surveillance network. Occup Med 2015; 65(2): 122-125.
  4. Simons DG, Travell JG, Simons L. Myofascial Pain and Dysfunction. The Trigger Point Manual, 3rd ed. Philadelphia, PA: Wolters Kluwer; 2019.
  5. Mlekusch S, Schliessbach J, Camara RJ, et al. Do central hypersensitivity and altered pain modulation predict the course of chronic low back and neck pain? Clin J Pain 2013; 29(8): 673-680.
  6. Carpenter JS, Andrykowski MA. Psychometric evaluation of the Pittsburgh Sleep Quality Index. J Psychosom Res 1998; 45(1): 5-13.
  7. Li LT, Ge HY, Yue SW, et al. Nociceptive and non-nociceptive hypersensitivity at latent myofascial trigger points. Clin J Pain 2009; 25(2): 132-137.
  8. Lucas KR, Rich PA, Polus BI. Muscle activation patterns in the scapular positioning muscles during loaded scapular plance elevation: The effects of latent myofascial trigger points. Clin Biomech 2010; 25(8): 765-770.
  9. Ge HY, Arendt-Nielsen L, Madeleine P. Accelerated muscle fatigability of latent myofascial trigger points in humans. Pain Med 2012; 13(7): 957-964.
  10. Ibarra JM, Ge HY, Wang c, et al. Latent myofascial trigger points are associated with an increased antagonistic muscle activity during agonist muscle contraction. J Pain 2011; 12(12): 1282-1288.