Research Review By Gary Maguire, M.Sc., P.T.©

Date Posted:

May 2010

Study Title:

Bilateral Mechanical-Pain Sensitivity over the Trigeminal Region in Patients with Chronic Mechanical Neck Pain

Authors:

La Touche R et al.

Author's Affiliations:

Faculty of Medicine, Department of Physical Therapy; University Center for Clinical Research of the Craneal-Cervical-Mandibular System, Universidad San Pablo CEU, Madrid, Spain.

Publication Information:

The Journal of Pain 2010; 11(3): 256-263.

Background Information:

Chronic mechanical neck pain is a significant clinical problem. Some suggest that the prevalence of neck pain is as high as the prevalence of low back pain. The literature indicates a rating of self-reported neck pain in the general population of 146-213 per 1,000 patients per year. There is also evidence in the United States that management of neck pain is second only to low back pain in annual worker’s compensation costs.

Nearly half of neck-pain patients develop chronic symptoms and many will continue to exhibit moderate disability at long-term follow-up. While there is ongoing debate over the etiology of insidious mechanical neck pain, it is clear that it is multifactorial in nature, with both physical and psychosocial contributors.

In recent years there has been a growing interest in the study of nociceptive-pain processing in different musculoskeletal-pain conditions. The phenomenon of sensory hypersensitivity has been recently investigated in mechanical non-traumatic neck pain (1). Hypersensitivity present in individuals with idiopathic neck pain seems to be confined to the neck area with little evidence of spread to more remote body regions. This hypersensitivity restricted to the neck region may reflect segmental local sensitization, but not wide-spread central sensitization (2).

The expansion of symptoms from the neck area to the trigeminal region may be related to the convergence of the nociceptive second-order neurons receiving both trigeminal and cervical inputs into the trigemino-cervical nucleus caudalis in the spinal gray matter of the spinal cord.

This study investigated trigeminal sensitization in patients with chronic mechanical neck pain by evaluating pressure pain thresholds (PPT) the trigeminal region, cervical spine, and tibialis anterior, while controlling for psychological aspects such as depression and anxiety. Previous literature has demonstrated that psychological states, particularly anxiety and depression, can induce an increased effect on pressure-pain sensitivity.

Pertinent Results:

Forty patients were screened for possible eligibility criteria and seventeen patients were excluded. Therefore, data was collected from 23 patients (10 males, 13 females) with mechanical neck pain as well as 23 matched controls. No significant differences were noted between groups.

Findings:
  • Positive correlations were noted between the duration of symptoms and intensity of perceived pain and self-reported depression.
  • A positive correlation was also noted between pain intensity and self-reported disability and self-reported depression.
  • Between groups, significant differences for PPT indices were noted between anatomical sites (masseter, temporalis, cervical spine) but not between sides.
  • Significant differences were noted for both masseter and temporalis muscles – with neck pain patients displaying lower PPT (and hence, higher sensitivity) than controls (P < 0.001).
  • Patients also displayed lower PPT values in the upper trapezius and C5/6 joint (P < 0.001) compared to controls
  • Overall – the cervical region (trapezius and C5/6) showed lower PPT values (and hence higher sensitization) than the trigeminal points (masseter and temporalis) in the patient group.
  • Pain duration and intensity were both correlated with lower masseter PPT values in neck pain patients.
  • Although female subjects had lower PPTs overall – no significant differences were noted between groups in PPT over the tibialis anterior muscle (P = 0.824)
  • Intraexaminer repeatability of the PPT measurements was good – ranging from 0.89-0.93 for all regions.

Clinical Application & Conclusions:

The study showed bilateral pressure-pain hyperalgesia (hypersensitivity) in both the trigeminal and cervical region, but not over the tibialis anterior muscle, in patients with mechanical chronic neck pain as compared to a control group. In agreement with previous literature, these findings support the idea that mechanical non-traumatic neck pain is characterized by pressure-pain hyperalgesia in the cervical spine, probably reflecting peripheral nociceptor sensitization.

It was also concluded that patients in this study with mechanical chronic neck pain also have pressure-pain hyperalgesia in the trigeminal region. This may suggest a sensitization process affecting the trigemino-cervical nucleus caudalis due to the convergence of inputs from the trigeminal and cervical regions. The absence of sensitization over the tibialis anterior muscles furthers the evidence that non-traumatic neck pain is characterized by segmental, but not widespread, sensitization mechanisms that are mostly restricted to the trigemino-cervical region.

The decrease in pressure pain thresholds in the trigeminal region was associated with the intensity and duration of neck-pain, supporting the role of peripheral nociceptive input as a driving factor for inducing sensitization.

Clinicians should note that this study lends support to the idea that non-traumatic neck pain can be associated with sensitization in the trigemino cervical region. Clinically this is important when assessing spreading symptomatology. Further, such spreading could be monitored utilizing PPT during treatment to evaluate progress or exacerbation of symptoms.

Study Methods:

Twenty-three patients with neck pain (56% female), aged 20 to 37 years old, and 23 matched controls (aged 20 to 38 years) were included. Inclusion criteria consisted of mechanical neck pain - defined as generalized neck and/or shoulder pain with symptoms provoked by neck postures, neck movement, or palpation of the cervical musculature. Symptoms had to be bilateral and present for at least 6 months. The control group consisted of healthy volunteers screened for the absence of neck pain, systemic disease or any history of traumatic event.

Pressure pain threshold (PPT) is defined as the minimal amount of pressure where a sensation of pressure first changes to pain. The study utilized a mechanical pressure algometer, mean of 3 trials for rater reliability with a 30 second resting period allowed between each trial. Reliability of pressure algometry has been found to be high in both asymptomatic subjects and neck pain patients (4). The study protocol was the same for both groups and order of assessment was randomized between the subjects.

PPT was measured bilaterally over masseter and temporalis muscles, the articular pillar (C5/6 zygapophyseal joint), the upper trapezius muscle and tibialis anterior. A greater PPT index (%) indicates a lower degree of sensitization. Data analysis was performed utilizing the SPSS statistical package v. 16.0.

The sample-size calculations were based on detecting, at the least, significant differences of 20% on pressure pain threshold (PPT) between both groups (3). The data consisted of the magnitude of sensitization by assessing the differences of absolute and relative PPT values between both groups.

Study Strengths / Weaknesses:

The neck pain patients in this study were completely asymptomatic in the orofacial region, which suggests the reduced PPT demonstrated represents a sensitization process.

However, this study was limited by a small-ish sample size, something that plagues most studies of this nature. Further, the authors appropriately noted that the lower PPT levels over the upper trapezius were may have reflected the presence muscle “spasms” or “tightness” in this area, which as we know is very common in this patient population.

Additional References:

  1. Sterling M. Testing for sensory hypersensitivity or central hyperexcitability associated with cervical pain. JMPT 2008; 31: 534-539.
  2. Scott D et al. Widespread sensory hypersensitivity is a feature of chronic whiplash-associated disorder but not chronic idiopathic neck pain. Clin J Pain 2005; 21: 175-181.
  3. Prushansky T et al. Reproducibility indices applied to cervical pressure pain threshold measurements in healthy subjects. Clin J Pain 2004; 20: 341-347.
  4. Chesterson et al. Inter-rater reliability of algometry in measuring pressure pain thresholds in healthy humans, using multiple raters. Clin J Pain 2007; 23: 760-766.