Chronic myofascial temporomandibular pain is associated with neural abnormalities in the trigeminal and limbic systems

Abstract

Myofascial pain of the temporomandibular region (M-TMD) is a common, but poorly understood chronic disorder. It is unknown whether the condition is a peripheral problem, or a disorder of the central nervous system (CNS). To investigate possible CNS substrates of M-TMD, we compared the brain morphology of 15 women with M-TMD to that of 15 age- and gender-matched healthy controls. High-resolution structural brain and brainstem scans were carried out using magnetic resonance imaging (MRI), and data were analyzed using a voxel-based morphometry approach. The M-TMD group evidenced decreased or increased gray matter volume compared to controls in several areas of the trigeminothalamocortical pathway, including brainstem trigeminal sensory nuclei, the thalamus, and the primary somatosensory cortex. In addition, M-TMD individuals showed increased gray matter volume compared to controls in limbic regions such as the posterior putamen, globus pallidus, and anterior insula. Within the M-TMD group, jaw pain, pain tolerance, and pain duration were differentially associated with brain and brainstem gray matter volume. Self-reported pain severity was associated with increased gray matter in the rostral anterior cingulate cortex and posterior cingulate. Sensitivity to pressure algometry was associated with decreased gray matter in the pons, corresponding to the trigeminal sensory nuclei. Longer pain duration was associated with greater gray matter in the posterior cingulate, hippocampus, midbrain, and cerebellum. The pattern of gray matter abnormality found in M-TMD individuals suggests the involvement of trigeminal and limbic system dysregulation, as well as potential somatotopic reorganization in the putamen, thalamus, and somatosensory cortex.

Figure 1. Regions of greater gray matter volume in the brains of individuals with chronic myofascial temporomandibular pain contrasted with controls

Regions of greater gray matter volume (orange) are displayed on an MNI-normalized average of all student participant’s brain images (N = 29). All slices are axial; anterior is at top. Significant areas include (left pane, anterior to posterior) the right inferior frontal gyrus, right anterior insula, right globus pallidus, right thalamus, left thalamus, and (right pane) right posterior putamen.

Figure 2. Regions of greater gray matter volume in the pons of individuals with chronic myofascial temporomandibular pain

On the top pane, regions of greater gray matter volume (yellow) are displayed on an MNI-normalized average of all study participant’s brainstem images (N = 29). A single axial slice is shown at the level of the trigeminal nuclei (MNI plane −25 mm from the AC/PC line). The image has been rotated 180° to match the reference image (bottom pane), with the anterior (ventral) aspects of the pons at the bottom. Significant clusters are seen in the bilateral sensory or motor trigeminal nuclei. A third, unilateral cluster is seen, approximately in the area of the medial lemniscus. On the bottom pane, a reference image of the same slice and orientation is provided, with locations of major structures. (Image reprinted from Netter 2007, page 122).

Figure 3. Self-reported jaw pain severity in M-TMD patients is associated with reduced regional gray matter volume

The left pane shows a region of the rostral anterior cingulate cortex (inferior cluster) where gray matter volume is negatively associated with jaw pain (e.g., greater jaw pain associated with less gray matter volume). A single sagittal slice is shown (x = +2). Reduced volume is also seen in the superior frontal gyrus (superior cluster). In the right pane, a scatterplot shows the relationship between jaw pain, and gray matter volume in the rostral anterior cingulate of patients.