Proton magnetic resonance spectroscopy of the thalamus in patients with chronic neuropathic pain after spinal cord injury

Abstract

Background and purpose: Spinal cord injury (SCI) results in a number of consequences; one of the most difficult to manage is chronic neuropathic pain. Thus, defining the potential neural and biochemical changes associated with chronic pain after SCI is important because this may lead to development of new treatment strategies. Prior studies have looked at the thalamus, because it is a major sensory relay station. The purpose of our study was to define alterations in metabolites due to injury-induced functional changes in thalamic nuclei by using single-voxel stimulated echo acquisition mode MR spectroscopy.

Methods: Twenty-six men were recruited: 16 patients with SCI and paraplegia (seven with pain, nine without pain) and 10 healthy control subjects. Pain was evaluated in an interview, which included the collection of information concerning the location, quality, and intensity of pain, carefully identifing the dysesthetic neuropathic pain often seen in SCI. Localized single-voxel (8-cm(3) volume) proton spectra were acquired from the left and right thalami.

Results: The concentration of N-acetyl (NA) was negatively correlated with pain intensity (r = -0.678), and the t test showed that NA was significantly different between patients with pain and patients without pain (P =.006). Myo-inositol was positively correlated with pain intensity (r = 0.520); difference between patients with pain and those without pain was almost significant (P =.06).

Conclusion: The observed differences in metabolites in SCI patients with and pain and in those without pain suggest anatomic, functional, and biochemical changes in the thalamic region.

Fig 1.

Axial T1-weighted image shows the location of the 2 × 2 × 2-cm voxel in the region of the left thalamus and the corresponding location of the right thalamus. MR spectroscopic data were separately acquired from each voxel for the three groups: SCI patients with pain, SCI patients without pain, and healthy control subjects. Fig 2. Typical single-voxel stimulated echo acquisition mode spectrum from a healthy control subject. The assignment of peaks to various cerebral metabolites and the spectral analysis are described in Methods.