Primary progressive multiple sclerosis: Tactile-associated functional MR activity in the cervical spinal cord

Purpose: To assess the extent of tactile-associated cervical spinal cord activation in patients with primary progressive (PP) multiple sclerosis (MS) and to investigate the relationship between spinal cord functional activation and the severity of cervical spinal cord and brain structural damage by using magnetic resonance (MR) images. Materials and Methods: The study was conducted with institutional review board approval. Written informed consent was obtained from each participant. Cervical spinal cord functional MR images were obtained in 23 patients with PP MS and 18 healthy control subjects during tactile stimulation of the right hand. Conventional and diffusion-tensor MR images of the brain and spinal cord were also acquired. Mean stimulus-related signal intensity change for all activated voxels and the distribution of functional MR activity at each spinal cord level were obtained. Univariate analysis was used to compare MR findings between groups. Between-group differences in topographic distribution of functional MR activity were evaluated by using randomeffects logistic regression models. Results: Patients with PP MS had higher mean spinal cord activity on functional MR images than did controls. A higher occurrence of functional MR activation in the right versus left side of the spinal cord and in the posterior versus anterior section of the spinal cord was found in both control subjects and patients with PP MS. Patients who were mildly disabled had a pattern of functional MR activity distribution similar to that of controls, but patients who were more severely disabled did not show differential activation between the right and left sides of the spinal cord. A higher occurrence of functional MR activity in the anterior section of the right side of the spinal cord at the level of the C6-7 intervertebral disk (P = .05) and the left side of the spinal cord at the level of the C7-T1 intervertebral disk (P = .03) was found in patients with PP MS than in control subjects. Mean spinal cord functional MR imaging signal intensity change correlated with spinal cord fractional anisotropy. Conclusion: Patients with PP MS showed tactile-associated cervical spinal cord overactivation. Spinal cord functional changes, possibly owing to injured interneurons, likely contribute to the complex process that leads to the accumulation of irreversible disability in patients with PP MS.