Assessing "occult'' cervical cord damage in patients with neuropsychiatric systemic lupus erythematosus using diffusion tensor MRI

Background: Whereas focal and diffuse brain damage on conventional MRI is seen in patients with neuropsychiatric systemic lupus erythematosus (NSLE), the spinal cord seems to be rarely involved. Diffusion tensor (DT) MRI provides information on the patterns of tissue disruption of the central nervous system, which may go undetected by conventional MRI. Objective: To quantify the extent of otherwise "occult'' injury of the cervical cord in NSLE, and to improve our understanding of its nature. Subjects and methods: Conventional and DT MRI scans of the cervical cord and brain were acquired from 11 patients with NSLE and 10 healthy controls. Histograms of mean diffusivity ( MD) and fractional anisotropy ( FA) of the cervical cord and brain were analysed. Measures of cervical cord and brain atrophy and focal lesion loads were computed. Results: Only one patient had a single focal lesion of the cord whereas all had multiple brain lesions on conventional MRI scans. Cord and brain volumes did not differ between patients and controls. Mean peak height of the cervical cord MD histogram (p = 0.0001) and average brain FA ( p = 0.001) were significantly lower in patients than in controls. Average cord MD was correlated with average brain MD (r = 0.69, p = 0.01) and FA (r = -0.81, p = 0.002). Conclusion: DT MRI shows mild and otherwise "occult'' cord damage in NSLE, which might be secondary to Wallerian degeneration of long tract fibres passing trough damaged areas of the brain.