DTI detects water diffusion abnormalities in the thalamus that correlate with an extremity pain episode in a patient with multiple sclerosis☆

BACKGROUND Various types of multiple sclerosis (MS) related pain have been discussed. One concept is that deafferentation secondary to lesions in the spino-thalamo-cortical network can cause central pain. However, this hypothesis is somehow limited by a lack of a robust association between pain episodes and sites of lesion location. OBJECTIVE We tested the hypothesis that temporary tissue alterations in the thalamus that are not detectable by conventional magnetic resonance imaging (T1w, FLAIR) can potentially explain a focal, paroxysmal central pain episode of a patient with MS. For microstructural tissue assessment we employed ten longitudinal diffusion tensor imaging (DTI) examinations. RESULTS We could demonstrate an abnormal, unilateral temporary increase of the fractional anisotropy (FA) in the thalamus contralateral to the affected body side. Before the pain episode and after pain relief the FA reached completely normal values as seen in identically investigated age and gender matched 100 healthy control subjects. CONCLUSION THESE FINDINGS SUGGEST THAT: i.) frequently applied and quantitatively evaluated DTI could be used as a sensitive imaging technique for detection of pathological processes associated with MS not detectable with conventional imaging strategies, ii.) temporary pathological processes in the "normal-appearing" thalamus may explain waxing and waning symptoms like episodes of central pain, and iii.) cross-sectional case examinations on (MS) patients with central pain should be performed to investigate how often thalamic alterations occur together with central pain.