To determine whether intrathalamic tissue integrity measured using diffusion tensor imaging (DTI) is impaired early in the disease in a cohort of pediatric-onset MS patients imaged prior to cognitive and physical impairment.

The thalamus is composed of multiple regions, each with connections to cortical and subcortical areas that serve specific functions. Prominent thalamic volume loss has been reported in pediatric-onset MS (POMS). However, intra-thalamic tissue integrity has not been studied. 

64 direction DTI scans collected at York University using a 3T scanner with 32 channel head coil, were analyzed from 31 healthy controls (mean age=18 yrs, SD=3; 25 females) and 23 pediatric-onset MS patients (mean age=18 yrs, SD=3; 17 females, median EDSS 1.5, range 1-6). Mean fractional anisotropy (FA), mean and radial diffusivity (MD and RD) values were extracted from seven thalamic connectivity based regions - primary motor, sensory, occipital, prefrontal, premotor, posterior parietal, temporal and whole thalamus (identified using Oxford thalamic connectivity atlas) and compared between groups.

Whole-thalamus MD was significantly reduced in MS (p < 0.0005) while FA was modestly reduced in MS compared to healthy controls (p = 0.06). Of the regions analyzed, FA was reduced in the occipital and temporal connectivity regions in MS patients (p < 0.0005). MD and RD of the occipital, posterior-parietal, temporal (p < 0.0005 uncorrected) and pre-frontal (p < 0.001) regions were increased in the MS group. Total normalized thalamic volume was smaller in MS patients (p < 0.0005) but total brain volume did not differ between the groups. 

Intrathalamic tissue is compromised in pediatric-onset MS, supporting loss of thalamic structural integrity as an early aspect of MS pathobiology. Further studies will evaluate thalamocortical tracts to define their relationships with thalamic integrity and cognitive and clinical outcomes.