To determine if traumatic brain injury (TBI) contributes to the oral lower Symbol Digit Modalities Test (SDMT) scores we previously reported in Black and Hispanic patients with newly diagnosed multiple sclerosis (MS) compared to white patients. 

The MS Sunshine Study found that Black and Hispanic participants with newly diagnosed MS had lower oral SDMT scores than white participants but that this difference was best explained by underlying population differences rather than disease severity. TBI has been correlated with lower SDMT scores. Rates of TBI are higher and rehabilitative care for TBI is provided less often in Black and Hispanic people residing in the US. 

We studied 1,172 adults (553 incident MS, 619 controls) who enrolled in the MS Sunshine Study. Detailed TBI histories were obtained during the structured in-person interview. TBI was classified as Mild A (no loss of consciousness, LOC, but with concussive/post-concussive symptoms), Mild B (LOC for <30 minutes), Moderate (LOC >30min and <24 hours) or Severe (LOC >24 hours). Multivariable regression was used to examine correlates of SDMT scores.

103 (9%) participants reported a history of at least one TBI with maximum severity of Mild A, 190 (16%) Mild B, 29 (2%) Moderate and 8 (0.7%) Severe. There was no significant difference in frequency or severity of TBIs across racial or ethnic groups or by case/control status. There was no significant correlation between any category of TBI and SDMT scores, nor did accounting for TBI modify the correlation between having MS, being Black or Hispanic and lower SDMT scores.