MRI Measures as Predictors of Working Memory Performance in Systemic Lupus Erythematosus
Spelman, Megan Elizabeth
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Working memory (WM) deficits have been reported in patients with systemic lupus erythematosus (SLE). It has also been reported that SLE patients may have disrupted central nervous system integrity (CNS). No studies have yet examined the relationship between working memory (WM) performance on an n-back task and microstructural and macrostructural brain damage in SLE. The present study examined whether there is a relationship between specific types of brain damage as measured by nonconventional and conventional MRI and WM performance in SLE patients. Methods: A visual n-back task was administered to 42 patients with SLE and 36 healthy controls (HCs). These participants were scanned on a 3T MRI using a multimodal imaging approach. Behavioral measures of n-back performance were also obtained. T-tests were used to determine MRI-specific group differences between SLE and HCs. Regression analyses were used to measure the relationship between MRI measures and individual differences in SLE patients on n-back performance for varying levels of WM load. MRI measures included lesion burden, tissue-specific atrophy, magnetization transfer imaging (MTI) and diffusion tensor imaging (DTI). Results: SLE patients had fewer correct responses on higher WM load conditions (2-back) and delayed information processing speed (RT) across all n-back conditions (0-, 1-, and 2-back). Compared to HCs, SLE patients displayed reduced gray matter volume (GMV), neocortical volume (NCV), thalamus volume, amygdala volume, whole brain fractional anisotropy (FA) normal appearing brain tissue FA (NABT FA), and increased normalized lateral ventricular volume (nLVV) and normal appearing white matter radial diffusivity (NAWM RD). Regression relationships were assessed for SLE patients only. Conventional MRI measures showed that increased nLVV, reflective of atrophy, was associated with increased RT on the 0-back. Non-conventional measures showed that decreased normal appearing white matter fractional anisotropy (NAWM FA) was associated with decreased accuracy on the 1-and 2-back conditions, while decreased NABT FA was associated with decreased accuracy on all three conditions (0-, 1-, and 2-back). Whole brain magnetization transfer ratio (MTR) was associated with slowed processing speed (increased reaction time, RT) on all three conditions (0-, 1-, 2-back), and mean normal appearing gray matter MTR (NAGM MTR) was associated with increased RT only on the 1- and 2-back conditions. Conclusions: Microstructural damage, particularly measured by MTR and FA, indicative of both white and gray matter involvement, was associated with impaired WM performance on a visual n-back task in SLE patients.