Systemic lupus erythematosus (SLE) with central nervous system (CNS) involvement is frequent and can have high morbidity. The primary pathophysiology of SLE in the CNS is thought to be inflammation secondary to autoantibody-mediated vasculitis. Neuroimaging studies have reported hypometabolism (impending cell failure) and atrophy (late-stage pathology), but not inflammation. We used a validated index of SLE-related disease activity as a regressor for positron emission tomographic (PET) images of glucose uptake to detect the presence and regional distribution of inflammation (hypermetabolism) and tissue failure, apoptosis or atrophy (hypometabolism).
Eighty-five newly diagnosed SLE patients without focal neurological symptoms were studied. Disease activity was quantified using the SELENA SLE Disease Activity Index (SS). 18Fluoro-deoxy-glucose (FDG) PET images were analyzed by visual inspection and as group statistical parametric images using the SS score as the analysis regressor.
SS-correlated increases in glucose uptake were found throughout the white matter, most marked in heavily myelinated tracts. SS-correlated decreases were found in frontal and parietal cortex, in a pattern similar to that seen by visual inspection and in prior reports of hypometabolism.
We interpret the SS-correlated increases in glucose consumption as potential evidence of inflammation, in keeping with prior reports of hypermetabolism in inflammatory disorders. To our knowledge, this is the first imaging evidence of SLE-induced CNS inflammation in an SLE inception cohort. The dissociation between 18FDG uptake characteristics, spatial distribution, and correlation with disease activity argues that glucose hyper- and hypometabolism reflect fundamentally different aspects of the pathophysiology of CNS SLE.
Keywords: systemic lupus erythematosus, positron emission tomography, glucose metabolism, SLEDAI, inflammation