To assess in vivo volumetric and inflammatory changes of the choroid plexuses (CPs) in multiple sclerosis (MS).

The CPs are a blood-cerebrospinal fluid interface with key immunosurveillance functions. Experimental studies have suggested a role for CPs in experimental autoimmune encephalitis, but we lack in vivo evidence in patients with MS.

97 patients with MS (61 relapsing-remitting, RRMS, 36 progressive, PMS) and 44 age- and sex-matched healthy controls (HC) underwent 3T MRI; a subgroup of 37 patients and 19 HC underwent translocator protein (TSPO) ¹⁸F-DPA-714 PET to quantify neuroinflammation. The CPs of the lateral ventricles were manually segmented on 3D T1-weighted images for volumetric analysis. Whole brain, thalamus, normal-appearing white matter (NAWM), and cortex were segmented with Freesurfer.  T2-hyperintense and gadolinium-enhancing lesions were manually contoured. ¹⁸F-DPA-714 distribution volume ratio was quantified in parenchymal brain ROIs, whereas standardized uptake value was used for CP. Multivariable linear regressions adjusted for age, sex, brain volume, treatment and TSPO affinity were used to assess: i) differences in CP volume or ¹⁸F-DPA-714 uptake between patients and HC; ii) correlations of CP volume with brain volumes, WM lesion load, gadolinium enhancement, and parenchymal¹⁸F-DPA-714 uptake. 

CPs were 35% larger in MS compared to HC (P=.004). Subgroup analysis confirmed CP volume increase at the RRMS stage (P=.008). CP enlargement correlated with brain volume (r²:-0.33;P=.004), was higher in patients with gadolinium-enhancing lesions (P<.001), and correlated with brain inflammation as reflected by WM lesion load (r²:0.39;P<.001), ¹⁸F-DPA-714 binding in the thalami (r²:0.44;P=.04) and the NAWM (r²:0.5;P=.005). Finally, patients showed 17.5% higher CP ¹⁸F-DPA-714 uptake (P=.016), which correlated with CP volume in RRMS (r²:0.58;P=.01). 

CPs are enlarged and inflamed in MS, particularly during the RRMS stage, and this enlargement is associated with more inflammatory profiles. CP volumetric analysis could represent a novel imaging marker in MS.