To identify characteristics on multimodal imaging (MMI) in idiopathic multifocal choroiditis (MFC) that can identify inflammatory activity and distinguish choroidal neovascularization (CNV) activity from inflammatory activity.

Prospective cohort study.

MMI consisted of spectral-domain optical coherence tomography (angiography) (SD-OCT(A)), fundus autofluorescence, fundus photography, infrared imaging, fluorescein angiography (FA), and indocyanine green angiography (ICGA). MMI characteristics obtained during active and inactive disease were compared within the same lesion. Secondly, MMI characteristics were compared between active inflammatory lesions with and without CNV activity.

Fifty patients (110 lesions) were included. In 96 lesions without CNV activity, the mean focal choroidal thickness was increased during the active disease (205 µm) compared to the inactive disease (180 µm) (P ≤ .001). Lesions with inflammatory activity typically demonstrated moderately reflective material located in the sub–retinal pigment epithelium (RPE) and/or in the outer retina with disruption of the ellipsoid zone. During the inactive stage of the disease, the material disappeared or became hyperreflective and indistinguishable from the RPE. During the active stage of the disease, the area of hypoperfusion in the choriocapillaris significantly increased as visualized on both ICGA and SD-OCTA. CNV activity in 14 lesions was associated with subretinal material with a mixed reflectivity and hypotransmission of light to the choroid on SD-OCT and leakage on FA. SD-OCTA identified vascular structures in all active CNV lesions and in 24% of lesions without CNV activity (showing old, quiescent CNV membranes).

Inflammatory activity in idiopathic MFC was associated with several MMI characteristics, including focally increased choroidal thickness. These characteristics can guide clinicians in the challenging process of the evaluation of disease activity in idiopathic MFC patients.