Pseudo-Choroidal Melanocytosis in Birdshot Chorioretinitis: A Case Series from a Prospective Cohort

To describe cases of birdshot chorioretinitis (BSCR) with fundi resembling choroidal melanocytosis and to explore possible pathophysiological mechanisms.

Patients were selected from the prospective CO-BIRD cohort (NCT05153057), if ultra-widefield fundus imaging (UWF, Optos, Optomap®) demonstrated alternating, well-demarcated light- and dark-appearing fundus zones, described here as pseudo-choroidal melanocytosis (PCM). The collected data included best-corrected visual acuity (BCVA), visual field, quality of life, and multimodal imaging. Dark-appearing areas were quantified across time points using a fundus lesion delineation tool.

Among 1016 eyes (508 patients), PCM was observed in 8 eyes from 4 patients (1.0%). All cases were bilateral and included the macula. The dark-appearing fundus regions expanded in all cases (median progression rate: 1124.6 pixels²/year [536.5-2293.1]), contiguous with adjacent pigmentation. Optical coherence tomography (OCT) revealed a transition from homogeneous hyporeflectivity within light-appearing areas to mottled hyperreflectivity within dark-appearing zones, with varied changes in choroidal thickness. Two patients were managed conservatively, while two required long-term immunosuppression. None developed macular oedema or choroidal neovascularisation during their follow-up.

PCM represents a rare fundus manifestation of BSCR and expands the spectrum of its phenotypic presentations. It may represent an intermediate state along a continuum ranging from atrophic chorioretinal lesions to pseudo-albinism. The preferential reappearance of pigmentation adjacent to structurally preserved retina and choroid may reflect melanocyte migration or reactivation from neighboring healthy tissue. The contribution of melanocytes to the immunopathogenesis of BSCR warrants further investigation.