Pigmentation traits and inflammatory arthritis: Associations between eye and skin color, diagnosis, and treatment patterns

The aesthetic features of pigmentation, specifically eye and skin color, show a significant correlation with the biological etiology of autoimmune diseases, challenging traditional views. The present study assessed the interplay between pigmentation traits and diagnostic classification, as well as treatment strategies, within a population of patients afflicted with rheumatoid arthritis (RA), spondyloarthritis (SpA). A cross-sectional retrospective analysis was conducted involving 215 patients diagnosed with RA, ankylosing spondylitis (AS), or psoriatic arthritis (PsA). Ocular and cutaneous pigmentation (brown, blue, green; light vs dark shades), were recorded alongside demographic, diagnostic, and therapeutic data. A structural equation model (SEM) was employed to evaluate the impact of pigmentation on diagnostic and treatment outcomes. Individuals with darker skin tones were significantly associated with SpA diagnoses (β=-0.344, p<0.001). A modest association was found between eye color and diagnosis (β=0.282, p=0.037), and eye color also influenced treatment assignment (β=0.300, p=0.041). Sex remained the most influential factor for treatment allocation among all variables examined (β=0.947, p<0.001). An association was observed between pigmentation traits and diagnostic groupings, but not treatment allocation, suggesting a possible connection to the underlying pathophysiology. This research warrants further investigation into the genetic and immunological connections between pigmentation and autoimmune diseases.