Rheumatoid arthritis (RA) is a chronic inflammatory disease that alters the body over time through pain, stiffness, and joint deformity. Before the development of effective medical treatments, the bodily consequences of such conditions were lived and observed within everyday life, and at times recorded through visual culture. In this context, artworks provide a valuable perspective on illness beyond formal clinical description. Pierre-Auguste Renoir, who later developed severe RA, represents a compelling figure at the intersection of art and chronic disease. This study examines Renoir’s painting In Summer , depicting his model and companion Lise Tréhot, through an iconodiagnostic and art-historical approach informed by the literature on RA-related hand involvement. The visual analysis identifies subtle, non-specific features suggestive of inflammatory joint change. However, comparison with other contemporary depictions of the same model highlights the limitations of retrospective interpretation and cautions against definitive diagnostic claims. Rather than proposing a diagnosis, this study reflects on how artworks may register bodily variation, vulnerability, and illness in ways that precede clinical classification. By integrating art history and medicine, it underscores the role of visual artworks as cultural documents within medical humanities and their potential value in medical education.