Pyoderma gangrenosum: From historical perspectives to emerging investigations.

Pyoderma gangrenosum (PG) is a rare disease of unknown aetiology, first described over a century ago. Initially thought to have an infectious cause, and now primarily considered an autoinflammatory condition, PG continues to be poorly understood, commonly misdiagnosed, and difficult to treat. In this review, we discuss the journey of our understanding of PG to date, including first descriptions, challenges with diagnosis, presumed pathogenesis, and treatments used. We highlight major historical landmarks and their importance, explain the rationale behind current investigations, note outstanding gaps in knowledge, and explore the future directions of PG research. We summarise what we have known, what we are working on knowing, and what we have yet to explore about PG, illustrating overall trends to invigorate future research.