Placoid lesions of the retina: progress in multimodal imaging and clinical perspective

Placoid lesions of the retina may be secondary to a wide spectrum of acquired inflammatory conditions that have been reported as single entities with different presentation and clinical course. These conditions include acute posterior multifocal placoid pigment epitheliopathy, persistent placoid maculopathy, serpiginous choroiditis, serpiginous-like choroiditis, relentless placoid chorioretinitis and acute syphilitic posterior placoid chorioretinitis. In this article, we will group these conditions under the name of 'placoids'. The recognition of the specific condition may be challenging in clinical practice, often resulting in diagnostic and therapeutic delay. Given the complex nature of placoids and their similarities, a systematic approach including differentiating between infectious and non-infectious aetiologies increases the chance of reaching the correct diagnosis. Detailed history and comprehensive clinical examination are the first steps to formulate a diagnostic hypothesis that should be corroborated by multimodal imaging and appropriate investigations. The advent of multimodal imaging has made it possible to extensively study placoids and revealed a constellation of specific findings that may help clinicians in the diagnostic process. The treatment of the conditions other than syphilis is complex and sometimes challenging. Our article is aimed at giving an overview of the individual entities associated with placoids and discussing the differential diagnosis. A practical and systematic approach is then proposed.