Placoid Retinopathies: Acute Posterior Multifocal Placoid Pigment Epitheliopathy, Serpiginous Choroiditis, Relentless Placoid Chorioretinitis, and Persistent Placoid Maculopathy

Acute posterior multifocal placoid pigment epitheliopathy (APMPPE), serpiginous choroiditis (SPC), relentless placoid chorioretinitis (RPC), and persistent placoid maculopathy (PPM) are grouped together due to the "placoid" nature of their lesions. They historically fall under a broader category of white spot diseases; however, their placoid lesions and time course often distinguish them from other entities. Historically, the pathophysiology of the lesions was not entirely understood, with a controversy of the primary site being the choroid or outer retina. Multimodal imaging has been instrumental in gaining insight to these processes and revealing a primary role of choroidal flow impairment. The role of autoimmunity remains uncertain. The placoid diseases resemble each other on clinical examination and imaging. Clinically, they are characterized by placoid outer retinal lesions. There is variable development of atrophy that is most severe in SPC as well as choroidal neovascularization, which occurs more commonly in SPC and PPM. There is evidence of choriocapillaris nonperfusion that corresponds with outer retinal changes along with some element of blockage of fluorescence. Optical coherence tomography shows backscatter and hyperreflectivity with loss of transparency of the outer nuclear layer and later development of thinning, loss of photoreceptors, and retinal pigment epithelium damage that tends to be more advanced in SPC and PPM. These entities can be differentiated by their time course, laterality, age distribution, and severity of permanent damage. APMPPE typically presents with a shorter disease course, while RPC confers a much more protracted course. In cases of foveal involvement, outcomes may vary with APMPPE having the most favorable prognosis and SPC carrying the poorest. All seem to respond to immunosuppression.