Features

First described in 1941, presumed ocular histoplasmosis syndrome (POHS), also known as ocular histoplasmosis or ocular histoplasmosis syndrome, has been debated as a separate condition from multifocal chorioretinitis and punctate inner choroidopathy due to a presumed precursor fungal infection. The dimorphic fungus Histoplasma capsulatum is the strongly theorized infectious agent based on skin testing for histoplasmin in affected individuals, increased reports of POHS in endemic areas of the protozoan, and reports of histoplasmosis deoxyribonucleic acid found in affected enucleated eyes. Ocular disease is believed to arise after inhalation of spores into the lungs, ultimately resulting in hematogenous dissemination. POHS is controversially linked to endemic areas of the Unites States, including Ohio and Mississippi (the “histo belt”) but has been reported throughout the United States and Europe. Numerous theories exist on POHS pathogenesis. One theory includes the choroid being involved via hematogenous transmission at the time of the initial systemic infection. As the focal chorioretinitis resolves, atrophic chorioretinal scars develop. The loss of retinal pigment epithelium (RPE) and Bruch’s membrane may result in choroidal neovascularization (CNV). Fragile choroidal neovascular vessels lack proper functioning tight junctions, resulting in leakage of fluid, lipid exudate, and hemorrhages. Chronic remodeling with fibrovascular scarring can subsequently occur, resulting in profound central vision loss when the fovea is affected. The cause of patient-to-patient variation in the initiation of CNV is unknown, with possible underlying genetic predisposition implications based on human leukocyte antigen (HLA)-DRw2 typing. Additional theories for CNV predisposition include hypersensitivity reaction, reinfection, or a larger initial fungal inoculation.

62.1.1 Common Symptoms

Ocular

Often asymptomatic; may be diagnosed incidentally during routine eye examinations. Manifestations can be wide-ranging, depending on the severity and location of chorioretinal lesions. Fovea-involving maculopathy may cause metamorphopsia and central vision loss.

Systemic

Depends on the severity of the exposure and immune status of the host. Most commonly, mild flu-like respiratory symptoms may occur in immunocompetent patients that are not typically diagnosed.

62.1.2 Exam Findings

Clinical diagnosis is based on having two or more findings of the triad of small atrophic, “punched-out” chorioretinal lesions (histo spots), peripapillary atrophy or pigment changes, and maculopathy due to CNV (▶ Fig. 62.1, ▶ Fig. 62.2). Vitreous inflammation, or vitreous cell, is absent. Atrophic lesions tend to be smaller than the optic disc, located in the macula or periphery, asymmetric, and often asymptomatic. CNV sequelae include subretinal and intraretinal hemorrhages, subretinal fluid, and late fibrovascular disciform scarring.

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