Ocular Histoplasmosis

Systemic Findings

Histoplasma capsulatum, a fungus found worldwide in valleys with rivers, is endemic to the midwestern United States. Found in the soil, it is readily inhaled and phagocytosed. Although histoplasmosis may start in the lungs, it can spread to the liver and the spleen, leaving small calcified lesions that can be seen on x-ray examination. The disease can take three major forms: a nonfatal acute pneumonitis with fever; an acute progressive form that can be fatal in 1 to 2 months; and a chronic form similar to tuberculosis. These disease presentations rarely have ocular manifestations. Ocular histoplasmosis syndrome is a rather distinct entity found almost exclusively in the United States, and it usually occurs in symptom-free persons living in endemic regions. However, a similar clinical entity has been seen in nonendemic regions both in the United States and in other countries.

Ocular Appearance

It was probably Reid et al. who described the first ocular case that we now recognize as ocular histoplasmosis syndrome, but Woods and Wahlen were the first to describe this ocular syndrome in full detail. They believed that H. capsulatum might be the cause of both the typical atrophic spots in the retinal periphery and the disciform changes in the macula. Although the disorder is found most commonly in the midwestern United States, particularly in the Ohio–Mississippi River valleys, it also appears in the Middle Atlantic states, such as Maryland. In these areas, skin tests for histoplasmosis show positive results in a high percentage of the population, indicating systemic sensitization by the immune system. Ocular histoplasmosis syndrome is a rare disease in other parts of the world, even in areas endemic for histoplasmosis. From countries other than the United States, there are reports of patients with symptoms that meet the criteria for the diagnosis; however, test results are negative for evidence of histoplasmosis infection and sensitization. ^,

Studies in the United States have suggested that typical findings of ocular histoplasmosis will be found in 1.6% to 12.9% of the population in an endemic area. Furthermore, Smith and Ganley determined from the study in Walkersville, Maryland, that maculopathy caused by ocular histoplasmosis will develop in 1 of 1000 adults in an endemic area. The disease appears most commonly in the third to fourth decades of life, with men more likely to have involvement of both maculae. It appears that the disease is considerably less common in African Americans ( Box 16.1 ). H. capsulatum causes four major clinical manifestations of the ocular disease: “histo” spots, maculopathy, peripapillary pigment changes, and clear vitreous.