Presumed Ocular Histoplasmosis Syndrome Workup

Updated: Sep 20, 2018
  • Author: Lihteh Wu, MD; Chief Editor: C Stephen Foster, MD, FACS, FACR, FAAO, FARVO  more...
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Workup

Laboratory Studies

Although the diagnosis of presumed ocular histoplasmosis syndrome is clinical, certain ancillary tests help in confirming it. Other than fluorescein angiography (FA), most patients do not require ancillary testing.

HLA typing B7 and DRw2 may be indicated.

Complement fixing antibodies are only positive in 16-68% of patients with POHS.

Lymphocyte stimulation assay by Histoplasma antigens may be indicated.

Focal calcifications in the liver or the spleen may be present.

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Imaging Studies

FA is essential in diagnosing and managing the maculopathy associated with POHS with photodynamic therapy or laser photocoagulation. The typical angiographic pattern is early hyperfluorescence with late leakage. According to its location relative to the center of the fovea, CNV has been classified as extrafoveal (200-1500 µm), juxtafoveal (1-199 µm), and subfoveal (under the center of the fovea).

Since the advent of anti-VEGF therapy for CNV secondary to the POHS, optical coherence tomography imaging is of paramount importance in the diagnosis and follow-up. [21] Any signs of continued exudation, such as intraretinal or subretinal fluid, is usually an indication for continued anti-VEGF treatment.

Chest radiography findings usually reveal calcifications of the hilar areas.

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Other Tests

Skin testing should not be performed on patients with a maculopathy; some report that it may exacerbate this condition.

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Histologic Findings

Few cases report H capsulatum isolated from the human eye. In most cases, isolation of the organism in either atrophic scars or CNV is not possible. Histologically, the peripapillary and peripheral spots are seen as areas where there is partial loss of the RPE and the photoreceptor cell layer. The Bruch membrane often presents with focal breaks in it. Sometimes, the overlying inner retina shows cystic degeneration. These areas often are surrounded by a lymphocytic choroidal infiltrate.

In the macular area, most CNV develops adjacent to an atrophic histo spot, although de novo neovascularization can occur. The new capillaries and fibroblasts originate from the choroid and grow through a defect in the Bruch membrane into the subretinal space, not the sub-RPE space (type 2 CNV). Reactive hyperplastic RPE is present at the advancing edge of CNV.

Specimens obtained during surgical excision of CNV reveal that the most common cellular components are vascular endothelium and RPE; they were present in more than 85% of samples. Fibrocytes and macrophages have been identified in more than 50% of specimens. Extracellular components include collagen and fibrin.

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