Ramin Schadlu

BASICS

DESCRIPTION

• Presumed ocular histoplasmosis syndrome (POHS) is an inflammatory condition associated with systemic infection by the fungus Histoplasma capsulatum. It may be unilateral or bilateral.

– POHS is most common in the Ohio and Mississippi River valleys, where H. capsulatum is endemic.

Geriatric Considerations

Elderly patients with coexisting age-related macular degeneration should be monitored closely due to the increased risk of choroidal neovascular membrane (CNVM).

EPIDEMIOLOGY

Incidence

Incidence of new cases of POHS is difficult to determine but has been approximated at 2 per 100,000 per year in an endemic area.

Prevalence

• The prevalence ranges from 1.6% to 5.3% in endemic areas based on epidemiologic data from the 1960s and 1970s.

• In endemic regions, up to 70% of the population demonstrate exposure to H. capsulatum and react positively to histoplasmin antigen skin testing (1).

RISK FACTORS

• Exposure to H. capsulatum is the major risk factor for developing POHS.

– 4.4% of those who are skin test positive to H. capsulatum have clinical findings consistent with POHS (1).

Genetics

The HLA subtypes DRw2 and B7 have been associated with POHS. This suggests that POHS is possibly an immune-mediated response to an infectious trigger (1).

GENERAL PREVENTION

Avoiding exposure to H. capsulatum by avoiding sites of possible contamination such as excavation sites, old buildings being demolished, bird habitats, and bat-infested caves may prevent infection.

PATHOPHYSIOLOGY

• Focal infection of the choroid with H. capsulatum and/or a chronic reaction to immunogenic remnants of the organism causes the choroidal lesions in POHS.

– Very little pathologic evidence exists implicating H. capsulatum in POHS.

ETIOLOGY

• H. capsulatum has been implicated by epidemiologic studies and antigen skin testing in the U.S.

• However, a study in the Netherlands found no immunologic evidence to support a relationship between the clinical findings of POHS and H. capsulatum or other endemic organisms (2).

COMMONLY ASSOCIATED CONDITIONS

CNVM, which can be vision threatening

DIAGNOSIS

HISTORY

• Patients are typically young or middle-aged and may be asymptomatic.

• Patients should be questioned about time spent in endemic areas.

PHYSICAL EXAM

• POHS may be unilateral or bilateral.

• The classic findings for POHS are as follows:

– Multiple, focal, discrete, atrophic choroidal scars in the macula or periphery (termed “punched-out” lesions or “histo spots”) can result from previous choroiditis or CNVM.

– Linear atrophic lesions may also be seen (“histo streaks”).

– Peripapillary atrophy (chorioretinal atrophy adjacent to the optic nerve)

– No cellular reaction in the anterior chamber or vitreous cavity

• Active and/or regressed CNVM may be seen in association with POHS. A fibrovascular disciform scar may also be seen as a remnant of prior CNVM.

– The development of CNVM is more likely in eyes with macular “histo spots.”

• Active areas of choroiditis may be seen.

DIAGNOSTIC TESTS & INTERPRETATION

Lab

• Laboratory testing is not generally indicated in patients with POHS, since it is a clinical diagnosis.

• Skin testing with histoplasmin antigen is generally no longer performed.

• In patients with ocular disease only, serum and/or urine antigen testing for H. capsulatum is unlikely to yield positive results.

• Serum antibodies to H. capsulatum can be detected in patients with a history of exposure to the organism.

Imaging

Initial approach

• Imaging tests are indicated to confirm the presence of CNVM.

– Fundus photographs

– Fluorescein angiogram

– Ocular coherence tomography

– Indocyanine green angiography

Follow-up & special considerations

Patients with POHS should be followed at least yearly for early detection of CNVM.

Pathological Findings

One study detected products of H. capsulatum DNA via polymerase chain reaction in 1 eye with POHS (3).

DIFFERENTIAL DIAGNOSIS

• Multifocal choroiditis with panuveitis

– Clinically similar to POHS but can be differentiated by the presence of a cellular reaction.

• Pathologic myopia

• Age-related macular degeneration

• Angioid streaks

• Idiopathic CNVM

• Other fungal choroiditis

• Bacterial choroiditis

• Viral choroiditis

TREATMENT

MEDICATION

• Medication is not indicated for most cases of POHS.

• Patients with choroiditis may be treated with oral or periocular steroid.

ADDITIONAL TREATMENT

Issues for Referral

• Patients with any suspicion of CNVM should be evaluated by a retinal specialist.

– Immunocompromised patients may develop disseminated histoplasmosis. Such cases should be referred to an infectious disease specialist.

Additional Therapies

• Thermal laser has been shown to be beneficial in CNVM secondary to POHS (1)[A].

– However, thermal laser to subfoveal or juxtafoveal lesions can cause a central scotoma, so alternative therapies should be explored.

• Photodynamic therapy can be beneficial for treatment of CNVM due to POHS. Patients typically require only 1 or 2 treatments and have good 2-year maintenance of treatment benefit (4)[A].

• Intravitreal bevacizumab has resulted in an increase in vision in 71% of eyes treated for CNVM due to POHS. Intravitreal bevacizumab should be considered especially in patients with subfoveal CNVM in whom other treatment modalities may lead to central scotoma (5)[A].

SURGERY/OTHER PROCEDURES

• In patients with extension of peripapillary CNVM into the subfoveal space, pars plana vitrectomy with removal of the CNVM may be beneficial. In a retrospective review, 15/17 patients had stabilization or improvement of their vision after a year or more (6)[B].

• The submacular surgery trial found that there was a benefit to surgery in patients with vision worse than 20/100, but this was before anti-VEGF therapy. There was a 58% recurrence rate.

IN-PATIENT CONSIDERATIONS

Initial Stabilization

In patients with disseminated histoplasmosis, a complete medical evaluation to determine organ involvement should be performed. Intravenous antifungals should be initiated.

Admission Criteria

Disseminated histoplasmosis may occur in immunocompromised patients. These patients require hospitalization and aggressive management.

ONGOING CARE

FOLLOW-UP RECOMMENDATIONS

Patients need regularly scheduled follow-up visits at least yearly. In patients with evidence of previous or active CNVM, more frequent follow-up is indicated.

Patient Monitoring

Patients should monitor their central vision daily with an Amsler grid. Any changes should be evaluated immediately.

PATIENT EDUCATION

Patients should be educated on the need for regular follow-up and daily Amsler grid monitoring.

PROGNOSIS

Visual prognosis can be good, as long as glaucoma and any posterior segment complications are controlled.

COMPLICATIONS

Permanent visual loss can occur secondary to CNVM.

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