Updated: Jul 24, 2007
Presumed ocular histoplasmosis syndrome (POHS) is a distinct clinical entity that is characterized by peripheral atrophic chorioretinal scars, peripapillary scarring, and maculopathy. This condition is believed to be secondary to exposure to Histoplasma capsulatum, although this fungus rarely has been isolated or cultured from an eye with the typically associated clinical findings.
Epidemiologic findings link the fungus to this condition. Based on skin tests in the United States, a similar geographic distribution of the fungal infection and POHS exists. Histoplasmin skin testing may exacerbate the ocular condition. Visual loss in POHS is secondary to the development of macular choroidal neovascularization (CNV).
H capsulatum is a dimorphic pathogenic fungus that often grows in soil around old chicken houses and areas harboring bats, such as caves. Large numbers of spores are dispersed into the air when contaminated soil is disturbed (eg, spelunking, raking). Exposure occurs when spores are inhaled.
In a normal host, the initial infection is usually asymptomatic or feels like influenza. In a few patients, a chronic cavitary pulmonary disease may follow. In immunocompromised patients, a progressive, life-threatening, disseminated form can occur. Following initial infection, hematogenous spread to the rest of the body, including the eye, can occur. A focal granulomatous choroiditis is thought to occur. This phase seldom is observed in humans.
In an experimental nonhuman primate model, inoculation of the organism via the carotid artery results in an active choroiditis. These foci are observed as discrete, round, yellowish choroidal lesions. Six weeks following inoculation of the organisms, isolating the organisms by any histologic techniques was not possible. The inflammatory response probably destroyed the invading organisms. With time, the lesions resolve, leaving the typical "punched-out" atrophic scars that disrupt the Bruch membrane (see Physical). Reexposure to the histoplasmin antigen may account for the enlargement of old scars and the emergence of new scars.
Visual loss in POHS is secondary to the development of CNV. Recently, pigment epithelium derived factor (PEDF) was found to have an inhibitory effect on ocular neovascularization. Another peptide, vascular endothelium growth factor (VEGF), is a well-known ocular angiogenic factor. The balance between antiangiogenic factors (eg, PEDF) and angiogenic factors (eg, VEGF) may determine the growth of CNV. This CNV usually grows in the subretinal space in a sheetlike fashion, not in the sub–retinal pigment epithelium (RPE) space. As the CNV grows, reactive hyperplastic RPE tries to surround and envelop the CNV. If successful, the CNV usually involutes.
Why CNV arises is unclear. Based on a case of a pregnant woman who developed a macular detachment during the third trimester, some propose that a type of vascular decompensation caused the CNV. A lymphocytic choroidal infiltrate usually is found near histo spots. Some hypothesize that an allergic reaction to Histoplasma antigens is an important stimulus for CNV growth. A few propose that the infectious granuloma secondary to the fungus is responsible for CNV growth. Others state that damage to the Bruch membrane by itself is a strong stimulus for CNV.
This condition occurs in endemic areas of the United States, including the Ohio and Mississippi River Valleys (Indiana, Ohio, Illinois, Kentucky, Tennessee, and Mississippi) and parts of the mid-Atlantic region (Maryland, West Virginia, and Virginia). Approximately, 200,000-500,000 new infections occur annually.
In an endemic area, 90% of patients with POHS had a positive histoplasmin skin test. In Maryland, 4% of those infected with histoplasmosis had POHS.
Peripheral atrophic scars were present in 2% of people living in endemic areas; disciform scars were found in 0.1% of people.
A clinical entity indistinguishable from POHS has been reported in a series of 10 patients from a nonendemic area, the Pacific Northwest. These patients tested negative to a lymphocyte stimulation assay with H capsulatum. Unlike series from the Midwest, all patients were female; 50% of them were myopic. The authors speculate that an atypical mycobacteria might be responsible for this entity.
H capsulatum is endemic in the Caribbean and Central and South America. No reports of POHS from these areas have appeared in the literature.
In the Netherlands and the United Kingdom, a clinical syndrome indistinguishable from POHS has been described. In the Dutch series by Suttorp-Schulten et al, a large number of female and myopic patients were reported.26 Given that H capsulatum is not found in Europe, some European colleagues have proposed to change the name from POHS to multifocal choroidopathy.
The cause of this condition is H capsulatum.
ARMD, Exudative
Toxoplasmosis
Birdshot chorioretinopathy
Punctate inner choroidopathy
Coccidioidomycosis
Multifocal choroiditis
Idiopathic choroidal neovascular membranes
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.
Antifungals, such as amphotericin B, are not helpful. Steroids anecdotally have been used in subfoveal CNV by a few observers.
Anecdotal, controversial evidence suggests efficacy in treating subfoveal CNV.
May decrease inflammation by reversing increased capillary permeability and suppressing PMN activity.
Gass recommends 40-100 mg qd for several wk, then alternate-day basis for several wk; if no response, rapidly taper and stop
Not established
Drugs, such as phenobarbital, phenytoin, and rifampin, induce hepatic enzymes and, therefore, increase clearance of corticosteroids; other drugs, such as ketoconazole, inhibit clearance of corticosteroids; adjust doses accordingly; corticosteroids have an unpredictable effect on anticoagulants, so monitor coagulation indices
Documented hypersensitivity; systemic fungal infections
C - Safety for use during pregnancy has not been established.
Secondary adrenocortical insufficiency may be induced; in periods of stress, an increased dosage is indicated; hold immunizations while the patient takes corticosteroids
Off-label use of triamcinolone.
Not established, but most vitreoretinal specialists inject 4-25 mg intravitreally
Not established
Coadministration with barbiturates, phenytoin, and rifampin decreases effects
Documented hypersensitivity; fungal, viral, and bacterial skin infections
C - Safety for use during pregnancy has not been established.
Use sterile technique when injecting triamcinolone into the vitreous cavity to avoid endophthalmitis; infectious and noninfectious endophthalmitis have been reported following intravitreal injection of triamcinolone; elevation of intraocular pressure has been reported to occur in up to 33% of eyes; retinal detachment may occur; long-term use may lead to progression of lens opacities
Reduction of leakage from abnormal, neovascular vessels, resulting in reduced visual loss.
A benzoporphyrin derivative monoacid (BPD-MA), consists of equally active isomers BPD-MAC and BPD-MAD, which can be activated by low-intensity, nonthermal light of 689-nm wavelength. After activation with light and in presence of oxygen, verteporfin forms cytotoxic oxygen free radicals and singlet oxygen. Singlet oxygen causes damage to biological structures within range of diffusion. This leads to local vascular occlusion, cell damage, and cell death. In plasma, verteporfin is transported primarily by low-density lipoproteins (LDL). Tumor and neovascular endothelial cells have increased specificity and uptake of verteporfin because of their high expression of LDL receptors. Effect can be enhanced by use of liposomal formulation.
6 mg/m2 (dissolved in 30 mL of solution) IV for 10 min
Second part of treatment consists of activation of drug: Recommended light intensity of 600 mW/cm2, takes 83 s to apply necessary light dose of 50 J/cm2
Not established
None reported; many drugs can influence effect; theoretical examples include concomitant use of other photosensitizer (eg, tetracycline, sulphonamide, phenothiazine, sulphonylurea, hypoglycemic substances, thiazide diuretics, griseofulvin) could increase photosensitivity; compounds that scavenge active oxygen species or radicals (eg, dimethylsulphoxide, beta-carotene, ethanol, formate, mannitol) could reduce activity; calcium channel blockers, polymyxin B, or radiation therapy can increase rate of uptake by vascular endothelium; anticoagulants, vasoconstrictors, or platelet-aggregation inhibitors (eg, thromboxane-A2 inhibitors) can reduce effectiveness
Documented hypersensitivity; porphyria
C - Safety for use during pregnancy has not been established.
Patients remain photosensitive to sunlight and strong artificial light for 48 h after infusion with verteporfin; wearing sunglasses and long-sleeved clothing highly recommended to avoid serious skin and eye burns; indoor lighting is safe in general and recommended over complete darkness because accelerates breakdown of active drug; caution in advanced liver disease; extravasation can cause severe pain, inflammation, swelling, and discoloration at injection site; cold compresses and analgesia help reduce pain and complications of extravasation
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POHS, ocular histoplasmosis, peripheral atrophic chorioretinal scars, peripapillary scarring, maculopathy, Histoplasma capsulatum, H capsulatum, histoplasmin skin testing, fungal infection, macular choroidal neovascularization, macular CNV, vision loss
Lihteh Wu, MD, Consulting Surgeon, Department of Ophthalmology, Vitreo-Retinal Section, Instituto De Cirugia Ocular, Costa Rica
Lihteh Wu, MD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Retina Specialists, Association for Research in Vision and Ophthalmology, and Pan-American Association of Ophthalmology
Disclosure: Nothing to disclose.
Teodoro Evans, MD, Retina Fellow, Vitreo-Retinal Section, Instituto De Cirugia Ocular, Costa Rica
Disclosure: Nothing to disclose.
Russell P Jayne, MD, Consulting Vitreoretinal Surgeon, The Retina Center at Las Vegas
Russell P Jayne, MD is a member of the following medical societies: American Medical Association, American Society of Cataract and Refractive Surgery, and American Society of Retina Specialists
Disclosure: Nothing to disclose.
Simon K Law, MD, PharmD, Assistant Professor of Ophthalmology, Jules Stein Eye Institute; Chief of Section of Ophthalmology Surgical Services, Department of Veterans Affairs Healthcare Center, West Los Angeles
Simon K Law, MD, PharmD is a member of the following medical societies: American Academy of Ophthalmology, American Glaucoma Society, and Association for Research in Vision and Ophthalmology
Disclosure: Nothing to disclose.
Steve Charles, MD, Director of Charles Retina Institute; Clinical Professor, Department of Ophthalmology, University of Tennessee College of Medicine
Steve Charles, MD is a member of the following medical societies: American Academy of Ophthalmology, American Society of Retina Specialists, Macula Society, and Retina Society
Disclosure: Alcon Laboratories Consulting fee Consulting
Lance L Brown, OD, MD, Ophthalmologist, Affiliated With Freeman Hospital and St John's Hospital, Regional Eye Center, Joplin, Missouri
Disclosure: Nothing to disclose.
Hampton Roy Sr, MD, Associate Clinical Professor, Department of Ophthalmology, University of Arkansas for Medical Sciences
Hampton Roy Sr, MD is a member of the following medical societies: American Academy of Ophthalmology, American College of Surgeons, and Pan-American Association of Ophthalmology
Disclosure: Nothing to disclose.
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