Overview of Ocular Histoplasmosis Syndrome (OHS)

Overview of Ocular Histoplasmosis Syndrome (OHS)Dr Pradeep VenkateshHistoplasmosisAmol D Kulkarni and Suresh R ChandraIntroductionHistoplasmosis is a systemic disease caused by Histoplasma capsulatum.1IntroductionHistoplasmosis is a systemic disease caused by Histoplasma capsulatum.1 It produces intracellular granulomatous inflammation of many organs including eyes, lungs, liver, spleen, etc. Ocular histoplasmosis syndrome (OHS) is characterized by a triad of signs of punched-out atrophic choroidal scars in the macula or periphery, peripapillary atrophy and choroidal neovascular membrane (CNVM).2Etiology-AetiologyHistoplasmacapsulatumH. capsulatum, a dimorphic fungus, is presumed to play a causative role in the development of OHS.1 There argon few reports of pathologic and molecular express supporting a the direct role for of H. capsulatum in the development of chorioretinal scars, however, no serologic confirmation of histoplasmosis infection has been reported.3,4 A haematogeno us dissemination of the fungus results in choroidal invasion and sequent scarring. Additionally, disseminated histoplasmosis presents with intraretinal infiltrates composed of histoplasma yeast cells that are easily demonstrable on histology. Extensive study of the affected individuals in Europe and the United States has revealed the presence of human leukocyte antigen (HLA)-DR15). 1 Please provide the full form of DR.5 No full form it indicates type of HLAThis HLA association suggests that immune reaction is likely to play a major(ip) role during the development of scarring and CNVM. H. capsulatum may induced localized autoimmune reaction in the retina. However, an infection with this fungus is not an absolute requirement for the development of clinical OHS. Because of this insufficiency of association, in that location has been a suggestion to rename this clinical syndrome as multifocal choroidopathy.EpidemiologyOHS is most common in the Ohio and Mississippi River valleys of th e United States, which are endemic for H. capsulatum.6 Up to 70% of the population living in the endemic areas reacts positively to the histoplasmin skin testing and 1.5% exhibits the distinctive fundus findings. 7It can be a blinding disease in its more(prenominal) severe manifestations. There is no gender predilection, although some reports show a higher prevalence in women.PathobiologyOHS belongs to the spectrum of autoimmune diseases triggered by an infectious organism, with H. capsulatum being unrivaled of several candidate pathogens. It is characterized by a chronic reaction to the immunogenic residua of the H. capsulatum, which acts as a nidus for inflammation. Light microscopy reveals mixed inflammatory cells in the choroidal lesions with the loss of superimposed retinal pigment epithelium. There are adhesions between the outer retina and choroidal lesions. The genesis of CNVM in OHS is thought to be caused by the disruption of Bruchs membrane at the site of atrophic scar .Systemic FeaturesfeaturesMycilia Mycelia of Histoplasmosishistoplasmoses are inhaled and they transform to the yeast form shortly and infect lungs. They can produce caseation and enlargement of hilar nodes, which produce typical shadows on X-ray. About 90% of cases are benign and do not produce symptoms. In dDisseminated2 Kindly OK histoplasmosis are is characterized by pyrexia, vomiting and enlargement of liver, spleen, and lymph glands. The link involvement of skin, mouth, gastrointestinal tract and heart may also occur.Ocular FeaturesfeaturesThe clinical findings in OHS include peripapillary atrophy, multiple punched punchedout white atrophic choroidal scars (histo spots), and a macular CNVM, attach to by the complete absence of a cellular reaction in the anterior chamber or vitreous cavity (Fig. 40.1(aA).6 The histo spots are considered to be the earliest stage of the disease, and are usually asymptomatic (Fig. 40.1 (Bb). CNVM will develop in fewer than 5% of individuals with histo spots. The Clinical clinical presentation of CNVM involves acute or insidious onset of painless progressive blurring of central vision and metamorphopsia. The Fundus fundus examination typically shows a yellow-green subretinal discolouration with accumulation of subretinal fluid. In advanced cases, there is subretinal fibrosis leading to disciform scar formation and that is associated with severe central visual loss. 9The exact time frame between the initial choroidal scarring and CNVAQ3 Please check if CNV stands for choroidal neovascularizationand CNVM is choroidal neovascular membrane and should be replaced with CNVMNO development is difficult to determine given that histo spots are asymptomatic. New histo spots may develop in more than 20% of individuals eyepatch they are under observation, however, only 3.8% progress to CNV. The precipitating factors promoting such progression are not known. Some studies implicate emotional stress and tension headaches as associated ev ents.DiagnosisOHS is a clinical diagnosis and relies on the observation of characteristic fundus lesions in one or both eyes. Intravenous fluorescein angiography (FA) and optical viscidity tomography (OCT) can assist in the evaluation of CNVM (Figs. 40.2 and 40.3). FA assists in identifying areas of CNVM and in planning photodynamic therapy. OCT is a useful tool for the detection and monitoring of treatment response.10TreatmentThe optimum treatment of subfoveal and juxtafoveal CNVM is the main focus in OHS. Histo spots are asymptomatic in most cases and require no treatment until a progression of the disease is detected.9-11Corticosteroids Regimens of systemic corticosteroid therapy were widely used in early studies of ocular histoplasmosis. 12Few clinical studies have evaluated the role of subtenons and intraocular triamcinolone. The intravitreal steroids demonstrated flourishing visual outcomes however, they are associated with cataract formation or progression and increased int raocular pressure.13Laser photocoagulation Laser Photocoagulation photocoagulation effectively inhibits the progression of OHS-related CNV. In randomized trials, the Macular Photocoagulation Study demonstrated that argon and krypton laser photocoagulation is effective in treating swell up-defined, classic extrafoveal, juxtafoveal, and peripapillary CNV lesions secondary to OHS.14, 15 Only 12% of treated individuals experienced significant disease progression, compared with 42% of the soften patients.Surgical therapyThe role of submacular surgery for the removal of CNV lesions was evaluated in a multicentere randomized clinical trial. 16The study data indicate that surgery may be salutary to patients with visual acuity worse than 20/100, and subfoveal CNV.Photodynamic therapy Verteporfin in Ocular Histoplasmosis study enrolled 26 patients prospectively with subfoveal CNV and demonstrated an improvement of visual acuity from baseline as well as an absence of serious adverse events at in 2 years.17Anti-vascular endothelial growth factor (VEGF) therapy Several intravitreal anti-vascular endothelial growth factor (VEGF) treatments are currently being pursued for the treatment of OHS-related CNV. Few retrospective studies have evaluated the role of intravitreal anti-VEGF therapy for CNV associated with OHS. One such study by Ehrlich et al. found that at least 50% of eyes with subfoveal or juxtafoveal CNV experienced =3 three lines of vision gain and 91.5% to 100% of patients had improved or had stable visual acuity (at 3- to 12-month follow-up) after the intravitreal bevacizumab therapy. 18Similarly, the results concerning the therapeutic efficacy of ranibizumab are promising. Both treat-and-extend and pro re nata treatment strategies were effective. A study by Nielsen et al. demonstrated that many eyes require long-run anti-VEGF therapy to suppress the choroidal neovascular activity in OHS.19Suggested readingSmith RE, Ganley JP. An epidemiologic study of presum ed ocular histoplasmosis. Trans Am Acad Ophthalmol Otolaryngol 1971 75994-1005.Gass JDM, Wilkinson CP. Follow-up study of presumed ocular histoplasmosis. Trans Am Acad Ophthalmol Otolaryngol 1972 76672694.Hawkins BS, Alexander J, Schachat AP. Ocular histoplasmosis. In Retina. Ryan, SJ, Schahchat, AP, editors. Retina. St. Louis, MO , Mosby 20014 Please check the author spelling.Oliver A, Ciulla TA, Comer GM. New and classic insights into presumed ocular histoplasmosis syndrome and its treatment. Curr Opin Ophthalmol. 2005 Jun16(3)160165.Prasad AG, Van Gelder RN. Presumed ocular histoplasmosis syndrome. Curr Opin Ophthalmol. 2005 dec16(6)364368.Macular Photocoagulation Study Group. Argon laser photocoagulation for ocular histoplasmosis results of a randomized trial. Arch Ophthalmol 1983 10113471357.Macular Photocoagulation Study Group. Krypton laser photocoagulation for neovascular lesions of ocular histoplasmosis results of a randomized clinical trial. Arch Ophthalmol 1987 1051499-1 507.Rosenfeld PJ, Saperstein DA, Bressler NM, et al. Photodynamic therapy with verteporfin in ocular histoplasmosis uncontrolled, open-label 2-year study. Ophthalmology 2004 11117251733.Nielsen JS, Fick TA, Saggau DD, Barnes CH. Intravitreal anti-vascular endothelial growth factor therapy for choroidal neovascularization secondary to ocular histoplasmosis syndrome. Retina. 2012 Mar32(3)468472.Fig. ure 40.1 Fundus photographs of a patient with OHS showing peri-papillary atrophy and CNV with subretinal haemorrhage in the right eye (A) and macular histo spot in the left eye (B).Choroidal neovascularizationFig. ure 40.2 Early (A) and late (B) phase fluorescein photographs showing CNV with subretinal haemorrhage secondary to OHS.Fig. ure 40.3 OCT stare showing CNV with intraretinal fluid secondary to OHS.