|Year : 1980 | Volume
| Issue : 1 | Page : 9-11
Histoplasmin skin sensitivity
RPS Bhatia, KS Mehra, AK Tewari
Department of Ophthalmology Institute of Medical Sciences Banaras Hindu University, Varanasi, India
3-Gurudham Durgakund Road Varanasi-221005
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Bhatia R, Mehra K S, Tewari A K. Histoplasmin skin sensitivity. Indian J Ophthalmol 1980;28:9-11
The association of ocular histoplasmosis with systemic histoplosmosis is tenuous. An etiological relationship between H. capsulatum and the characteristic clinical entity of presumed 'ocular histoplasmosis syndrome' is by no means established.
In one study of the 800 cases of presumed histoplasmic choroiditis none had symptomatic systemic (extra ocular) histoplasmosis; similarly no case of proved active systemic histoplasmosis was seen developing into histoplasma uveitis. In another study conducted in the United Kingdom none of the patients, having the typical clinical entity of the presumed ocular histoplasmosis syndrome, had any evidence of infection with H. capsulatum. On the other hand this syndrome was not found in one study of a community with endemic H. capsulatum infection.
A geographical study had shown that histoplasmic choroiditis, is seen in areas where positive skin test to histoplasmin are seen. Van Metre and Maumenee (1964) in an epidemiologic study have found a statistically significant relationship between positive histoplasmin skin test and the specific clinical entity described as presumed ocular histoplasmosis. Other epidemiologic studies,,; have also provided some evidence for an association between the histoplasmic ocular syndrome and the previous exposure to H. capsulatum.
On reviewing the literature it becomes obvious that the clinical entity which forms the syndrome of presumed ocular histoplasmosis has not yet been proved to be caused by H. capsulatum. The present work was undertaken to find out an association between uveitis and previous exposure to H. capsulatum as shown by the histoplasmin skin testing and to establish the incidence of positive reactors to histoplasmin in normal population having no uveitis or symptomatic systemic histoplasmosis in this part of India where no such study has been conducted in past. An attempt has also been made to correlate between type of uveitis on the basis of segment involvement and the histoplasmin skin sensitivity.
| Material and method|| |
The present study was carried out in the Department of Ophthalmology of the Institute of Medical Sciences, Banaras Hindu University. The study included 70 cases of clinical uveitis of which 47 patients had iridocyclitis, 16 patients had posterior uveitis and the rest 7 patients belonged to panuveitis group. The control group consisted of those 118 persons who came to our department for some sort of refractory errors.
None of the individuals from control group or study group had have any evidence of systemic histoplasmosis clinically. Moreover, the control group was selected after thoroughly investigating clinically to exclude any type of eye involvement other than refractory errors. No age and sex bar was followed.
Histoplasmin H-49 was used as antigen to carry out skin testing. 0.1 ml of 1 : 1000 dilution was injected intracutaneously on the flexor surface of the left forearm and reading was done 2 days later. 2 mm or more of induration was taken as a positive response to histoplasmin.
| Observations|| |
Among the cases of uveitis a total of 7.14% were the positive reactors. As compared to it 6.78% of the controls showed positive reaction with the skin testing to histoplasmin. The details are given in the [Table - 1].
| Discussion|| |
Study of patients with history of acute or chronic systemic histoplasmosis have failed to reveal any ocular changes suggestive of presumed ocular histoplasmosis over those that are to be expected in a control group; viceversa also holds true. More than 99% of the people who have a positive histoplasmin skin test, acquire it through the benign asymptomatic type of histoplasmosis. At times this histoplasma infection may be mild enough to escape notice. Cases of ocular histoplasmosis have been found apparently coming from this benign group.
Histoplasmin skin test is specific for H. capsualtum infection with cross reaction only to blastomycin in stronger dilutions. Histoplasmin sensitivity corresponds well with the presence of systemic histoplasmosisis,. In cases of ocular disease in one study it has been found negative in 11% cases of clinically typical histoplasmic choroiditis. False negative responses must be kept in mind, which are common specially in older people. Skin test studies have indicated rapid conversion to positivity during childhood in areas endemic for H. capsulatum.
6.78% positive reactors in normal population suggest the fact that benign asymptomatic histoplasma infection is of frequent occurrance as compared to symptomatic systemic histoplasmosis. As almost similar percentage of positive reactors were found in uveitis cases, it can be concluded that it is difficult to diagnose a case as histoplasma uveitis on the basis of a positive histoplasmin sensitivity in uveitis cases. It is possible that uveitis in such cases might have some other etiology and histoplasmin senstivity is only coincidental as a result of benign asymptomatic systemic histoplasmosis. In this regard it must be remembered that 99% systemic infection with H. capsultum are benign having no symptoms and such cases almost always show a positive skin test to histoplasmin. So a positive response to histoplasmin in uveitis cases should not be given much emphasis over those that are to be expected in a control group.
The occurrence of a positive reactor in iridocyclitis group of our series of study appears just coincidental with the benign systemic histoplasmosis in this patient. It should not be given much significance. On the other hand, association of positive reactors with postertor uveitis was 25%. This high percentage can be attributed to H. capsulatum. On excluding nearly 7% incidence of benign asymptomatic systemic histoplasmosis, on the basis of positive reactors in normal population, an indirect conclusion can be made which reveals that in about 18% case of posterior uveitis H. capsulatum is an etiological agent in this part of India.
The factors affecting the sensitivity of ocular tissue to H. capsulatum are yet to be found, Physical and emotional stresses have been found associated with exacerbation of ocular histoplasmosis. Factors for the initiation of ocular histoplasmosis have not been worked out.
| Summary and conclusion|| |
This study was done to establish the incinence of positive reactors to histoplasminskin test in uveitis cases and in normal persons. It was observed that the control group showed an incidence of 6.78% of positive reactors while in uveitis patients the incidence was 7.14%. The value of this test in relation to the segment involved in uveitis and the histoplasmin skin sensitivity has been discussed.
| References|| |
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[Table - 1]