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Histoplasmosis
Histoplasmosis is caused by a fungus (Histoplasma
capsulatum) in the soil and is common in the central, mid-Atlantic and
southeastern states, particularly in the Ohio and Mississippi river
valleys. In these areas, up to 60 - 80% of the population may show a
positive histoplasmin skin test. The fungus is the result of certain
bird and bat "droppings" - particularly chickens. The fungus infects
people usually when the fungus is inhaled when dust is stirred-up; for
example, when cleaning a chicken coop. Young infants, people with lung
problems and a history of smoking, and immunocompromised patients are at
particular risk for disseminated (wide-spread) histoplasmosis.
Although the majority of people in
highly infected areas have been exposed to histoplasmosis, most have no
or very mild symptoms. Because it is difficult to confirm that a person
is having vision problems related to histoplasmosis infection, such
people are usually referred to as having POHS - "presumed ocular
histoplasmosis syndrome." POHS occurs in people without active
histoplasmosis and ophthalmologic signs include a macular subretinal
neovascular membrane that may or may not have bleed, scattered choroidal
lesions that appear punched-out and yellowish, and peripapillary
choroidal atrophy. Importantly, people with POHS do not have
inflammatory cells in the vitreous. The patient may experience a loss
of visual acuity in one or both eyes, distorted vision, blurred vision
or/and blind spots in the visual field. Often the eye doctor will
follow a patient with the Amsler grid - a piece of paper that has a grid
of horizontal and vertical lines with a fixation dot in the middle. The
Amsler grid is ideal for detecting blind spots in or near central vision
as well as spatial distortions.
It is important to note that the
majority of people that have become infected with histoplasmosis, when
the infection was with a small amount of fungus, do not yield any lung
changes on x-ray. Sometimes only small infiltrates or hilar adenopathy
are found on x-ray. In addition pre existing lung problems,
particularly in smokers, may mask or cover-up lung changes due to the
histoplasmosis infection. As a consequence, it is not surprising that
patients with POHS do not always exhibit positive x-ray findings. Some
believe that POHS may be the result of a "benign systemic histoplasma
infection" and that years later POHS develops.
Treatment for POHS depends on numerous
factors. Laser photocoagulation for subretinal neovascular membranes
has been found to reduce visual acuity loss and offer shot-term
protection. POHS may flare-up from time to time and the reason for the
flare-ups is not known; are these reinfections or simply reactivation of
a dormant fungus? It does appear, however, that attacks of POHS and
macular deterioration with loss of central vision appear related to
stressful events in the patient's life. Some suggest that a well
balanced diet and supplemental vitamins may improve a person's
resistance to the fungus and decrease reinfections or additional
flare-ups of the disease. It is also recommended that to avoid or
reduce the chance of bleeding of macular or paramacular lesions that one
avoid elevations above 7000 feet (sorry, no mountain climbing or skiing
in high altitudes) and avoid aspirin. |
