Page 188 - The Netter Collection of Medical Illustrations - Integumentary System_ Volume 4 ( PDFDrive )

Plate 6-13 Integumentary System

Ulcerating plaque of tongue
HISTOPLASMOSIS due to histoplasmosis. Lesion
may be identical in appearance
to carcinoma of tongue.
Histoplasmosis is endemic in the Ohio River Valley but
exists throughout North America and is also seen in
Central and South America. It is a primary pulmonary
disease, with the skin being secondarily involved in dis-
seminated disease; however, isolated cutaneous disease
can result from direct inoculation. The disease is typi-
cally seen in immunocompromised patients. Patients
typically breathe in the infective spores, which lodge in
the pulmonary tree. Most infections are subclinical.
Clinical Findings: The disease is seen primarily in
immunocompromised patients. Other risk factors
include occupations that increase the patient’s contact
with bat or bird droppings in an endemic region.
The fungus is not found within bird droppings, but
the droppings provide the perfect environment for the
fungus to grow and reproduce. Patients inhale the
spores into the lungs. Most have no symptoms. Some
have mild flu-like symptoms that go undiagnosed or
misdiagnosed as an upper respiratory infection. The
primary infection heals, and the lungs may have visible
findings on chest radiography. Variable radiographic
findings are seen. Small, symmetrically located areas of
hilar miliary calcification are the most common finding.
Other lung findings can mimic those of tuberculosis,
lung cancer, or metastatic cancer. Bilateral hilar ade-
nopathy may be seen, as may lobar pneumonia.
Dissemination of the disease to other organs can Mycelial or free-living phase of H. capsulatum as it
occur in the immunocompromised host. The skin is exists in nature or in culture
commonly affected in disseminated disease. The skin
findings often appear as papules, plaques, or nodules
with varying degrees of ulceration. Subcutaneous
abscess formation may occur, and fistulas and sinus tract Spores of mycelial phase of
formation may be prominent. Surrounding redness may H. capsulatum. Inhalation of these
give the appearance of cellulitis. Adenopathy in the is the source of infection.
draining lymph nodes is commonly appreciated. The
diagnosis is dependent on the histological findings and
the culture results.
Histology: Skin biopsy specimens show pseudocarci-
nomatous hyperplasia of the epidermis with an underly-
ing granulomatous infiltrate. Ulceration and abscess
formation are not uncommon with widespread necrosis.
The yeast-like organisms can be appreciated in the
cytoplasm of histiocytes. This is one of the few infec-
tions in which one sees phagocytized histiocytes. The
yeast structures are round to oval, and there may be a
clear region surrounding the yeast cell. Yeast organisms
are also appreciated within the dermis, between and
within the inflammatory infiltrate. They can be high-
lighted by use of special histology stains such as the
periodic acid–Schiff stain or the Grocott silver stain.
The fungus is best cultured on Sabouraud’s media.
The fungus in its mycelial phase grows slowly. It appears Dimorphic fungus. H. capsulatum in tissue H. capsulatum in a macrophage, termed
as a brown, fluffy fungus on culture. a phagocytized histiocyte. In this yeast or
Pathogenesis: Histoplasma capsulatum is a dimorphic tissue phase, the organism is not
fungus that is responsible for a wide range of infections transmissible from person to person.
including pulmonary, pericardial, and cutaneous dis-
eases. The fungus is ubiquitous in nature and is found
in soil, where it lives as a saprophyte. Spores from the
mycelial phase of the fungus are inhaled or inoculated preexposed or newly exposed patient becomes immu- immunocompromised should be started on therapy
directly into the skin. Once they have entered the body, nosuppressed, the patient is at risk for disease reactiva- with one of the three most efficacious and best-studied
the change in temperature causes transformation of the tion and serious sequelae. medications: fluconazole, itraconazole, or amphotericin
spores into the yeast form of H. capsulatum. Most infec- Treatment: Most cases of primary pulmonary disease B. Treatment may be prolonged. Patients who are
tions go unnoticed, and most of the others induce a go undiagnosed, and the patient’s immune system con- found to have the acquired immunodeficiency syn-
subclinical scenario or a mild, flu-like illness. Most tains the fungus. In those patients with mild pulmonary drome benefit from directed therapy against the human
cases are self-contained, and the only evidence of symptoms who are not immunocompromised, therapies immunodeficiency virus. Patients taking chronic immu-
disease is the formation of granulomas within the lungs can be withheld, because most cases resolve spon- nosuppressants should have their medications discon-
and a positive skin delayed-hypersensitivity test. If a taneously. Patients who have more severe disease or are tinued or decreased, if possible.

174 THE NETTER COLLECTION OF MEDICAL ILLUSTRATIONS