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PARACOCCIDIOIDOMYCOSIS

PARACOCCIDIOIDOMYCOSIS

Paracoccidioidomycosis, also known as South American blastomycosis, is a disease that is seen almost exclusively in regions of Central and South America. It is caused by the dimorphic fungus, Paracoccidioides brasiliensis. Most infections are acquired by direct inhalation of the chlamydospores. The fungus is found in the environment in the mycelial or mold phase; it converts to the yeast phase at body temperature. Brazil has the highest incidence of paracoccidioidomycosis. Primary lung infection may lead to disseminated disease, with the skin being secondarily infected. Direct inoculation into the skin causes primary cutaneous disease.

Clinical Findings: This fungal infection is more common in men than in women, for reasons poorly understood. It may be that men are more likely to have occupational exposures (most commonly, farming). A protective effect of estrogen also has been hypothesized. There is no race predilection. Immunocompetent hosts who are exposed to the fungus are likely to develop a subclinical infection. Then, either the fungus becomes walled off in the form of granulomas within the lung or the patient goes on to develop clinical disease. Serological testing may show evidence of past exposure in healthy subjects with no clinical findings. Some hosts have a constellation of flu-like symptoms that include malaise, weight loss, fatigue, fever, pneumonitis, and pleurisy. Progressive pulmonary lesions may occur regardless of immune status, but they are more severe in patients who are immunosuppressed.

PARACOCCIDIOIDOMYCOSIS
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Bilateral pulmonary infiltrates are seen on chest radiography and are similar to the radiographic findings of tuberculosis. The infiltrates often form consolidated areas with cavitations that heal with emphysematous changes. Almost all cases of paracoccidioidomycosis affect the lung. Once established, the fungus is able to disseminate to the skin, draining lymph nodes, adrenal glands, central nervous system, peritoneum, and gastro-intestinal tract.

Skin lesions in paracoccidioidomycosis come in two distinct varieties. Disseminated disease is the more frequently encountered subtype. The lesions are predominantly on the head and neck, especially around the oral and nasal passages. The oral mucosal membranes and tongue are involved. Nasal and pharyngeal ulcerations are so frequently encountered that they have been given a name, Aguiar-Pupo stomatitis. The mucosal lesions are often peppered with pinpoint hemorrhagic areas. The skin findings may include papules, nodules, or fungating plaques. Ulceration is almost universal, and patients complain of pain and swelling. Cervical lymph nodes are enlarged. The infected lymph nodes often form sinus tracts to the skin and drain spontaneously.

The second form of cutaneous paracoccidioidomycosis is caused by direct inoculation of the fungus. The fungal elements are normally found in the soil, and piercing of the skin with a contaminated object can lead to primary cutaneous paracoccidioidomycosis. These lesions appear as papules or draining tender nodules with or without overlying ulceration. Some may spontaneously resolve, but most slowly enlarge.

Histology: Skin biopsy specimens show pseudocarcinomatous hyperplasia of the epidermis with varying degrees of ulceration and abscess formation. There is a mixed inflammatory infiltrate. Suppurative granulomatous inflammation is seen within the underlying dermis. The fungus can be seen on routine hematoxylin and eosin staining with close inspection. The cells of the yeast phase are thick walled and refractile. They can be seen in the shape of a “mariner’s wheel,” which is highly characteristic and specific for P. brasiliensis. The fungus can be highlighted with a multitude of special staining methods, including periodic acid–Schiff and sliver stains. The fungus is easily cultured on Sabouraud’s medium and shows fluffy white colonies.

Pathogenesis: The fungus P. brasiliensis has unusual living requirements, and its growth in the environment is dependent on the soil pH, the altitude, and a consistent temperature. Alterations in the optimal growing conditions decrease the survivability of the organism. The host response to this fungus depends on an intact Th1 helper T-cell response.

Treatment: Treatment with itraconazole has had great success and has drastically altered the prognosis of this disease. As with all systemic fungal infections, treatment courses last for months to a year. Historically, sulfonamides were used. If left untreated, this disease has a significant mortality rate. Ketoconazole and fluconazole have also been used successfully, and amphotericin B is now reserved for the most severe cases and for those that fail to respond to azole or sulfonamide therapy.