Even seasoned dermatopathologists may be uneasy with the diagnosis of exotic worms and fungi like this.
Seattle - As more Americans travel abroad, they may return with exotic skin disease and fungi that dermatologists need to be ready to treat, says Dirk Elston, M.D., a member of the teaching staff in the departments of dermatology and pathology, Geisinger Medical Center, Danville, Pa. For example, consider the case of a 21-year old army reservist. Weeks after returning home from duty in Iraq, he notices a crawling sensation in his facial skin. The sensation slowly moves until it localizes on his forehead. A nodule becomes palpable at the site. The dermatologist performs an incisional biopsy and pulls a long worm from the wound.
According to Dr. Elston, even seasoned dermatopathologists may be uneasy with the diagnosis of exotic worms and fungi like this.
"But we'd better get familiar and comfortable with them," he says. "With worldwide travel becoming commonplace, physicians will be seeing more exotic diseases in the clinic. Although these infectious agents are uncommon, they are medically important. And other conditions like smallpox may be used as weapons of terrorism so the dermatologist and dermatopathologist must have the expertise to distinguish them from look-alikes such as barnyard pox," Dr. Elston tells Dermatology Times.
Dr. Elston reviewed the diagnostic histologic features of endemic and exotic helminthic, viral and fungal pathogens at the recent American Society of Dermatopathology meeting here.
To help educate physicians about these rare infectious agents, Dr. Elston focused on nine case studies. One agent, for instance, Rhinosporidium seeberi, causes rhinosporidiosis, which frequently presents as a polypoidal nasal lesion. Diagnosis is established on the morphological basis by the identification of 5- to 10-micron "endospores" and 50- to 1,000-micron sporangia. The endospores have been shown to comprise both lipid/protein nutritive bodies and other spherical bodies that are metabolizing units that reduce MTT (3-[4,5-dimethyl1-2thiazolyl]-2,5-diphenyl-2H tetrazolium bromide).
"This indicates the viability of these spherical bodies, provisionally identified as the electron-dense bodies that have also been shown to contain nucleic acids," Dr. Elston says.
Another infectious agent, dematiaceous fungi, are typically resistant to antifungals that would be used for aspergillosis. These fungi are a large and heterogenous group of molds that cause a wide range of diseases including phaeohyphomycosis, chromoblastomycosis and eumycotic mycetoma. Among the more important human pathogens are the Alternaria species, Bipolaris species, Cladophialophora bantiana and many others. These organisms are widespread in the environment and are found in soil, wood and decomposing plant debris. Cutaneous, subcutaneous and corneal infections with dematiaceous fungi occur worldwide, but are common in tropical and subtropical climates.
"As the melanin pigment may be inconspicuous in tissue," Dr. Elston explains, "we have to rely on other morphologic features to make the diagnosis. Many fungi, even dermatophytes, can stain fontana positive for melanin, so this is not a reliable feature. Unfortunately," he adds, "culture is slow, so the patient may die before culture results guide therapy. Morphologic diagnosis remains critical to patient care."
Newer tests, such as polymerase chain reaction (PCR), may prove to be valuable adjuncts, but currently many lack adequate sensitivity and specificity. Most forms of disease caused by dematiaceous fungi require both surgical and medical treatment. Itraconazole is currently the best documented antifungal agent for dematiaceous fungi.
Dr. Elston also discussed the pathogen sparganosis, a zoonosis that occurs occasionally in humans. Histologic features of this agent include tunnel formation lined by palisading histiocytes, and a worm with microvillus tegument overlying two thin layers of smooth muscle and a single row of tegumental cells. In humans, the infections can cause ocular, subcutaneous, central nervous system, auricular, pulmonary, intraosseous or intraperitoneal problems. Humans can become infected by ingesting infected copepods in drinking water or raw or undercooked amphibians, reptiles or mammals.
Other infectious agents