Laboratory Studies
Diagnosis is typically made by identification of fly larvae or maggots. The exact type of species can be difficult to determine from examination. [5] However, CBC count may show leukocytosis and eosinophilia.
Imaging Studies
MRI has been used in a number of cases of cerebral myiasis; breast myiasis; and facial, orbital, and furuncular myiasis. Ultrasonography can also be very useful in establishing the diagnosis and in determining the size of the larvae. CT scan has also been suggested. [15]
In one study, Doppler ultrasonography (DUSG) was performed using a high-resolution (10-MHz) soft-tissue transducer. Using the standard mode, hypoechogenic masses underneath the skin were first located, and then DUSG was used, which demonstrated circulation of fluid within the parasite as well as the number of parasites, their size, and their situation within the lesion. This is especially useful when lesions are still small and look like insect bites. Secretion and pain are minimal or absent, and the punctum is almost always absent. In these cases, high-resolution DUSG proved to be 100% effective in diagnosis. [16]
Procedures
Biopsies are not necessary, but if performed, histopathologic findings include an ulcerated epidermis with an inflammatory infiltrate of neutrophils, lymphocytes, giant cells, mast cells, plasma cells, and eosinophils that occur in stages. The larvae can be seen in cross-section. [1, 16]
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Mature larva of the Dermatobia hominis fly; rows of hooks apparent on its tapered body. Image courtesy of Kenneth E Greer.
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Boil-like lesion on toe of a patient with botfly myiasis; the central punctum is apparent. Image courtesy of Kenneth E Greer.
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Boil-like lesions on a patient with botfly myiasis; the central punctum is apparent. Image courtesy of Kenneth E Greer.
