Pythium species can infect arteries in patients with risk factors for human pythiosis. Many clinicians are unfamiliar with the organism so misdiagnosis and delayed diagnosis are common.
Clinical and pathologic features:
(1) arteritis, often involving a large artery
(2) variable thrombosis with emboli
(3) ischemia distal to the lesion
(4) presence of thalassemia or other risk factor for human pythiosis
(5) a biopsy of the affected artery shows a necrotizing arteritis with hyphae seen on fungal stains.
(6) poor response to standard antifungal chemotherapy
The organism grows in standard fungal media, but false negative cultures may occur if a biopsy does not include viable organisms (which may only be present at the advancing edge of the infection).
In the past resection of infected vascular tissue was the only sure cure. Immunotherapy can be effective if the patient is stable enough.
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