Orbital pythiosis: a non-fungal disease mimicking orbital mycotic infections, with a retrospective review of the literature

In the past decade there have been four well-documented cases of orbital pythiosis caused by Pythium insidiosum. All were recorded in apparently healthy children. Although pythiosis seems to be a rare infection in humans, we recently conducted a review of the medical literature to investigate misdiagnosed cases of orbital pythiosis in the past 100 years in children. To track putative cases of orbital pythiosis, we first identified orbital cases initially diagnosed as fungal infections. We were particularly interested in cases (a) involving apparently young healthy hosts, (b) the presence of hyaline, aseptate hyphal elements in the infected tissues, (c) the morphological features of the hyphal elements, (d) the presence of an eosinophilic granulomatous reaction with the Splendore-Hoeppli phenomenon around the mycelial elements, (e) resistance to antifungal therapy, (f) outcome after therapy, if any, and (g) cultural strategies. This study showed that indeed, there had been five other recorded cases of orbital infections, all in young children in the USA, with characteristics consistent with infections caused by P. insidiosum. The reports had described those cases of orbital-cranial-arterial diseases as patients with aspergillosis (one case), penicilliosis infection (one case), and zygomycosis (three cases). We reviewed those anomalous cases and discuss details about their clinical, pathologic, therapeutic, and etiologic evidence used to reclassify them as putative cases of orbital pythiosis.