Zygomycosis (also known as phycomycosis or mucormycosis) is the most common and the most virulent fungal disease involving the orbit. The specific fungal genus involved is usually Mucor or Rhizopus. These fungi, belonging to the class Zygomycetes, almost always extend into the orbit from an adjacent sinus or the nasal cavity. The fungi invade blood vessel walls, producing thrombosing vasculitis. The resultant tissue necrosis promotes further fungal invasion.
Patients commonly present with proptosis and an orbital apex syndrome (internal and external ophthalmoplegia, ptosis, decreased corneal sensation, and decreased vision). Ascending infection may result in cavernous sinus thrombosis (Fig 4-5). Because of the thrombosing vasculitis, the infection may not produce significant orbital inflammation and an unusually white and quiet eye should prompt concern for orbital ischemia.
Predisposing factors include systemic disease with associated metabolic acidosis, diabetes mellitus, malignancies, and treatment with antimetabolites or steroids. Biopsy of the necrotic-appearing tissues in the nasopharynx, involved sinus, or orbit confirms the diagnosis and shows nonseptate, large branching hyphae that stain with hematoxylin-eosin, unlike most fungi (see the discussion of zygomycosis in BCSC Section 5, Neuro-Ophthalmology).
Figure 4-5 Right-sided sino-orbital zygomycosis in a patient with diabetic ketoacidosis. A, In this photograph, complete right upper eyelid ptosis and ophthalmoplegia are present in the patient. B, Wide surgical debridement consisting of orbital exenteration and sinus surgery was life-saving. CT (C) and MRI (D) axial scans show orbital and sinus involvement as well as cavernous sinus thrombosis (arrow).
(Courtesy of Bobby S. Korn, MD, PhD.)
Treatment should include a multidisciplinary team to address any underlying predisposing disease, perform wide surgical debridement, and administer antifungal therapy. Diabetic ketoacidosis, in particular, requires prompt correction; this condition produces more free serum iron, thought to be central for fungal pathogenesis. Antifungal therapy may consist of IV or liposomal amphotericin B; posaconazole or voriconazole may be used in patients who cannot tolerate the adverse effects of amphotericin. In addition, retrobulbar injection of amphotericin B may be considered. Adjunctive treatments include hyperbaric oxygen therapy. Despite aggressive surgical debridement, including exenteration, the prognosis for survival remains poor and often depends on whether the underlying systemic predisposing disease is immediately treatable.
Excerpted from BCSC 2020-2021 series: Section 10 - Glaucoma. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.