Infectious Optic Neuritis
Bacterial, viral, or fungal infections of the optic nerve can occur because of spread of infection from adjacent anatomical structures or as part of a systemic infection, particularly in immunocompromised patients. Bartonella henselae, Treponema pallidum, and Mycobacterium tuberculosis are the organisms most often responsible for primary bacterial infections of the optic nerve. Examples of infectious diseases caused by viruses include herpes simplex (due to infection with human herpesvirus 1 or 2) and varicella (due to varicella-zoster virus infection). Acute disseminated encephalomyelitis (ADEM) is an immune-mediated demyelinating disease that often follows bacterial or viral infection. Histiocytes and microglia remove the damaged myelin, and astrocytic proliferation ultimately produces a glial scar, or plaque.
Fungal infections that can involve the optic nerve include mucormycosis, cryptococcosis, and coccidioidomycosis. Mucormycosis (also called zygomycosis) generally results from direct extension from nearby structures, usually a contiguous sinus infection. Cryptococcosis generally begins as a pulmonary infection, which can disseminate to the brain. Optic nerve involvement generally occurs via direct spread from the intracranial cavity and is commonly associated with multiple foci of necrosis with little inflammatory reaction (Fig 15-4). Coccidioidomycosis also begins as a primary pulmonary infection and can disseminate to other areas of the body, including the optic nerve and eye, producing necrotizing granulomas. Infectious optic neuritis is discussed further in BCSC Section 5, Neuro-Ophthalmology.
Figure 15-4 Cryptococcosis of the optic nerve in an immunocompromised patient. The dura is infiltrated by cryptococcal organisms (arrows). This yeast has a mucopolysaccharide capsule that stains red with mucicarmine stain. No inflammatory infiltrate is observed.
(Courtesy of Tatyana Milman, MD.)
Excerpted from BCSC 2020-2021 series: Section 4 - Ophthalmic Pathology and Intraocular Tumors. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.