Causes of Optic Neuritis Other than Primary Demyelination

Parainfectious optic neuritis typically follows the onset of a viral or, less often, a bacterial infection by 1 to 3 weeks (37,434,435). It is more common in children than in adults and is thought to occur on an immunologic basis, producing demyelination of the optic nerve. The optic neuritis may be unilateral, but it is often bilateral. The optic discs may appear normal or swollen. Swelling of the peripapillary retina may be observed in patients with anterior optic neuritis. If a star figure composed of lipid exudates develops in the macula of the affected eye, the condition is called ‘‘neuroretinitis’’ (discussed later). If there is evidence of optic disc swelling but no evidence of optic nerve dysfunction, and the intracranial pressure is normal, the inflammation is assumed to be affecting the periphery of the nerve and is called ‘‘perioptic neuritis’’ or ‘‘optic perineuritis’’ (discussed later). Parainfectious optic neuritis, whether viral or bacterial, may occur in patients with no evidence of neurologic dysfunction or in association with a meningitis, meningoencephalitis, or encephalomyelitis. When neurologic manifestations are present, patients have typical abnormalities in the CSF. Patients with encephalitis usually have disturbances on electroencephalography and also may have changes in the brain seen by neuroimaging, whereas patients with encephalomyelitis may show such changes in both the brain and the spinal cord. Visual recovery following parainfectious optic neuritis is usually excellent without treatment. Whether corticosteroids hasten recovery in patients with postviral optic neuritis is unknown, but this treatment is reasonable to consider, particularly if visual loss is bilateral and severe. Optic neuritis may occur in association with infections by a large number of both DNA and RNA viruses, including adenovirus (436,437), Coxsackie virus (438,439), cytomegalovirus (440), hepatitis A (441), hepatitis B (442,443), human herpesvirus type 4 (Epstein-Barr virus) (444–448), human immunodeficiency virus (HIV) type 1 (449,450), measles (451–455), mumps (456–458), rubeola, rubella (459), and varicella zoster (in chicken pox [460,461] and in herpes zoster [462,463]). The neuro-ophthalmologic significance of these and other viruses is discussed in detail in Chapters 57 and 58. Bacterial infections can produce optic neuritis. Some bacterial infections in which anterior or retrobulbar optic neuritis may occur include anthrax (464), -hemolytic streptococcal infection (465), brucellosis (466,467), cat scratch disease (39,468,469,470), meningococcal infection (471), pertussis (472), tuberculosis (473–477), typhoid fever (478,479), and Whipple’s disease (480). The neuro-ophthalmologic significance of these and other bacteria is discussed in detail in Chapter 49.