Figure 14-19 Axial FLAIR MRI scan showing bilateral temporal lobe signal abnormalities in a patient with herpes

encephalitis. (Courtesy of Joel Curé, MD.)

Mycobacterium

Mycobacterium tuberculosis and Mycobacterium avium-intracellulare complex can infect the brain

and eye. The neuro-ophthalmic manifestations of tuberculous meningitis include photophobia, third and sixth nerve paresis, papilledema, retrobulbar optic neuritis, and anisocoria. Cerebral infarction can result from obliterative endarteritis. Neuroimaging studies may show hydrocephalus, abscess formation, granulomas, and enhancement of the basal meninges with contrast administration.

Syphilis

Ophthalmic presentations of syphilis include papillitis, retinal hemorrhages, arterial and venous occlusions, vasculitis, chorioretinitis, necrotizing vasculitis, optic neuritis, and uveitis. Meningovascular syphilis produces visual field defects and ocular motility disorders (ocular motor cranial nerve palsies) in some patients.

Syphilis may accompany HIV infection, creating a diagnostic challenge in immunocompromised patients. The CSF may show one or more of the following changes: positive syphilis serology, elevated protein level, or pleocytosis. However, both false-negative and false-positive serologic results are more common in the patient infected with HIV. The CSF VDRL test alone cannot be relied upon to confirm CNS infection. A course of aqueous penicillin G (12–24 million U/day IV for 10–14 days) is recommended, with reexamination of the CSF to determine the effectiveness of treatment.

Progressive Multifocal Leukoencephalopathy

Originally described in patients with lymphoproliferative disorders and impaired cell-mediated immunity, progressive multifocal leukoencephalopathy (PML) has also been described in patients treated with immunomodulating medications such as natalizumab and occurs in 1%–4% of HIVinfected patients. The disease is caused by the JC virus, a polyomavirus that destroys oligodendrocytes. Gray matter is relatively spared. The central visual pathways and ocular motor fibers can be affected. Neuro-ophthalmic manifestations include homonymous hemianopia, blurred vision, cerebral blindness, prosopagnosia, and diplopia. Other neurologic findings are altered mental status, ataxia, dementia, hemiparesis, and focal deficits.

MRI scan shows areas of demyelination, most frequently in the parieto-occipital region. PML typically involves the subcortical white matter, with focal or confluent nonenhancing lesions (Fig 1420). Therapy is aimed at correcting the underlying immune deficiency state, and prognosis is poor. In some cases plasma exchange may be helpful.

Figure 14-20 Progressive multifocal leukoencephalopathy (PML) in a patient with AIDS. A, Axial FLAIR image demonstrates increased signal in the left occipital lobe white matter and extending anteriorly. B, Axial gadoliniumenhanced T1-weighted spin echo image (same location as part A) demonstrates a nonenhancing hypointense lesion in the left occipital white matter. T1 hypointensity is typical of PML lesions. Note the absence of mass effect and negligible

enhancement. (Courtesy of Joel Curé, MD.)

Toxoplasmosis

CNS toxoplasmosis is often associated with immune deficiency. Toxoplasmic optic neuritis is rare, characterized by subacute visual loss and optic nerve swelling, at times accompanied by a macular star (neuroretinitis). CNS toxoplasmosis produces multifocal lesions, with a predilection for the basal ganglia and the frontal, parietal, and occipital lobes. Patients experience headaches, focal neurologic deficits, seizures, mental status changes, and fever. Neuro-ophthalmic findings include homonymous hemianopia and quadrantanopia, ocular motor palsies, and gaze palsies. Lifelong antitoxoplasmosis treatment is necessary to prevent recurrences.

MRI typically shows multiple lesions that are isointense with the brain on T1-weighted images and isointense or hyperintense on T2-weighted images. Gadolinium administration reveals enhancement.

Lyme Disease

Lyme borreliosis is caused by infection with Borrelia burgdorferi, a spirochete transmitted by deer ticks. The disease typically occurs in 3 stages and can produce ocular and neuro-ophthalmic

manifestations. Lyme disease is discussed further in BCSC Section 1, Update on General Medicine, and Section 9, Intraocular Inflammation and Uveitis.

In stage 1, 60%–80% of patients have a localized infection characterized by a skin rash (erythema chronicum migrans) that is sometimes associated with fever, regional lymphadenopathy, and minor constitutional symptoms (Fig 14-21). This stage typically occurs within days or weeks of infection. The ocular findings include conjunctivitis, photophobia, periorbital edema, diffuse choroiditis, exudative retinal detachment, and iridocyclitis.