Perivenous Encephalomyelitis

Included under the term perivenous encephalomyelitis are several disorders, including ADEM, postinfectious encephalomyelitis, postvaccinial encephalomyelitis, and the most severe hyperacute variant, acute hemorrhagic leukoencephalomyelitis (Hurst disease) (137,152).

ADEM is generally a rare, monophasic, typically nonfatal disorder, most often associated with antecedent illness and is a nonspecific respiratory infection. Some fatal cases have followed measles and smallpox vaccination. In autopsied cases, measles is the most common antecedent illness, followed by rubella, mumps, varicella, and vaccinia. Other mostly nonfatal cases have followed influenza, mycoplasma, infectious mononucleosis, immunization, and the administration of antisera and some drugs. In fatal cases, the brain is grossly swollen, congested, and may show her-niation, and on section may display little apart from swelling and, in some, numerous petechial hemorrhages. Microscopically, widely disseminated, small perivenous lesions are distributed throughout cerebral hemispheres, brain stem, cerebellum, and spinal cord. The lesions are of similar histological age and widely present in white matter, but also involve the deeper cortical layers, and deep gray matter structures. A distinctive feature is the presence of long sleeves of perivenous demyelination surrounded by infiltrates of reactive microglia, within which axons, while preserved relative to myelin, show tortuous and swollen profiles indicating axonal interruption (Figure 12). Narrow zones of subpial ("marginal") demyelination in spinal cord and brain stem (along the anterior median fissure and laterally dorsal to the anterior horns), and rarely in cerebral and cerebellar cortices may be present. An accompanying mild lymphocytic meningitis is invariably present.

Attempts to recover virus from the brain, or to demonstrate viral antigens or viral nucleic acid in ADEM have been negative. The absence of typical viral-associated pathological changes argues against direct invasion of the nervous system by virus as the cause of the disease, while a latent interval between infection or immunization and the onset of the neurological illness and the presence of pathological changes similar to those in acute EAE induced by immunization with white matter or myelin support an autoimmune etiology.

AHL is usually fatal disorder characterized clinically by an abrupt onset of fever, neck stiffness, hemiplegia or other focal signs, seizures, and impaired consciousness. Thankfully, it is rare but has been reported in patients of all ages. Most cases follow an upper respiratory tract infection, typically 1 to 13 days earlier. At autopsy, the brain is congested and swollen, sometimes asymmetrically, and herniation is frequent. Multiple petechial hemorrhages are distributed diffusely throughout the brain. The perivas-cular lesions chiefly consist of ball or ring hemorrhages surrounding necrotic venules, sometimes with fibrinous exudates present within the vessel wall or extending into adjacent tissue. Perivascular cuffs of mononuclear cells with neutrophils are often prominent. Perivenous demyelinating lesions, identical to those of ADEM, may be present. Most authors believe that AHL represents a hyperacute form of ADEM.

0 0

Post a comment