The usual pattern of neurologic involvement is one of aseptic meningitis or a fluctuating meningoencephalitis with cranial or peripheral neuritis, lasting for months (Reik). By the time the neurologic disturbances appear, the systemic symptoms and skin lesions may have long since receded, usually by many weeks or months. A cardiac disorder, which may accompany or occur independently of the neurologic changes, takes the form of myocarditis, a pericarditis, or atrioventricular block.
The initial nervous system symptoms are rather nonspecific. They consist of headache, mild stiff neck, nausea and vomiting, malaise, and chronic fatigue, fluctuating over a period of weeks to months. Mild meningism without pleocytosis has been seen early in the syndrome and it may be worth repeating the studies in highly suspicious cases. These symptoms relate to the meningitis. There is a CSF lymphocytosis with cell counts from 50 to 3,000/mL and protein levels from 75 to 400 mg/dL, but both values are typically in the lower part of the range. Polymorphonuclear cells may be prominent in the early part of the illness. Usually the glucose content is normal. Somnolence, irritability, faulty memory, depressed mood, and behavioral changes have been interpreted as marks of encephalitis but are difficult to separate from the effects of meningitis. Seizures, choreic movements, cerebellar ataxia, and dementia have been reported but are infrequent. A myelitic syndrome, causing quadriparesis, is also documented as another rare manifestation.
In about half the cases, cranial neuropathies become manifest within weeks of onset of the meningitic illness. The most frequent is a unilateral or bilateral facial palsy but involvement of other cranial nerves, including the abducens and optic nerve has been observed, usually in association with meningitis. One-third to one-half of the patients with meningitis have multiple radicular or peripheral nerve lesions in various combinations. These are described in Chap. 43. In addition to facial palsies, a severe and painful meningoradiculitis of the cauda equina (Bannwarth syndrome) is particularly characteristic and seems to be more common in Europe than in the United States (there are other causes of this syndrome, including herpesvirus and cytomegalovirus). There is also an infrequent occurrence of Guillain-Barré syndrome following Lyme infection, again apparently more common in Europe, but there is no reason to believe that the illness then differs from other cases of the acute inflammatory demyelinating polyneuropathy that follows numerous other infections.
Because of the paucity of autopsy material, knowledge of the nature of Lyme encephalitis is still imprecise. Such pathologic material as is available has shown a perivascular lymphocytic inflammatory process of the leptomeninges and the presence of subcortical and periventricular demyelinative lesions, like those of multiple sclerosis. Oksi and colleagues have recovered B. burgdorferi DNA from the involved areas, suggesting that the encephalitis is caused by direct invasion by the spirochete.
In the peripheral nerves (see Chap. 43) there are scattered lymphocytic infiltrates, without vasculitis. It seems likely to us that the organism will eventually be found in nervous tissue as the cause of disease, as there is active antibody production reflected in the CSF.