CNS manifestations appear in one of 1,000 patients with Mycoplasma pneumoniae-associated infections. Encephalitis is the most frequent manifestation, but cases of meningitis, myelitis, and polyradiculitis, as well as many other symptoms (e.g., coma, ataxia, psychosis, and stroke), have been reported. The onset of these manifestations is usually acute, with lowered consciousness, convulsions, pareses, and other neurological signs. Severe, even fatal, cases are known. The pathophysiology of CNS

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... nifestations is unknown. To our knowledge, M. pneumoniae has never been isolated from brain tissue, but instead it has been recovered from CSF specimens in at least seven cases. Besides direct invasion of M. pneumoniae into the brain, neurotoxic or autoimmune reaction within the brain tissue is suspected. At neuropathological examination, edema, demyelination, and microthrombi have been described. Improved diagnostic methods may reveal the pathophysiology of CNS manifestations associated with M. pneumoniae infection. CNS manifestations are probably the most frequent extrapulmonary complications of infections due to Mycoplasma pneumoniae [1-3] and, as with M. pneumoniae infections in general [4], occur most frequently in children [5, 6]. Still, the incidence of these manifestations is only one per 1,000 patients with M. pneumoniae infections [1]. CNS symptoms are present in up to 7% of patients treated at hospitals for M. pneumoniae infection [6-10]. In turn, among patients with neurological syndromes, M. pneumoniae is associated with 5% to 10% of cases [11, 12] . Severe CNS diseases-even those with fatal outcomes-have been reported in association with M. pneumoniae infections [6, 13-16]. This circumstance emphasizes the need to learn more about these diseases, including their pathophysiology and diagnosis. Therefore, a summary of our own cases and a review of the literature are presented. Summary of Cases Patients and Methods Sixty-one patients, 30 males and 31 females, with neurological diseases were treated at the Children's Hospital or at the Department of Neurology, University of Helsinki, Helsinki, over a 24-year period from January 1967 to December 1990 (figure 1). These patients' diseases were associated with a diagnostic rise (>4-fold) in titer of antibody to M. pneumoniae in paired sera or with a high titer (>64) of this antibody in a single sample of serum. A concomitant high titer of