We report the autopsy fi ndings for a 45-year-old man with polyradiculoneuropathy and fatal acute disseminated encephalomyelitis after having Mycoplasma pneumoniae pneumonia. M. pneumoniae antigens were demonstrated by immunohistochemical analysis of brain tissue, indicating neuroinvasion as an additional pathogenetic mechanism in central neurologic complications of M. pneumoniae infection.A 45-year-old, previously healthy man had fever, pain in the extremities, nasal discharge, and cough with nonpurulent sputum. He sought clinical care 1 week after onset of illness because of his deteriorating general state, including a headache and paresthesias in both hands. Bilateral basal pneumonia was diagnosed and treated with clarithromycin. During the ensuing 4 days, a rapidly ascending polyradiculoneuropathy resulted in tetraparesis, followed by facial palsy, ophthalmoplegia, and then paralysis of all cranial nerves. The initially fully alert patient became comatose, and assisted respiration was necessary.On day 9 of the patient's illness, an ELISA (Genzyme Diagnostics Virotech, Rüsselsheim, Germany) was performed on serum samples and showed a Mycoplasma pneumoniae immunoglobulin (Ig) G antibody titer of 28.2 Virotech-units/mL (VE) (cut-off 9.0-11.0) and an IgM antibody titer of 20.9 VE (cut-off 9.0-11.0). A PCR for M. pneumoniae was positive in tracheobronchial secretions on day 12, and complement fi xation test (antigen purchased from Virion CH-8803 Rüschlikon, Zürich, Switzerland) showed M. pneumoniae antibody titers of 1,280 (serum) and 4 (cerebrospinal fl uid) on day 16.Serologic tests for cytomegalovirus, Epstein-Barr virus, HIV, measles virus, mumps virus, spring-summer encephalitis virus, Borrelia burgdorferi, Brucella spp., Legionella spp., Treponema pallidum, and Toxoplasma gondii were negative. No herpes simplex virus 1 or 2 was detected by PCR in cerebrospinal fl uid, and PCR results were also negative for Chlamydia pneumoniae in tracheobronchial secretions.On day 8, cerebrospinal fl uid examinations showed a total cell count of 43/mm 3 (89% granulocytes and 11% mononuclear cells), total protein 1.3 g/L, and glucose 4.3 mmol/L. On day 15, when the patient was comatose, a total cell count of 794/mm 3 (84% granulocytes and 16% mononuclear cells), total protein 4.6 g/L, and glucose 1.5 mmol/L. Blood values showed leucocytosis with neutrophilia and mild thrombocytosis of 480 g/L.A computed tomographic scan on day 15 showed brain edema and multiple infl ammatory/demyelination lesions in the subcortical white matter of both hemispheres and within the brain thalami, capsulae internae, midbrain, and pons. Electroneurographic and myographic results showed a severe form of a peripheral axonal neuropathy. No antigangliosid (GM) 1 or anti-GM2 antibodies were found in the patient's serum on day 12. We did not look for GQ1b antibodies.The clinical diagnosis was polyradiculoneuropathy (atypical Guillain-Barré syndrome) and acute encephalitis as complications of bilateral pneumonia caused by M. pneumoniae. In addition to c...