Limbic encephalitis in a myasthenic patient

The patient is a 69-year-old man, recovered for confusion, amnesia, aphasia and hypophonia. All symptoms suddenly developed 2 weeks before admission, after a mild gastroenteritis. Since 1990, he was being treated (pyridostigmine 1/4 4/die and imuran for 7 years) for generalized myasthenia gravis. No evidence of thymoma was found and the clinical condition remained satisfactory until February 2000. On admission CT scan revealed hyperdense areas bilaterally at temporal lobes, without contrast enhancement. Electroencephalography revealed paroxysms in temporal regions on both sides. The patient underwent lumbar puncture in order to identify viral genome in the CSF, and he was treated with acyclovir i.v. 10 days along ex iuvantibus. CSF exam results were compatible with hematoencephalic wall damn (4 cells/mm³, proteins 58 mg/dl, CSF vs. serum albumin 8.83). PCR on CSF was negative for all genome searched (papovavirus JC and BK, adenovirus, enterovirus, CMV, EBV, HSV 1 and 2). Mycobacterial infection was excluded. In the first week, we conducted neuropsychological tests, which showed transcortical sensory aphasia (anomic aphasia, circumlocution, deficits of comprehension on the Token test). Head MRI demonstrated other similar lesions in the frontal lobe on both sides and left insula: these aspects are pathognomic for limbic encephalitis, confirmed by a second lumbar puncture executed 2 weeks after the CT scan, that definitively excluded viral infection. We investigated a malignancy and began treating the patient with corticosteroids per os. The myasthenia gravis correlated condition remained stationary. Thoracic CT excluded thymoma or lung cancer. Blood neoplastic markers were negative, and so was the search for anti-cerebella antibodies (anti-Hu, anti-Ro and others). At the same time, the treatment gave a good recovery of the patient. In fact, we controlled the patient in time through neuropsychological tests, head MRI and electroencephalography. In particular, a month later neuropsychological tests showed that the patient had improved (no more aphasia, only low amnesic deficits). One month later electroencephalography wasn't altered by paroxysms yet. Two months later head MRI revealed no lesions in frontal lobes and consistent reduction of the other altered areas. Limbic encephalitis with a lack of malignancy is a rare condition. In addition, the patient presents an autoimmune disease. Similar conditions were described by T. Kusuhara et al. in 1995 in [Non-herpetic acute limbic encephalitis] (Rinsho Shinkeigaku 1994 Nov; 34 (11):1083-8) and especially by N. Khan and H.G. Wieser in Limbic encephalitis: a case report (Epilepsy Res 1994 Feb; 17(2): 175-81). The last one describes in 1994 a patient with a clinical course very similar to our patient.