S61. Electroencephalography patterns in patients with thymoma and limbic autoimmune encephalitis: Report of three cases

Abstract

Introduction Although Myasthenia gravis (MG) is the most common autoimmune disease associated with thymoma, a small proportion of thymomatous patients can suffer from limbic autoimmune encephalitis (LE). LE is usually characterized by rapid progressive short-term memory deficits, psychiatric symptoms, and seizures. Patients can present antibodies against cell surface antigens, including contactin-associated protein-like 2 (CASPR2) and a-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPAR). Our aim was to analyze the EEG findings of these patients to find possible EEG homologies among their patterns. Methods Clinical information was obtained from a retrospective review of medical records and EEG recordings of three patients with thymoma and LE: two with seropositivity for AMPAR antibodies and one for CASPR2 antibodies. Results The first case was a 37 years-old man with a subacute onset of memory loss, confusion, anxiety and behavioral disorders in the setting of an invasive thymoma (type B2-B3). Brain MRI and dosage of acetylcholine receptor antibodies (AChR-Abs) were normal. EEG showed bilateral fronto-temporal spikes together with slow theta and delta activity. Clinical suspicion of a paraneoplastic neurological syndrome associated with thymoma was confirmed by the serological presence of AMPAR-Abs. The second case was a 47 years-old female patient with Myasthenia Gravis (MG) and seropositivity for AChR-Abs, treated for recurrent thymoma (type B2). She presented three episodes of generalized seizures, together with mental disorientation, impairment of recent memory and insomnia. Brain MRI was normal. EEG showed a peculiar pattern, comprising lateralized right fronto-temporal spikes and generalized sharp waves. Serological tests detected the presence of antibodies to CASPR2. The third case was a 52 years-old female patient with thymoma (type B2-B3) who developed confusion, short-term memory loss and psychomotor agitation after thymectomy. Cerebrospinal fluid (CSF) examination showed a mild blood-CSF barrier damage and brain MRI revealed increased T2 signal involving mesio-temporal cortical areas. EEG showed electrical abnormalities in the fronto-temporal regions. Antibodies to the glutamate receptor 1 (GluR1) and GluR3 subunits of AMPAR were detected both in serum and CSF. Conclusion Limbic autoimmune encephalitis should be suspected in patients with invasive thymoma and subacute onset of confusion, memory loss and seizures. In all these three cases EEG showed epileptiform activity, especially in the fronto-temporal regions, together with slow theta and delta activity, without a pathognomonic pattern. Our results strongly emphasize the importance of testing biological samples when a possible autoimmune CNS involvement is suspected. Even if antibody testing remains the cornerstone in the diagnostic pathway, EEG is paramount in the differential diagnosis with similar disorders, in orienting toward limbic encephalopathy, especially when MRI is inconclusive.