Extratemporal EEG and MRI findings in ANNA-1 (anti-Hu) encephalitis

Introduction: Extratemporal involvement has been reported in ANNA-1 encephalitis, but the rate is unknown. EEG and MRI are used in the evaluation of these patients, but the relative value of each has not been determined. The study objectives were to measure the rate of extratemporal abnormalities, and to determine the relative value of MRI and EEG in an ANNA-1 encephalitis cohort. Methods: We selected from the neuroimmunology laboratory database ANNA-1 seropositive patients who underwent: (1) neurological evaluation at Mayo Clinic Rochester between 1990 and 2010 (2) comprehensive autoimmune paraneoplastic serological evaluation and (3) at least one EEG and MRI. Results: Of 28 identified patients, the EEG was abnormal in 24 (86%). Extratemporal abnormalities included slowing [12(43%)], epileptiform discharges [eight (29%)], and epilepsia partialis continua [two (7%)]. In ten patients, only the MRI or EEG showed an abnormality but not both. Six patients had focal EEG abnormalities localized to regions other than those on MRI. In 13 patients with a negative MRI, the EEG showed a focal abnormality in seven (54%). Conclusion: Extratemporal EEG abnormalities are present in nearly half of ANNA-1 seropositive patients, suggesting that extratemporal involvement is common. EEG and MRI are often complementary in determining lesional distribution in ANNA-1 seropositive patients.