Four cases of GABAB receptor encephalitis.

GABAB receptor (gamma-aminobutyric acid type B receptors - GABABR) encephalitis is a rare manifestation of autoimmune encephalitides. We report four cases - including the first two Hungarian patients - with some peculiar features. One patient developed subacute disorientation and almost complete loss of short-term memory, but no epilepsy. Without immunotherapy, his memory spontaneously improved up to mild cognitive impairment in six weeks. GABABR antibodies persisted in his serum, and 18 months later, FDG-PET detected abnormal mediastinal lymph nodes and small cell lung cancer (SCLC). Another patient had persistently decreased sodium content in the peripheral blood. In those three patients who died, CSF was abnormal, but CSF was not pathological in the patient, who spontaneously improved. Brain MRI indicated signal intensity changes in the medial temporal areas in three cases. SCLC was found in three patients. Only the patient, who spontaneously improved, survived for more than 24 months. In summary, our cases show that (i) GABABR encephalitis may develop without epilepsy; (ii) the severe short-term memory loss can spontaneously improve; (iii) persistent hyponatremia can be present in the blood; (iv) the patient with benign course without epilepsy and CSF abnormality survived; (v) spontaneously remitting encephalitis can precede SCLC by 1.5 year, which emphasizes that repeated search for cancer is of paramount importance even in cases with spontaneous improvement.