Anti-GABAB (gamma aminobutyric acid-B) receptor encephalitis is an autoimmune disease mediated by GABAB -related antibodies and often involves the limbic system. GABA is the major inhibitory neurotransmitter in the CNS. It is widely distributed in the brain and plays a principal role in reducing neuronal excitability throughout the CNS. There is evidence that disruption of the GABAB-R structure and function can cause spontaneous seizures. In vitro studies have found that antibodies in the CSF of patients with anti- GABAB receptor encephalitis can prevent the activation of the GABAB receptor and block its function. The disease is linked to lung cancer, which requires long-term follow-up observation.
Anti-GABABR encephalitis affects mostly men, but it is seen in women also.
The onset of Anti-GABABR encephalitis is relatively sudden. Before disease onset, some patients might experience fever and non-specific respiratory symptoms. This type of AE presents with epilepsy, cognitive dysfunction, and mental behavioral abnormalities, and epilepsy is often the first symptom.
In a recent study (Zhu et al) it was found that 100% of the patients had epilepsy, with frequent attacks occurring up to four to five times/day. A majority of patients had mental behavioral abnormalities and character alterations. Mental behavioral abnormalities manifested as non-sensical and forced behaviors. Personality changes manifested as a loss of interest in things, a worsened temper, increased aggressive behaviors such as beating and scolding people, high emotional instability, and an increased tendency to become sad.
Antibodies (mainly IgG1) against GABAB receptor are found in serum or CSF. In the majority of patients oligoclonal bands are found in the CSF and 24h IgG levels are increased in 92% of patients. EEG results often indicated slow waves, sharp waves, or spike waves in temporal areas. Brain MRI showed abnormalities in the medial temporal lobe, hippocampus, and amygdala.
Approximately 50% of patients are diagnosed with small cell lung cancer, and in rare cases, thymoma, malignant melanoma, breast carcinoma, and others have also been found.
Treatment consists of first-line immunotherapy (IVIG and corticosteroids) and treatment specific to the tumor, if present (chemotherapy and radiation therapy). Antiepileptic medicines are often part of a treatment plan.
The limited number of patients reported in literature have indicated that patients with anti-GABABR encephalitis can do well with immunotherapy, especially when no tumor is present or the tumor is treatable.