Autoimmune encephalitis with GABAB antibodies, thymoma, and GABAB receptor thymic expression
子宮頸がんワクチンの副反応とは無関係ですが、GABA受容体の抗体が陽性だった脳炎の症例報告
Antibody-mediated autoimmune encephalopathies comprise a group of severe conditions with a varying degree of motor and cognitive symptoms that respond to immunotherapies.1 The associated antibodies are directed against intracellular targets, such as the classic paraneoplastic autoantigens Hu, Yo, Ri, CV2, Ma2/Ta, or the enzyme GAD, or against cell surface antigens such as receptors and ion channels.
A newly described pathogenic antibody in autoimmune encephalopathies is directed against the γ-aminobutyric acid receptor B (GABAB), a G-protein–coupled receptor.2 In 2 large series of more than 35 GABAB-seropositive patients, the most common symptoms were limbic encephalitis, seizures, ataxia, and opsoclonus myoclonus3,4; only a single case presented with brainstem encephalitis.5 The GABAB-associated syndrome can be also paraneoplastic up to 35% of the cases, most often associated with small-cell lung cancer and quite often in conjunction with another paraneoplastic antibody.
We present a case of GABAB-associated autoimmune encephalopathy with brainstem manifestations, thymoma, and co-occurrence of anti-Hu and anti-CV2 antibodies. The main novelty of the case is GABAB expression in the thymus, implicating reactivity against the same antigen between thymus and brain.
Case presentation.
A 25-year-old man was admitted for evaluation of recurrent episodes of vertigo, dizziness, persistent hiccups, nausea, and vomiting that started 3 months prior to admission. On admission he had normal cognitive functions, horizontal nystagmus intensified to the left, brisk tendon reflexes in the lower limbs, positive Romberg sign, and tongue myoclonus. After 1 week he developed right sixth nerve palsy with diplopia, and 2 weeks later he developed left third nerve palsy.