A Case of Autoimmune Limbic Encephalitis, Myasthenia Gravis, and Malignant Thymoma
Marjorie Ho1, Jocelyn Kim2, Pamela Davila-siliezar1, Walter Duarte-Celada1
1Neurology, Texas Tech University Health Sciences, 2Medicine, TTUHSC
Objective:
Both anti-glutamic acid decarboxylase 65 (GAD65) limbic encephalitis (LE) and myasthenia gravis (MG) have been associated with thymomas. However, in very rare instances these two autoimmune diseases coexist together. We present a case of MG associated to malignant thymoma, who also developed a challenging case of LE.
Background:
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Design/Methods:
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Results:

A 46-year-old man presented with a 3-month history of transient diplopia and generalized weakness that worsened through the day. He was found to have seropositive MG and started on pyridostigmine; associated with malignant thymoma and underwent surgical resection next month 

Five months later, he developed new onset seizures and following his surgery, he developed agitation and confusion. Seizures were difficult to control. He underwent serial magnetic resonance imaging (MRI) of the brain, which showed multiple evolving subcortical/cortical T2 hyperintense lesions over the next 2 months, none of them with contrast enhancement. The lesions were bilateral, mainly affecting the left temporal lobe, but also affecting the right occipital, and bilateral frontal lobes. The electroencephalogram showed epileptogenicity from the left temporo-occipital region and right frontal area. Cerebrospinal fluid (CSF) did not reveal evidence of infection. Levetiracetam failed to control the seizures, and was later switched to brivaracetam and phenytoin. 

 

Due to concern of autoimmune encephalitis, patient was started on high-dose steroids followed by cyclophosphamide. Serum and CSF autoimmune encephalitis panel yielded a positive result for anti-GAD65. The addition of steroids and anti-epileptic drugs finally controlled the seizure

Conclusions:
This case highlights the rare coexistence of anti-GAD65 limbic encephalitis and MG in the same patient, probably converging together by a malignant thymoma. Anti-GAD65 LE has been associated with seizures and behavioral changes; rarely linked to malignant tumors (4-6%), most commonly thymoma. Only one other cases of anti-GAD encephalitis associated to MG have been reported in the literature.
10.1212/WNL.0000000000216452
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