Objective: We wanted to report the case of a patient with severe subacute cerebellar ataxia related to mGluR1-antibodies with a clear improvement after immunomodulator treatment. Our second objective was to emphase the presence of myoclonus in this rare encephalitis.

Background: Paraneoplasic syndrome is a well-known cause of cerebellar ataxia which is associated with characterized autoantibodies but very rarely with a good outcome of the cerebellar ataxia. Few cases associated to autoantibodies against metabotropic glutamate receptor type 1 (mGluR1-Abs) have been reported although not well documented.

Methods: In November 2016, a 64 years old patient (without remarkable personal or familial medical history) became unsteady but still able to walk without major difficulties. In December he was diagnosed with a Hashimoto thyroiditis. Within the next two months, his instability progressively worsened. In March 2017, he had frequent nearly falls in relation with mild and isolated cerebellar ataxia. Brain MRI was strictly normal. Biological blood analysis, showed a positivity of anti-peroxidase antibodies (> 800) and cerebrospinal fluid (CSF) examination revealed a normal cell count with normal total protein, but positive oligoclonal bands (> 10). Within the two next weeks, the patient could not walk or sit unassisted. Cerebellar ataxia was severe. While sitting or standing, he had severe and diffuse trunk and head myoclonic movements. Gaze examination was normal (no nystagmus or opsoclonus). No other symptoms were found. Anti-Neuropiles autoantibodies were identified in the CSF. The patient was treated with monthly high dose steroids and venous immunoglobulins infusions. He experienced a significant improvement, after four successive monthly therapies; the head and trunk movements disappeared, and the walk was normalized. Only slight right hand dysmetria remained. Finally, mGluR1-Abs were identified as being the anti neuropiles in the CSF.

Results: Our patient shared many similarities with other mGluR1-Abs ataxia cases previously described. Altought head and trunk titubation were frequently descrived (8 out the 12 cases previously mGluR1 encephalitis), these mouvements were not qualified as myoclonus. In our case there was no evidence of paraneoplasic mechanism but the association with Hashimoto‘s disease suggested a possible idiopathic autoimmune dysfunction.

Conclusions: Cerebellitis associated with mGluR1-Abs should be considered in patients with subacute cerebellar ataxia, associated with myoclonus. Immunomodulatory treatment must be administrated as soon as possible because these patients can be cured.

References: 1. Sillevis Smitt P, Kinoshita A, De Leeuw B, et al. Paraneoplastic cerebellar ataxia due to autoantibodies against a glutamate receptor. N Engl J Med. 2000; 6 : 342:21-7. 2. Lopez-Chiriboga AS, Komorowski L, Kümpfel T, Probst C, Hinson SR, Pittock SJ, McKeon A. Metabotropic glutamate receptor type 1 autoimmunity: Clinical features and treatment outcomes. Neurology. 2016 Mar 15;86(11):1009-13.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/mglur1-antibodies-encephalitis-a-rare-cause-of-reversible-ataxia-and-myoclonus-syndrome/