Objective: To describe a clinical case of a Chorea suspected to be Anti-mGluR5 Antibody-Mediated Secondary to Gastric Cancer

Background: Metabotropic glutamate receptor 5 (mGLUR5) is a neuronal surface receptor associated with autoimmune (AI) syndromes, 60% being paraneoplastic;  45% can present with movement disorders, myoclonus, tremor, dyskinesias and dystonia are described. CSF usually shows mild pleocytosis and MRI can be normal.

Method: Retrospective case analysis

Results: A 67 years old female smoker a history of stroke, migraine and occasional use of metoclopramide and no toxic or antipsychotic exposure; presented with a left hemichorea, hypothymyc mood and anxiety that progressed in 10 months. 

Was initially evaluated in other hospital in Santiago, Chile. Antiphospholipid syndrome (APS) testing, ENA, ANA, Antiestreptolisine O Ab,  CSF biochemical study and AI encephalitis (AE) panel resulted normal and Brain MRI were normal.

Chorea was suspected to be secondary to methoclopramide, for which it was suspended and risperidone and tetrabenazin were started.

She consulted in our center. A left hemichorea, bilateral bradikinesia, hypophonia and hypomimia were noted.

A choreic syndrome and a Pharmacological parkinsonism were diagnosed. 

After risperidone suspension the hemichorea aggravated and an axial dyskinesia was added. She was hospitalized.

She received IVIG and metilprednisolone courses.

Ceruloplasmin, C3, C4, RF, CCP, were normal

γIFN-TBC, HIV, BHV, CHV, AntiDNA Ab, APS study, ENA, ANA and Onconeuronal AI blood panel were negative.

A new AE blood panel (obtained after initiated IVIG) was positive for mGLUR5

A partial improvement was achieved that was not maintained in time. 

Rituximab was started but had a mild response, after 2 months, mycophenolate was started.

After 5 months since IVIG infusion, an epigastric pain, early satiety and nausea started. Abdomen CT and endoscopy revealed peritoneal carcinomatosis and a stenotic gastric lesion. Biopsy confirmed Stage IV gastric adenocarcinoma.

Conclusion: This case depicts mGLUR5 Ab positive chorea that evolves within months that had a poor response to immunosuppressive treatment and within 16 months since diagnosis a gastric cancer was found. Both Gastric cancer and Chorea are not usually associated with mGLUR5. This case shows a possible novel presentation for mGLUR5; also reinforces the importance of active neoplasia screening when Ab have an associated risk.

References: Binks, S., Uy, C., Honnorat, J., & Irani, S. R. (2022). Paraneoplastic neurological syndromes: a practical approach to diagnosis and management. Practical Neurology, 22(1), 19-31.
Spatola, M., Sabater, L., Planagumà, J., Martínez-Hernandez, E., Armangué, T., Prüss, H., … & Dalmau, J. (2018). Encephalitis with mGluR5 antibodies: symptoms and antibody effects. Neurology, 90(22), e1964-e1972.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/anti-mglur5-antibody-mediated-chorea-secondary-to-gastric-cancer-a-case-report/