Spontaneous partial resolution of autoimmune-mediated brain MRI abnormalities before immunotherapy in anti-metabotropic glutamate receptor 5 encephalitis: a case report

Abstract

Anti-metabotropic glutamate receptor 5 (mGluR5) encephalitis is a rare autoimmune disorder characterized by varied neurological symptoms, often associated with limbic syndromes. We report the case of a 57-year-old female who presented with obvious ataxia, and then cognitive impairment and behavioral changes. MRI revealed cerebellar dentate nucleus and basal ganglia lesions with enhancement, which spontaneously regressed on follow-up imaging-a rare phenomenon in mGluR5 encephalitis. Diagnosis was confirmed by the presence of serum mGluR5 antibodies. Extensive evaluations excluded underlying malignancies. Immunotherapy, including corticosteroids and intravenous immunoglobulin, led to significant clinical and radiological improvement. This case highlights the unique cerebellar dentate nucleus and basal ganglia involvement and spontaneous partial reduction of lesions in mGluR5 encephalitis, expanding the clinical spectrum of this condition. Early recognition and immunotherapy are crucial for favorable outcomes. Further studies are needed to elucidate the mechanisms behind spontaneous partial lesion regression in autoimmune encephalitis.

Keywords: autoimmune encephalitis; case report; cerebellar dentate nucleus lesions; metabotropic glutamate receptor 5; spontaneous partial regression.

Figure 1

Longitudinal MRI findings in a patient with anti-mGluR5 encephalitis. (A–F) Axial and sagittal FLAIR and contrast-enhanced T1-weighted MRI scans in July 2024 reveal hyperintense lesions in the cerebellar dentate nucleus (A), cerebral peduncle in the mesencephalon and partially mesial temporal area (B), right thalamus and posterior limb of the internal capsule (C, D), with pronounced ring and lobulated-enhancing lesions on contrast images (E, F). However, the patient refused further management. (G–L) MRI scans in August 2024 show partial reduction of hyperintense lesions in the above regions. Minimal residual enhancement remains (K, L), indicating partial resolution of inflammation. Then the patient received immunotherapy, including intravenous immunoglobulins and methylprednisolone. (M–R) MRI scans in January 2025 demonstrate significant resolution of hyperintensities in the cerebellar dentate nucleus (M), cerebral peduncle in the mesencephalon and partially mesial temporal area (N), right thalamus and posterior limb of the internal capsule (O, P) without enhancement (Q, R), corresponding with clinical improvement.