Unilateral involuntary movements of the limbs with caudate nucleus restricted diffusion on magnetic resonance imaging: A case report

Abstract

Anti-leucine-rich glioma-inactivated-1 (LGI1) autoimmune encephalitis is one of the most prevalent forms of autoantibody-associated limbic encephalitis. Brain magnetic resonance imaging of patients with anti-LGI1 encephalitis often presents as fluid-attenuated inversion recovery hyperintensities of the medial temporal lobe. We report the case of a man in his early 60s who suddenly experienced involuntary movement of the right limbs. Brain magnetic resonance imaging revealed normal T1 signal and T2 hyperintensity in the left caudate nucleus, with corresponding fluid-attenuated inversion recovery hyperintensity, diffusion-weighted imaging hyperintensity, and apparent diffusion coefficient hypointensity. The patient was ultimately diagnosed with anti-LGI1 autoimmune encephalitis. For patients with unilateral involuntary movement accompanied by restricted diffusion in the basal ganglia region, anti-LGI1 encephalitis should be considered.

Introduction

Anti-leucine-rich glioma-inactivated-1 (LGI1) autoimmune encephalitis is one of the most prevalent forms of autoantibody-associated limbic encephalitis, initially described in 2010.^1,2 The underlying pathogenesis of anti-LGI1 encephalitis remains unclear. It often presents with acute or subacute onset and is more prevalent among middle-aged and older men. The most common manifestation of anti-LGI1 encephalitis is faciobrachial dystonic seizures (FBDS). ³ Brain magnetic resonance imaging (MRI) of patients with anti-LGI1 encephalitis often presents as fluid-attenuated inversion recovery (FLAIR) hyperintensities of the medial temporal lobe and involves the basal ganglia. High metabolism is detected on positron emission tomography (PET)/computed tomography. ⁴ Unilateral lesions with restricted diffusion have rarely been reported. ⁵

Case report

A man in his early 60s who presented with a sudden decrease in the level of consciousness and brachial dystonic seizures for 5 h was admitted to the Sichuan Academy of Medical Sciences and Sichuan Provincial People’s Hospital in September 2024. The patient reported hypertension, which was well-controlled with long-term antihypertension medication, and a 40-year history of alcohol use. He had no history of cognitive impairment, diabetes, or smoking. Neurological examination was notable for drowsiness and recurrent involuntary movements of the right limbs. Muscle strength was intact. Cognitive function was assessed using the Mini-Mental State Examination (MMSE) and the Montreal Cognitive Assessment (MoCA). The patient scored 26/30 on the MMSE and 19/30 on the MoCA. No education-adjusted scoring was applied. Laboratory tests showed no significant abnormalities (admission blood glucose was normal). Brain MRI revealed normal T1 signal characteristics and T2 hyperintensity in the left caudate nucleus, with corresponding FLAIR hyperintensity, diffusion-weighted imaging hyperintensity, and apparent diffusion coefficient (ADC) hypointensity in the same region (Figure 1). Intracranial magnetic resonance angiography appeared normal. Cerebrospinal fluid (CSF) analysis revealed normal protein concentration (0.24 g/L) and cell count (nucleated cell count <2.5 cells/mm³) and an elevated glucose level (4.41 mmol/L; simultaneous fingertip glucose level: 8.9 mmol/L). CSF acid-fast staining, Indian ink staining, and bacterial cultures were negative. CSF and serum autoimmune encephalitis antibodies were screened, including AMPAR, LGI1, Caspr2, GABABR, DPPX, IgLON5, GlyRα1, GABAARα1, GABAARβ3, mGluR1, mGluR5, D2R, Neurexin-3α, GAD65, KLHL11, gACHR, and NMDAR. Antibodies against LGI1 were positive in both the patient’s serum (1:3200) and CSF (1:32). On day 4 of hospitalization, the patient received intravenous methylprednisolone therapy (1 g/day for 3 days, followed by 0.5 g/day for 3 days and 0.25 g/day for another 3 days). On day 7 of hospitalization, a marked improvement in unilateral involuntary movements of the right limbs was observed. The patient was discharged on day 11 of hospitalization with a prescription of oral prednisone (60 mg daily), which was tapered gradually. Post-discharge, the symptoms remained stable with no relapse. We have de-identified all patient details. Written informed consent (consent to treatment and publication) was obtained from the patient, and the reporting of this study conforms to the Case Report (CARE) guidelines. ⁶

Figure 1.

Noncontrast CT and brain MRI of the patient. Normal initial noncontrast CT image at the level of the basal ganglia showing no density changes (a). T1-weighted image showing normal signal characteristics in the left caudate nucleus (b). T2 and FLAIR axial images showing bright signal intensity in the same region (c and d). Injury is characterized by diffusion restriction at the same level on diffusion-weighted imaging (e) and ADC images (f). ADC: apparent diffusion coefficient; CT: computed tomography; FLAIR: fluid-attenuated inversion recovery; MRI: magnetic resonance imaging.

Discussion

Anti-LGI1 encephalitis is a common form of autoimmune encephalitis, typically presenting with subacute cognitive impairment and epilepsy, with FBDS being the most distinctive clinical feature.

FBDS is one of the relative characteristic manifestations of anti-LGI1 encephalitis and occurs in 40%–50% of patients with anti-LGI1 encephalitis. ³ FBDS often manifests as frequent and brief (only a few seconds) muscle tone disorder-like involuntary movements on one side of the face, arms, and even lower limbs. In terms of clinical manifestations, differential diagnosis should be considered for FBDS including hemichorea associated with non-ketotic hyperglycemia (HNKH) and acute ischemic stroke (AIS). Manifestations of HNKH include rapid, irregular, involuntary dance-like movements of one or both limbs as well as abnormal facial expressions. Patients with HNKH typically show high signal intensity in the basal ganglia on brain MRI T1-weighted imaging. AIS in the basal ganglia region can manifest as hemichorea but is often seen in the older population and patients with vascular risk factors. Typical brain MRI diffusion-weighted images of patients with AIS exhibit high signal intensity.

Brain lesions in patients with anti-LGI1 encephalitis almost universally involve the temporal lobes, although occasional involvement of the entorhinal cortex, insula, parahippocampal gyrus, piriform gyrus, temporal pole, and precuneus has been reported. A previous study reported that neither T2 FLAIR hyperintensities nor pre-contrast T1 hyperintensities were observed in the basal ganglia of patients with anti-LGI1 autoimmune encephalitis. ⁷ Notably, in this study, diffusion restriction with apparent diffusion coefficient hypointensities was absent in LGI1 cases. T2 FLAIR hyperintensities in patients with LGI1/CASPR2 autoimmune encephalitis were typically confined to the temporal lobes, with no diffusion restriction and only rare contrast enhancement. However, it is noteworthy that LGI1 is highly expressed in human basal ganglia, and fluorodeoxyglucose PET studies have repeatedly shown metabolic alterations in these regions. ⁴ Most importantly, these lesions may exhibit diffusion restriction, although the underlying mechanisms remain unclear.

Conclusion

For patients with unilateral involuntary movement accompanied by restricted diffusion in the basal ganglia region, anti-LGI1 encephalitis should be considered in addition to AIS.