Anti-LGI1 encephalitis in a young woman with atypical presentation and faciobrachial dystonic seizures: a case report

Abstract

Case Presentation: A 39-year-old female patient, previously healthy, presented with a three-month history of chills, dizziness, and vomiting. Seven months prior, she developed generalized tonic-clonic seizures, followed by high-frequency left-sided faciobrachial dystonic seizures (FBDS) (multiple episodes per hour) associated with ipsilateral neck pain. On admission neurological examination, she was conscious and oriented; FBDS were observed on examination. Motor assessment showed left hemiparesis (MRC grade IV strength), with ipsilateral tactile hypoesthesia and hypopalesthesia. Brain MRI demonstrated T2/FLAIR hyperintensity in the right hippocampus and uncus, without volumetric atrophy. EEG revealed focal right parietal slowing, without ictal epileptiform activity during motor events. Cerebrospinal fluid showed elevated protein levels (125 mg/dL) and positivity for anti-LGI1 antibodies. Systemic paraneoplastic investigation was negative. The clinical picture stabilized after pulse therapy with methylprednisolone combined with optimization of treatment with levetiracetam and lamotrigine, resulting in complete remission of the FBDS and control of tonic-clonic seizures. Discussion: Anti-LGI1 encephalitis typically affects elderly men (median age >60 years), making this patient’s profile an unusual epidemiological presentation. Unlike the classic presentation, in which FBDS appear as the initial symptom in up to 71% of cases, in this patient, autonomic prodromes and tonic-clonic seizures preceded the dystonic manifestations. This variation underscores the heterogeneity of the clinical spectrum and the need for diagnostic vigilance in young women with limbic symptoms. The pathophysiology involves disruption of the ADAM22/23 transsynaptic complex, resulting in dysfunction of voltage-gated potassium channels (VGKC) and a reduction in AMPA receptors. The observed electroclinical dissociation (frequent FBDS without ictal correlates on EEG) is a well-established finding in over 90% of cases, suggesting an origin in cortico-striatal circuits. Although sodium channel blockers (lamotrigine) aid in controlling seizure threshold, early immunotherapy remains the cornerstone for seizure remission and prevention of structural sequelae. Final Comments: Recognition of FBDS is key to the early diagnosis of anti-LGI1 encephalitis. Refractoriness to antiepileptic drugs and electroclinical dissociation should prompt investigation for neuronal antibodies, regardless of the epidemiological profile or symptom chronology. Prompt initiation of immunotherapy is the primary determinant of seizure remission and reversibility of neuroimaging findings, reducing long-term morbidity.