A 62-year-old male with type 2 diabetes mellitus who presented with leg-predominant hyperkinetic movements as initial presentation of LGI1 encephalitis will be described. All clinical and ancillary data were obtained retrospectively by chart review.

Symptoms began with sudden numbness and cramping of his left face, progressing over a few days to involve the left upper and lower extremities. He developed brief, intermittent painless spasms, occurring 30-40 times daily, often causing violent leg jerks that sometimes spread to his left arm and face (video), and led to falls, prompting and emergency department visit. Attacks were triggered by voluntary leg movement and preceded by an “aura” of left-sided numbness and a sense of impending attack, resembling paroxysmal kinesigenic dyskinesia (PKD).  There were no fever, headache, other systemic symptoms, cognitive impairment or psychiatric symptoms. Brain and cervical spine MRI showed nonspecific basal ganglia and pontine calcifications. An electroencephalogram (EEG) captured during attacks was normal. CSF showed a mildly elevated protein (63 mg/dL and 78 mg/dL during the first and second admission, respectively) without pleocytosis. Screening for malignancy (scrotal ultrasound, CT chest/abdomen/pelvic) was unremarkable. The patient did not respond to anticonvulsants and had only a mild response to high-dose intravenous steroids, but improved substantially to plasma exchange. Subsequent serology demonstrated positive LGI1-IgG antibody and a low-titer P/Q-type calcium channel antibody.

Although LGI1 encephalitis is classically associated with faciobrachial dystonic seizures (FBDS)¹, this case highlights that autoimmune encephalitis should be considered even with leg-predominant hyperkinetic manifestations. Early recognition and timely initiation of immunotherapy are critical,² even when initial diagnostic studies are inconclusive. The significance of co-existing low titer P/Q-type calcium channel antibody remains uncertain³. Further studies are needed to clarify its relationship to LGI1 autoimmunity and atypical presentation.