Autoimmune parkinsonism with faciobrachiocrural dystonic seizures: a new phenotype of leucine-rich glioma-inactivated 1 (LGI1) autoimmunity.

Extrapyramidal symptoms are seen in patients with leucine-rich glioma-inactivated 1 (LGI1) antibody-positive patients infrequently and this can be successfully treated with immunotherapy. This is a retrospective hospital-based study from 2013 to 2021 at a tertiary care referral hospital in South India. LGI1 antibody-positive cases with Faciobrachio-crural dystonic seizures [FBCDS] were identified by reviewing electronic medical records and Neuroimmunology laboratory register. Clinical and laboratory details and treatment outcomes were analysed. There was a total of 23 patients who were positive for LGI1 antibody. Of these, three cases had FBCDS (2 males, age range 30-76 years). Upon reviewing the records they had additional asymmetric parkinsonian features. All had similar presentations with progressive slowness of activities and gait and later went on to have paroxysmal events of sudden falls with vocalization. Prolonged VEEG monitoring captured the habitual event, which were confirmed to be FBCDS. MRI did not show significant structural abnormalities, CSF showed elevated proteins and normal cell in two and lymphocytic pleocytosis in one, PET scans ruled out malignancy. Of the three patients, two were completely relieved of FBCDS with immunosuppression and there was complete resolution of extrapyramidal features in all. Thus, the patients in our series of FBCDS showed additional features of parkinsonism which responded well to immunotherapy. Involvement of basal ganglia can explain all the manifestations of this phenotype. This series reveals a unique phenotype of the LGI1 antibody.