Progressive Supranuclear Palsy with Post-Traumatic Frontal Lobe Damage Mimicking Anti-IgLON5 Antibody Disease

Phenotypic overlap between autoimmune encephalitis and movement disorders may rarely occur. Anti-IgLON5 antibody mediated disease and progressive supranuclear palsy (PSP) may clinically mimic each other. PSP is one of the tauopathies and a clinicopathologic entity marked by vertical supranuclear gaze palsy, pseudobulbar palsy, symmetric bradykinesia, frontal-subcortical cognitive dysfunction, gait impairment, and postural instability. Anti-IgLON5 antibody mediated disease may also have vertical supranuclear gaze palsy, combined non-REM/REM parasomnias,, bulbar dysfunction (dysarthria, dysphagia, vocal-fold paresis, episodic respiratory failure), gait disturbance, and movement disorder.We present a patient with progressive gait disturbance, vertical supranuclear gaze palsy, cognitive decline, as well as extremity chorea, highlighting the phenotypic overlap between PSP and anti-IgLON5 disease. His workup was negative for the antibody both in serum and cerebrospinal fluid. Fall leading to subdural hemorrhage and bilateral post-traumatic frontal lobe changes likely led to his bilateral upper and lower extremity involuntary movements. His mental status improved after lumbar puncture. His condition further improved on treatment with carbidopa levodopa 25/100 mg three times a day.While the presentation of this case was consistent with anti-IGLON5 antibody mediated disease, the involuntary movements were due to frontal lobe damage.