Chorea, Ataxia, and Disturbed Sleep

A 72-year-old man sought care for predominant choreiform movements, mild gait ataxia, urinary dysfunction, and abnormal nocturnal behaviors. Choreiform movements were nearly constant while awake, vanished during sleep, and predominantly involved his lower extremities and trunk. He also had urinary dysfunction, with urinary hesitancy and frequency. Sleep-related behaviors included sleep talking, sleep singing, sudden single-limb jerking movements, and complex hand movements. He also had daytime sleepiness. On neurologic examination, abnormal findings included postural instability at baseline with eyes open and a slightly wide-based tentative gait and inability to execute tandem walking. He had intermittent choreiform movements of the legs and the left shoulder. He also had occasional repetitive, periodic, voluntary-appearing, triple flexion–type movements of both legs. Overnight polysomnography was ordered to evaluate nocturnal movements. Polysomnography revealed rapid periodic leg movements of sleep and rapid eye movement sleep without atonia. Sleep architecture was mildly deranged, with electroencephalographic alpha intrusion throughout nonrapid eye movement sleep, as well as absent slow-wave sleep. Ferritin level was suboptimal. Evaluation of serum for autoimmune encephalitis demonstrated IgLON family member 5 antibody positivity by tissue immunofluorescence assay, confirmed by cell-based assay. The patient was diagnosed with IgLON family member 5 autoimmune encephalitis and symptomatic rapid eye movement sleep behavior disorder. The patient was instructed to maintain a safe sleep environment at home and to begin taking melatonin at bedtime. A therapeutic trial of intravenous methylprednisolone, together with mycophenolate mofetil, was followed by improvement in memory, confusion, and hallucinations, waking involuntary movements, bladder dysfunction, and sleep quality. Rapid eye movement sleep behavior disorder is a parasomnia characterized by rapid eye movement sleep without atonia, the loss or dysregulation of normal rapid eye movement sleep atonia, which is its pathophysiologic signature, and which is permissive for dream enactment behaviors during rapid eye movement sleep.