Abstract
CASPR2 Autoimmune encephalitis (AIE) is a heterogenous disease with a male preponderance caused by antibodies against CASPR2: a cellular adhesion molecule part of the neurexin family, heavily concentrated in the limbic system, basal ganglia and temporal lobe, especially in GAD65 positive inhibitory neurons. CASPR2 AIE has variable presentations with both central and peripheral nervous system involvement.
We report the case of a previously high functioning, healthy 67-year-old male with CASPR2 AIE presenting with new onset epilepsy, insomnia and reverse orthostatic myoclonus.
The patient initially presented with nocturnal convulsive seizures and an electroencephalogram (EEG) showed epileptiform discharges consistent with temporal lobe epilepsy. Anticonvulsive medication was initiated. Over the next few weeks, the patient developed short term memory loss, insomnia, propriospinal reverse orthostatic myoclonus (with nocturnal truncal and abdominal myoclonic jerks that abated when sitting or standing), diplopia and ataxia. Examination revealed saccadic intrusions with no horizontal nystagmus, hyperreflexia and truncal and appendicular ataxia. Brain and spinal cord MRI with gadolinium were unremarkable. CSF demonstrated elevated protein and mild mononuclear pleocytosis. Steroid therapy and intravenous immunoglobulin (IVIG) were initiated for AIE: CSF subsequently returned positive for anti-CASPR2 antibodies. The symptoms relapsed requiring a dose of rituximab and course of pulsed methylprednisolone. Follow up at 6 months, the patient showed improvement in cognition, no further seizures, but was still intermittently experiencing reverse orthostatic myoclonus.
In conclusion, we describe a case of CASPR2 AIE that expands the phenotype to include reverse orthostatic myoclonus.
