Abstracts

Rationale: Refining the clinical characterization of autoimmune epilepsy and limbic encephalitis may improve recognition of new cases and guide distinct treatment decisions. The main radiological feature of autoimmune limbic encephalitis consists of bilateral mesial temporal lobe MRI hyperintensities, which in the appropriate clinical context typically triggers a diagnostic workup for antineuronal antibodies (ANAbs) and/or an immunotherapy trial. We describe an additional striking MRI feature in 4 patients consisting of bilateral claustrum hyperintensities, in 2 unaccompanied by temporal lobe hyperintensities. Methods: We collected clinical, neurophysiological and radiological data on 4 patients with claustrum hyperintensities, amongst a cohort of 34 patients with autoimmune limbic encephalitis or epilepsy, either confirmed through ANAb testing or presumed due to characteristic clinical history including dramatic response to immunotherapy. Results: All patients experienced explosive onset of seizures, 2/4 with fever and 3/4 with status epilepticus at the onset of illness. Following resolution of the initial encephalitic state, seizures remained refractory in all patients, despite the requirement of 3 AEDs on average. Semiologies consisted of focal seizures with impairment of awareness, focal seizures with motor components (both positive and negative) and evolution to bilateral convulsive seizures. All patients had cognitive impairment with predominant episodic memory loss. Behavioural changes, ranging from psychosis to mood and anxiety disturbances, were also seen in all patients in the initial phase of their illness, improving on followup in 3/4 patients. CSF lymphocytic pleocytosis was seen in 3/4 patients. ANAbs were identified in 2/4 patients (1 anti-GAD65, 1 anti-Ma2), both of whom showed poor response to immunotherapy (steroids, IVIg +/- plasmapheresis and mycophenolate mofetil). The two other patients with negative ANAbs panels showed a dramatic response to the combination of steroids and IVIg, with rebound increase in seizure frequency during steroid taper or a few weeks after IVIg treatment, responding to a repeat course of immunotherapy. EEG showed frontocentral sharp wave discharges, slow sharp waves or runs of rhythmic delta waves accentuated by hyperventilation in 3/4 patients and bilateral anterior-mid temporal sharp waves in 1/4 patient. All patients displayed T2/FLAIR hyperintensities of the claustrum bilaterally (e.g. Figure 1). There was a delay in the appearance of the hyperintensities, ranging from 1.5-3 weeks in 3/4 patients to 4 months in 1 patient. The initial MRI brain obtained upon hospitalisation was normal in 2 patients, whereas 2/4 patients had bilateral mesial temporal hyperintensities. The claustrum hyperintensities resolved on follow-up imaging in 3/4 patients, on average 4 months after the MRI finding was initially seen. Conclusions: Bilateral claustrum hyperintensities were noted in a group of patients with a constellation of refractory seizures, cognitive impairment and behavioural disturbance, either harbouring ANAbs or displaying a dramatic immunotherapy response. This striking MRI finding may represent a clue to autoimmune limbic encephalitis and subsequent epilepsy. Funding: None.