Autoimmune epilepsy: findings on MRI and FDG-PET

Abstract

Although autoimmune epilepsy (AE) is a relatively new concept in the radiology literature, evidence for immunological mechanisms in epilepsy has increased in the last several years. 1-9 AE was originally described in the context of more generalized autoimmune encephalopathy, predominately as a paraneoplastic phenomenon targeting the limbic system. Certain tumors expressing neuronal proteins were found to provoke a cell-mediated neurological disorder as a byproduct of an attack on cancer cells. The classically described paraneoplastic limbic encephalitis (LE) reflects involvement of limbic structures including the anteromedial temporal lobe, hippocampus and amygdala and is clinically characterized by the subacute onset of temporal lobe seizures, anterograde memory impairment and psychiatric symptoms. Similar to other paraneoplastic syndromes, neurologic symptoms can present well before a cancer is detectable. Antibodies traditionally considered paraneoplastic include anti-Hu (ANNA-1) and anti CRMP-5 antibodies, usually found in conjunction with small cell lung carcinoma (SCLC), and anti-N-methyl-Daspartate (NMDA) receptor antibodies which are often associated with ovarian teratoma.

Brain 18F-FDG PET for the diagnosis of autoimmune encephalitis: a systematic review and a meta-analysis

“…18 F-Fluoro-deoxy-glucose ( 18 F-FDG) Position Emission Tomography (PET) is a functional brain imaging technique used to visualize neuronal glycolytic metabolic activity which increases during brain in ammation. Importantly, neurological alterations are associated with lower metabolic activity in speci c areas of the brain 15 . 18 F-FDG PET has also been shown to be superior to morphological imaging in the early diagnosis of autoimmune encephalitis 15 .…”

“…18 F-FDG PET has also been shown to be superior to morphological imaging in the early diagnosis of autoimmune encephalitis 15 . The increasing number of publications studying the results of brain 18 F-FDG PET in autoimmune encephalitis over the past decade is in dire need of consolidation [13][14][15][16][17][18][19][20][21][22][23][24] . The literature is saturated with isolated case-reports and retrospective studies conducted on a small number of patients, leaving the role of PET in the initial assessment of the disease unclear.…”

“…Several previous brain 18 F-FDG PET in autoimmune encephalitis reviews have attempted to report on the additional bene ts of this approach 13,15−25 , but most of these studies focus on the clinical presentation, diagnostic work up, treatments and outcomes even though they all mention 18 F-FDG-PET as a useful investigational tool 14,16,22,25 . Conversely, some reviews do focus on distinct 18 F-FDG-PET imaging patterns associated of the most commonly detected autoantibodies 13,15,[18][19][20][21]24 , albeit without providing a systematic or exhaustive review of cases in the literature or a meta-analysis.…”

Neurofilament light chain levels reflect outcome in a patient with glutamic acid decarboxylase 65 antibody–positive autoimmune encephalitis under immune checkpoint inhibitor therapy

“…Sequential CSF analyses were negative for tumor cells. Although GAD65‐associated encephalopathies usually show significant MRI abnormalities such as temporal lobe involvement, cases with minor MRI alterations (such as in our patient) have also been reported [1,2. Moreover, a recent study by Vogrig et al, in which ICI‐associated CNS side effects were analyzed systematically, showed normal cranial MRI in approximately one‐third of patients with ICI‐induced autoimmune encephalitis [3.…”

Diagnostic Value of Structural and Functional Neuroimaging in Autoimmune Epilepsy

“…Compared with MRI with poor sensitivity, FDG-PET showed more evidence in detecting the progressive stages of anti-NMDAR encephalitis [ 61 ]. The metabolic changes on FDG-PET vary widely and involve all the cerebral lobes, including the temporal and occipital lobes, insular cortex, basal ganglia, hippocampi, striatum, caudate nuclei, cerebellum, and brainstem [ 51 , 62 – 64 ]. The FDG-PET images of anti-NMDAR encephalitis-associated epilepsy showed a pattern of decreased metabolism from the front to the back, that is, high metabolism in the frontal lobe, temporal lobe, and basal ganglia and low metabolism in the parietal occipital lobe, and the metabolic pattern could change with disease progression, treatment, and follow-up [ 63 ].…”