Adult-onset temporal lobe epilepsy suspicious for autoimmune pathogenesis: Autoantibody prevalence and clinical correlates

Abstract

Temporal lobe adult-onset seizures (TAOS) related to autoimmunity represent an increasingly recognized disease syndrome within the spectrum of epilepsies. In this context, certain autoantibodies (autoABs) were often associated with limbic encephalitis (LE). Here, we aimed to gain insights into (a) the distribution of 'neurological' autoABs (neuroABs, defined as autoABs targeting neuronal surface structures or 'onconeuronal' ABs or anti-glutamate acid decarboxylase 65 (GAD65) autoABs) in a large consecutive TAOS patient cohort, to characterize (b) clinical profiles of seropositive versus seronegative individuals and to find (c) potential evidence for other autoABs. Blood sera/cerebrospinal fluid (CSF) of TAOS patients (n = 800) and healthy donors (n = 27) were analyzed for neuroABs and screened for other autoABs by indirect immunofluorescence on hippocampal/cerebellar sections and immunoblots of whole brain and synaptosome lysates. Serological results were correlated with clinico-neuropsychological features. 13% of TAOS patients (n = 105) were neuroAB+, with anti-GAD65 and anti-N-methyl-D-aspartate receptors (NMDAR) as most frequent autoABs in this group. In our screening tests 25% of neuroAB- patients (n = 199) were positive (screening+), whereas all control samples were negative (n = 27). Intriguingly, key clinico-neuropsychological characteristics including magnetic resonance imaging (MRI) findings, epileptiform electroencephalographic (EEG) activity, and inflammatory cellular infiltrates in CSF were shared to a greater extent by neuroAB+ with neuroAB-/screening+ patients than with neuroAB-/screening- patients. Serological testing in a large consecutive TAOS patient series revealed seropositivity for anti-GAD65 autoABs as the most frequent neuroAB. Intriguingly, neuroAB+ individuals were virtually indistinguishable from neuroAB-/screening+ patients in several major clinical features. In contrast, neuroAB-/screening- TAOS patients differed in many parameters. These data support the potential presence of so far unrecognized autoABs in patients with TAOS.

Fig 1. Representative indirect immunofluorescence Test (IIFT) and immunoblotting results.

(A) Distribution of autoAB titers in neuroAB⁺ patients. Circle sizes are proportional to the number of patients with the respective titres (1:10, 1:32, 1:100, 1:320, 1:1000 or 1:3200). (B) ~20% of neuroAB^- patients are positive either with immunoblot and/or IIFT screening indicating the presence for so far unknown autoABs. (C) Binding patterns of serum samples of neuroAB^- patients on representative simiiform hippocampal sections: (a) neuronal cytoplasmatic (b) general neuronal (c) neuropil and (d) neuronal nuclear binding pattern (all scale bars: 100 μm). (D) Representative immunoblot of serum from a neuroAB^- patient. Reactivity with lysate of brain from different species is illustrated (h = human, r = rat, m = mouse, s = murine synaptosomes). Two bands (75 kDa and 50 kDa) occur in human, rat and mouse brain lysates. The synaptic fraction shows a band at 75 kDa but not at 50 kDa identifying the putative autoAB-target within the 75 kDa band as component of the synaptic compartment. (E) Distribution of the molecular weight of bands observed in immunoblots of neuroAB^-/screening⁺ patients’ sera and CSF samples. Note the clustering of bands in the 40–80 kDa range (serum: n = 145, CSF: n = 47).

Fig 2. Imaging, semiological and serological parameters of TAOS patients stratified according to autoAB-test status.

(A) NeuroAB⁺ patients have substantially more frequent LE suspicious MRI changes (sLE) comprising signs of edema in amygdala and hippocampus than neuroAB⁺ and neuroAB^-/screening⁺ patients (Chi-square-test group comparison: *p<0.025; ***p<0.0005; neuroAB⁺ n = 98, neuroAB^-/screening⁺ n = 94, neuroAB^-/screening^- n = 92). (B) Representative MRI in a patient with limbic encephalitis and anti-GAD65 autoAB. Coronar T2-weigthed MRI (a) and FLAIR (b) shows swelling and signal increase of the left hippocampus (see white arrows) compared to the contralateral hippocampus. The temporal angulated axial T2-weigth image (c) and the axial FLAIR (d, ac-pc angulation) confirms the increase in volume and size of the left compared to the right hippocampus (see white arrows). (C) The lateralization of MRI changes does not differ between neuroAB⁺ and neuroAB^-/screening⁺ (Chi-square-test group comparison: p = 0.589) or neuroAB⁺ and neuroAB^-/screening^- (Chi-square-test group comparison: p = 0.79; neuroAB⁺ n = 69, neuroAB^-/screening⁺ n = 47, neuroAB^- n = 35). (D) In most of the patients an EEG focus is detectable with no significant differences between the neuroAB⁺ and neuroAB^-/screening⁺ (Chi-square-test group comparison: p = 0.544) or neuroAB⁺ and neuroAB^-/screening^- (Chi-square-test group comparison: p = 0.288; neuroAB⁺ n = 91, neuroAB^-/screening⁺ n = 95, neuroAB^-/screening^- n = 92). (E) A difference concerning affected hemisphere is observed in neuroAB⁺ patients compared to neuroAB^-/screening^- patients (Chi-square-test group comparison: **p<0.005) but not between neuroAB⁺ patients and neuroAB^-/screening⁺ (Chi-square-test group comparison: p = 0.424; neuroAB⁺ n = 60, neuroAB^-/screening⁺ n = 60, neuroAB^-/screening^- n = 53). (F) Most neuroAB⁺ patients have focal impaired awareness seizures in some patients also focal to bilateral tonic clonic seizures occur (Chi-square-test group comparison: neuroAB⁺ compared to neuroAB^-/screening⁺ p = 0.477; neuroAB⁺ compared to neuroAB^-/screening^- p = 0.039; neuroAB⁺ n = 97, neuroAB^-/screening⁺ n = 91, neuroAB^-/screening^- n = 92). (G) In comparison to neuroAB⁺ patients typical CSF changes [elevated protein level (protein increase), pleocytosis, oligoclonal bands and intrathecal IgG synthesis (intrath. IgG)] are present in a similar frequency in neuroAB^-/screening⁺ patients (Chi-square-test group comparison: p = 0.866). In contrast neuroAB^-/screening^- patients have significantly less inflammatory CSF changes (Chi-square-test group comparison: ***p<0.0005; neuroAB⁺ n = 77, neuroAB^-/screening⁺ n = 66, neuroAB^-/screening^- n = 63). sLE–limbic encephalitis suspicious, HS–hippocampal sclerosis, imp. aware–impaired awareness, OCB–oligoclonal bands.

Fig 3. Neurological and psychiatric co-morbidities in TAOS patients.

(A) Memory disturbance, i.e. neuropsychological test results below average, is a common feature throughout the patients stratified according to the serological status with no significant differences between the groups (Chi-square-test group comparison: neuroAB⁺ compared to neuroAB^-/screening⁺ p = 0.284; neuroAB⁺ compared to neuroAB^-/screening^- p = 0.044 neuroAB⁺ n = 95, neuroAB^-/screening⁺ n = 78, neuroAB^-/screening^- n = 93) (B, C) Remarkably, psychosis and depression are not substantially different in frequency between the three groups of patients (Chi-square-test group comparison: psychosis: neuroAB⁺ compared to neuroAB^-/screening⁺ p = 1; neuroAB⁺ compared to neuroAB^-/screening^- p = 0.136/ depression: neuroAB⁺ compared to neuroAB^-/screening⁺ p = 0.461; neuroAB⁺ compared to neuroAB^-/screening^- p = 0.209; neuroAB⁺ n = 99, neuroAB^-/screening⁺ n = 95, neuroAB^-/screening^- n = 93). (D) In contrast, motoric symptoms are substantially more abundant in neuroAB⁺ than in neuroAB^-/screening^- patients (Chi-square-test group comparison: *p<0.025). No significant differences in the presence of these symptoms are discovered between the neuroAB⁺ and neuroAB^-/screening⁺ group (Chi-square-test group comparison: p = 0.147; neuroAB⁺ n = 99, neuroAB^-/screening⁺ n = 95, neuroAB^-/screening^- n = 93).

Fig 4. Co-morbidities of TAOS patients.

(A) Systemic autoimmune syndromes are more abundant than neoplasia in all groups. The neuroAB⁺ group has significant more autoimmune syndromes compared to neoplasia of different entities (Fisher´s exact test: *p<0.016; neuroAB⁺ n = 101). This difference in abundance is not significant in the neuroAB^-/screening^- or neuroAB^-/screening⁺ group (Fisher´s exact test: neuroAB^-/screening⁺ patients: p = 0.805, n = 95; neuroAB^-/screening^- patients: p = 0.434, n = 93). No significant difference is present comparing co-morbidities of seropositive patients with autoABs targeting neuronal surface structures to patients with onconeuronal autoABs (Fisher´s exact test: p = 0.393; surface AB⁺ n = 25, onconeural AB⁺ n = 30). (B) Systemic autoimmunity comprises thyreoditis as most abundant disorder followed by chronic inflammatory bowel disease, collagenosis/chronic polyarthritis and diabetes mellitus type 1 as well as individual autoimmune disorders grouped under ‘other’ (overall n = 47 affected patients).