Emmanuel Mignot, Pierre Labauge, Virginie Desestret, Matthew Murnane, Jérôme Honnorat, Claire Nocon, Clément Vialatte De Pémille, Thomas De Broucker, Anne-Laurie Pinto, Bastien Joubert, Irina Taifas, Sergio Muñiz-Castrillo, Valentin Wucher, Marie Benaiteau, Aditya Ambati, Julien Hedou, David M. Jones, Valérie Dubois, Laura Fechtenbaum, Alberto Vogrig, Dimitri Psimaras, Hospices Civils de Lyon (HCL), Institut NeuroMyoGène (INMG), Université Claude Bernard Lyon 1 (UCBL), Université de Lyon-Université de Lyon-Institut National de la Santé et de la Recherche Médicale (INSERM)-Centre National de la Recherche Scientifique (CNRS), Stanford University, Albany Medical College, Centre Hospitalier Universitaire de Toulouse (CHU Toulouse), Centre Hospitalier de Saint-Denis [Ile-de-France], Centre Hospitalier Henri Mondor d'Aurillac, Centre Hospitalier Régional Universitaire [Montpellier] (CHRU Montpellier), Université de Montpellier (UM), Centre Hospitalier de Dax, Hôpital d'instruction des Armées Percy, Service de Santé des Armées, Groupe Hospitalier Paris Saint-Joseph (hpsj), CHU Pitié-Salpêtrière [AP-HP], Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Sorbonne Université (SU), Institut du Cerveau = Paris Brain Institute (ICM), Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Institut National de la Santé et de la Recherche Médicale (INSERM)-CHU Pitié-Salpêtrière [AP-HP], Assistance publique - Hôpitaux de Paris (AP-HP) (AP-HP)-Sorbonne Université (SU)-Sorbonne Université (SU)-Sorbonne Université (SU)-Centre National de la Recherche Scientifique (CNRS), Etablissement français du sang - Auvergne-Rhône-Alpes (EFS), and Retiveau, Nolwenn
Limbic encephalitis with antibodies against adenylate kinase 5 (AK5) has been difficult to characterize because of its rarity. In this study, we identified 10 new cases and reviewed 16 previously reported patients, investigating clinical features, IgG subclasses, human leucocyte antigen and CSF proteomic profiles. Patients with anti-AK5 limbic encephalitis were mostly male (20/26, 76.9%) with a median age of 66 years (range 48–94). The predominant symptom was severe episodic amnesia in all patients, and this was frequently associated with depression (17/25, 68.0%). Weight loss, asthenia and anorexia were also highly characteristic, being present in 11/25 (44.0%) patients. Although epilepsy was always lacking at disease onset, seizures developed later in a subset of patients (4/25, 16.0%). All patients presented CSF abnormalities, such as pleocytosis (18/25, 72.0%), oligoclonal bands (18/25, 72.0%) and increased Tau (11/14, 78.6%). Temporal lobe hyperintensities were almost always present at disease onset (23/26, 88.5%), evolving nearly invariably towards severe atrophy in subsequent MRIs (17/19, 89.5%). This finding was in line with a poor response to immunotherapy, with only 5/25 (20.0%) patients responding. IgG1 was the predominant subclass, being the most frequently detected and the one with the highest titres in nine CSF-serum paired samples. A temporal biopsy from one of our new cases showed massive lymphocytic infiltrates dominated by both CD4+ and CT8+ T cells, intense granzyme B expression and abundant macrophages/microglia. Human leucocyte antigen (HLA) analysis in 11 patients showed a striking association with HLA-B*08:01 [7/11, 63.6%; odds ratio (OR) = 13.4, 95% confidence interval (CI): 3.8–47.4], C*07:01 (8/11, 72.7%; OR = 11.0, 95% CI: 2.9–42.5), DRB1*03:01 (8/11, 72.7%; OR = 14.4, 95% CI: 3.7–55.7), DQB1*02:01 (8/11, 72.7%; OR = 13.5, 95% CI: 3.5–52.0) and DQA1*05:01 (8/11, 72.7%; OR = 14.4, 95% CI: 3.7–55.7) alleles, which formed the extended haplotype B8-C7-DR3-DQ2 in 6/11 (54.5%) patients (OR = 16.5, 95% CI: 4.8–57.1). Finally, we compared the CSF proteomic profile of five anti-AK5 patients with that of 40 control subjects and 10 cases with other more common non-paraneoplastic limbic encephalitis (five with antibodies against leucine-rich glioma inactivated 1 and five against contactin-associated protein-like 2), as well as 10 cases with paraneoplastic neurological syndromes (five with antibodies against Yo and five against Ma2). These comparisons revealed 31 and seven significantly upregulated proteins in anti-AK5 limbic encephalitis, respectively mapping to apoptosis pathways and innate/adaptive immune responses. These findings suggest that the clinical manifestations of anti-AK5 limbic encephalitis result from a distinct T cell-mediated pathogenesis, with major cytotoxicity-induced apoptosis leading to a prompt and aggressive neuronal loss, likely explaining the poor prognosis and response to immunotherapy.