Irani, Sarosh R.

ImportanceAutoimmune encephalitis misdiagnosis can lead to harm.ObjectiveTo determine the diseases misdiagnosed as autoimmune encephalitis and potential reasons for misdiagnosis.Design, Setting, and ParticipantsThis retrospective multicenter study took place from January 1, 2014, to December 31, 2020, at autoimmune encephalitis subspecialty outpatient clinics including Mayo Clinic (n = 44), University of Oxford (n = 18), University of Texas Southwestern (n = 18), University of California, San Francisco (n = 17), Washington University in St Louis (n = 6), and University of Utah (n = 4). Inclusion criteria were adults (age ≥18 years) with a prior autoimmune encephalitis diagnosis at a participating center or other medical facility and a subsequent alternative diagnosis at a participating center. A total of 393 patients were referred with an autoimmune encephalitis diagnosis, and of those, 286 patients with true autoimmune encephalitis were excluded.Main Outcomes and MeasuresData were collected on clinical features, investigations, fulfillment of autoimmune encephalitis criteria, alternative diagnoses, potential contributors to misdiagnosis, and immunotherapy adverse reactions.ResultsA total of 107 patients were misdiagnosed with autoimmune encephalitis, and 77 (72%) did not fulfill diagnostic criteria for autoimmune encephalitis. The median (IQR) age was 48 (35.5-60.5) years and 65 (61%) were female. Correct diagnoses included functional neurologic disorder (27 [25%]), neurodegenerative disease (22 [20.5%]), primary psychiatric disease (19 [18%]), cognitive deficits from comorbidities (11 [10%]), cerebral neoplasm (10 [9.5%]), and other (18 [17%]). Onset was acute/subacute in 56 (52%) or insidious (>3 months) in 51 (48%). Magnetic resonance imaging of the brain was suggestive of encephalitis in 19 of 104 patients (18%) and cerebrospinal fluid (CSF) pleocytosis occurred in 16 of 84 patients (19%). Thyroid peroxidase antibodies were elevated in 24 of 62 patients (39%). Positive neural autoantibodies were more frequent in serum than CSF (48 of 105 [46%] vs 7 of 91 [8%]) and included 1 or more of GAD65 (n = 14), voltage-gated potassium channel complex (LGI1 and CASPR2 negative) (n = 10), N-methyl-d-aspartate receptor by cell-based assay only (n = 10; 6 negative in CSF), and other (n = 18). Adverse reactions from immunotherapies occurred in 17 of 84 patients (20%). Potential contributors to misdiagnosis included overinterpretation of positive serum antibodies (53 [50%]), misinterpretation of functional/psychiatric, or nonspecific cognitive dysfunction as encephalopathy (41 [38%]).Conclusions and RelevanceWhen evaluating for autoimmune encephalitis, a broad differential diagnosis should be considered and misdiagnosis occurs in many settings including at specialized centers. In this study, red flags suggesting alternative diagnoses included an insidious onset, positive nonspecific serum antibody, and failure to fulfill autoimmune encephalitis diagnostic criteria. Autoimmune encephalitis misdiagnosis leads to morbidity from unnecessary immunotherapies and delayed treatment of the correct diagnosis.

Abstract Seizures are a well‐recognized and often prominent manifestation of autoimmune encephalitic syndromes. Progress in detection of pathogenic neural autoantibodies has led to increased awareness of autoimmune causes of seizures. Clinical studies of patients with these autoantibodies have improved our understanding of the seizure characteristics, treatments, and seizure prognosis in these disorders. The International League Against Epilepsy (ILAE) Autoimmunity and Inflammation Taskforce proposes conceptual definitions for two main diagnostic entities: (a) acute symptomatic seizures secondary to autoimmune encephalitis, and (b) autoimmune‐associated epilepsy, the latter of which suggests an enduring predisposition to seizures. Such a distinction is relevant when discussing the pathophysiology, treatment, prognosis, and social consequences of these disorders. We discuss the role of biomarkers in the application of these conceptual definitions and illustrate their use in patients cared for by members of the task force.

ObjectiveDrug‐resistant seizures are common in patients with leucine‐rich, glioma‐inactivated 1 (LGI1)‐IgG associated and contactin‐associated protein‐like 2 (CASPR2)‐IgG associated encephalitis. We performed the first randomized double‐blind placebo‐controlled trial to evaluate efficacy of intravenous immunoglobulin (IVIG) in reducing seizure frequency.MethodsOur enrollment goal was 30 LGI1/CASPR2‐IgG–seropositive adult patients with ≥2 seizures per week. Patients were randomized to receive IVIG (0.5g/kg day 1, 1g/kg day 2, 0.6g/kg weeks 3 and 5) or volume‐matched intravenous normal saline. Following the blinded phase, the nonresponders in the placebo group received IVIG. The primary clinical outcome was 50% reduction in seizure frequency from baseline to 5 weeks.ResultsAfter enrollment of 17 patients (LGI1‐IgG, 14; CASPR2‐IgG, 3) over 34 months, the study was terminated due to slow enrollment. Six of 8 patients in the IVIG group were responders, compared to 2 of 9 in the placebo group (p = 0.044, odds ratio = 10.5, 95% confidence interval = 1.1–98.9). For the LGI1‐IgG seropositive subgroup, 6 of 8 patients in the IVIG group were responders, compared to zero of 6 in the placebo group. Two LGI1‐IgG–seropositive patients receiving IVIG, but none receiving placebo, were seizure‐free at the end of the blinded phase. Four of the 6 patients entering the open‐label IVIG arm reported ≥50% reduction in seizure frequency. There were no correlations with LGI1/CASPR2‐IgG1–4 subclasses.InterpretationSuperiority of IVIG to placebo reached statistical significance for the primary endpoint for all patients and the subset with LGI1‐IgG. These results have to be interpreted with the caveat that the study did not reach its originally selected sample size. ANN NEUROL 2020;87:313–323