Glioblastoma as differential diagnosis of autoimmune encephalitis

Objective: To identify the clinical and radiological features that should raise suspicion for the autoimmune encephalitis (AE)-like presentation of glioblastoma. Methods: This is an observational, retrospective case series of patients referred to the French National Reference Center on Paraneoplastic Neurological Diseases for suspected AE (possible, probable or definite, using the 2016 criteria) who later received a final diagnosis of glioblastoma according to 2016 WHO criteria. An extensive literature search was also conducted for similar existing cases. Results: Between 2014 and 2016, 306 patients were referred to our center for suspected AE. Six of these patients (2%) later developed pathologically confirmed glioblastoma. Thirteen patients (9 male) were included for analysis (6 from the present series and 7 from the literature); median age was 63. Initially, a diagnosis of AE was clinically suspected based on: working memory deficits (77%), seizures (62%) (including status epilepticus in 23%), and psychiatric symptoms (46%). Initial brain MRI was not in favor of a typical glioblastoma pattern and showed bilateral (54%) or unilateral selective limbic involvement. Five patients exhibited initial slight contrast enhancement. A clear inflammatory CSF was present in five patients and three from the literature showed autoantibody positivity (NMDAR, VGKC, GluRepsilon2). Median delay between suspicions of AE to GBM diagnosis was 3 months (range 1.5–24) and one patient from the literature was diagnosed post-mortem. Conclusions: An alternative diagnosis of glioblastoma should be considered in patients presenting initially as AE, especially in patients who do not fulfill the criteria for definite AE and in those with a poor clinical evolution despite initial improvement.