Neurodiagnostic studies in autoimmune encephalitis

Albert DV, Pluto CP, Weber A, Vidaurre J, Barbar-Smiley F, Abdul Aziz R, Driest K, Bout-Tabaku S, Ruess L, Rusin JA, Morgan-Followell B. Utility of Neurodiagnostic Studies in the Diagnosis of Autoimmune Encephalitis in Children.  Pediatr Neurol. 2016 Feb;55:37-45.

Abstract

BACKGROUND:

Autoimmune encephalitis is currently a clinical diagnosis without widely accepted diagnostic criteria, often leading to a delay in diagnosis. The utility of magnetic resonance imaging (MRI) and electroencephalography (EEG) in this disease is unknown. The objective of this study was to identify disease-specific patterns of neurodiagnostic studies (MRI and EEG) for autoimmune encephalitis in children.

METHODS:

We completed a retrospective chart review of encephalopathic patients seen at a large pediatric hospital over a four year interval. Clinical presentation, autoantibody status, and MRI and EEG findings were identified and compared. Individuals with autoantibodies were considered "definite" cases, whereas those without antibodies or those with only thyroperoxidase antibodies were characterized as "suspected."

RESULTS:

Eighteen patients met the inclusion criteria and autoantibodies were identified in nine of these. The patients with definite autoimmune encephalitis had MRI abnormalities within limbic structures, most notably the anteromedial temporal lobes (56%). Only individuals with suspected disease had nontemporal lobe cortical lesions. Sixteen patients had an EEG and 13 (81%) of these were abnormal. The most common findings were abnormal background rhythm (63%), generalized slowing (50%), focal slowing (43%), and focal epileptiform discharges (31%). Sleep spindle abnormalities occurred in 38% of patients. There were no specific differences in the EEG findings between the definite and suspected cases. Focal EEG findings only correlated with a focal lesion on MRI in a single definite case.

CONCLUSIONS:

Pediatric patients with definite autoimmune encephalitis have a narrow spectrum of MRI abnormalities. Conversely, EEG abnormalities are mostly nonspecific. All patients in our cohort had abnormalities on one or both of these neurodiagnostic studies.
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From the paper:

The most common presenting symptom was seizure (56%). Fever was documented on clinical presentation in 33%. Seventeen of 18 patients had cerebrospinal fluid (CSF) examination. Ten (56%) of those had five or more leukocytes per cubic millimeter. Six (33%) of 17 had CSF protein greater than 45 mg/dL. Both leukocytes and protein were adjusted for number of red blood cells (RBCs) using the standard correction calculation (allowance of one leukocyte for every 700 RBCs and protein increases 1.1 mg/dL for every 1000 RBCs). Eight patients had testing for oligoclonal bands. Unpaired oligoclonal bands were present in the CSF of four. Six patients had other autoimmune disorders: one type I diabetes mellitus, three transient thyroiditis associated with anti-thyroperoxidase (TPO) antibodies, one alopecia areata, and one type I diabetes mellitus and Grave disease. Mean duration of follow-up was 25 months (range 1 to 79 months).

Antibody testing was performed at the discretion of the treating physician and was, therefore, highly variable. NSAbs were identified in five patients, and all these were anti–N-methyl- d -aspartate (NMDA) receptor antibodies. GAD antibodies (GAD65) were identified in four patients. In all, we identified nine definite cases of autoimmune encephalitis via antibody testing in either serum or CSF. All other cases were classified as suspected cases based on the fulfillment of clinical inclusion criteria. Given the poorly understood significance of TPO antibodies, patients with TPO antibodies alone were classified as suspected….

Thirteen of 17 (76%) had an abnormal MRI of the brain. Seven of the nine patients (78%) with definite autoimmune encephalitis had abnormalities on initial brain MRIs. Increased T2 signal on fluid-attenuated inversion recovery images was the predominant MRI abnormality, seen in all patients with an abnormal MRI…

The occurrence of abnormal sleep spindle abnormalities in 38% of the patients was a novel finding. This was present in 38% of all patients. Both asynchrony and prolongation of sleep spindles were noted. We specifically examined the recordings for the extreme delta brush pattern that has been described in adults with anti-NMDA receptor encephalitis and did not find this pattern in any of our study patients.