Objective:

To determine the frequency and healthcare expenditure of anti-neural antibody testing for autoimmune encephalitis (AIE) in a large Canadian population. 

Background:

There is increasing interest in and awareness of anti-neural antibody panels for AIE. Emerging research suggests that indiscriminate ordering of anti-neural antibodies for AIE contributes to misdiagnosis and inflated healthcare costs. It is unknown if the frequency of anti-neural antibody testing has increased over time. Additionally, population-based estimates of testing frequency and subsequent healthcare expenditures are scarce. 

Design/Methods:

Alberta, Canada has a centralized, publicly delivered healthcare system which is divided into discrete healthcare zones. The Calgary Zone provides healthcare to 1.5 million individuals, and nearly all autoantibody testing is performed by Mitogen Dx Laboratories (MDx). We obtained a comprehensive list of all AIE or paraneoplastic antibody tests performed in serum or cerebrospinal fluid (CSF) during a 3-year period spanning from Jan 1, 2018 to Dec 31, 2020 from MDx. We included individuals where the pattern of tested anti-neural antibodies suggested clinical suspicion for AIE. 

Results:

In total, 881 individuals had anti-neural antibody testing  for AIE in serum or CSF  (881/1,500,639 = 58.7/100,000 population) at a cost of $781,306 over 3 years. Mean costs were $260,435/year and $887/person. The number of individuals tested slightly increased over time (2018 = 293 individuals, 2019 = 304 individuals, 2020 = 317 individuals). In total, 821 (93.2%) individuals were tested for anti-NMDA, 794 (90.1%) for anti-VGKC (including anti-LGI-1 and anti-CASPR2), 574 (65.2%) for paraneoplastic antibodies and 63 (7.2%) for anti-IgLON5. At least one autoantibody resulted as positive for 64/881 (7.3%) individuals (4.3/100,000 population). Of 469 adults who were seen in an academic centre, 42/469 (9.0%) were positive, of which 10/469 (2.1%) were pathogenic. 

Conclusions:

Detection of pathogenic AIE anti-neural antibodies was rare despite high frequency and cost of testing. Frequency of testing marginally increased over 3 years.