(102) Positive Antibodies in Atypical Dementia: A Case Report Exploring the Intricacies of Diagnosing Rapid Cognitive Decline

Background/Significance: Autoimmune encephalitis (AIE) can be extremely difficult to differentiate from general dementia syndromes and often results in a time-intensive and costly diagnostic dilemma.

Case Description: A 70-year-old woman with PMH of atrial fibrillation, thyroid disease, and recent illness with Covid-19 was brought in by her husband for weeks of worsening mental status, personality change, severe agitation and rapid cognitive decline. Her initial workup discovered a large mediastinal mass and positive serum antibody test (anti-alpha 3 AChR) on the auto-immune encephalitis antibody panel. Her symptoms continued to worsen, resulting in presentation at our hospital weeks later with psychosis and mania. Workup for strongly suspected AIE was initiated, including lumbar puncture with Mayo Clinic Encephalopathy Paraneoplastic/Autoimmune CSF panel, serum studies, pan-CT, brain MRI with and without contrast, and alternate causes workup including infectious, thyroid, toxicities, and vitamin deficiencies. The patient was immediately started on high-dose methylprednisolone for empiric treatment of AIE. The CL Psychiatry team was consulted for severe agitation management requiring restraints. The patient had paranoid and grandiose delusions, severe cognitive impairment, and delirium, and her MoCA Test was 17/30. She was placed on valproic acid, lorazepam at bedtime. Patient was then started on intravenous immune globulin (IVIG) but still had minimal improvement in symptoms. Three weeks later, the send-out panel returned, but her CSF was negative for any autoimmune antibodies for AIE. Her mediastinal mass was ultimately thought to be a large goiter that had been present for over 15 years, and family declined a biopsy. Due to the lack of clear laboratory evidence for AIE and lack of empiric treatment response, the patient was diagnosed with atypical dementia.

Discussion: Multiple factors initially contributed to the strong consideration of autoimmune encephalitis as the cause of rapid onset of psychiatric symptoms and behavioral change in this 70 year old previously healthy female. They include patient-specific factors, including the presence of autoantibodies on the serum panel and atypical rapid decline, historical factors such as limited collateral, and systemic factors such as a fragmented healthcare system and delay in encephalitis panel results. Differentiating between organic and unidentifiable causes of dementia can be difficult and even disappointing for patients/families to accept.

Conclusion/Implications: There have been numerous case reports describing how AIE can mimic dementia, but this case provides an example of presumed AIE that was eventually excluded in favor of an atypical dementia syndrome. Ultimately, the presence of red flags for AIE warrants a thorough investigation, but it may be difficult for clinicians to reject anchoring bias if the workup comes back negative. Additionally, empiric treatment for AIE can further complicate the presentation but should not be delayed.

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