Broadening the Differential of Autoimmune Encephalitis: Diagnostic and Therapeutic Considerations in Down Syndrome Disintegrative Disorder

Objective To assess clinical features of Down Syndrome Disintegrative Disorder (DSDD) in trisomy 21 (T21) patients with a presumed diagnosis autoimmune encephalitis (AE) and analyze immunotherapy regimens timing. Background DSDD is characterized by acute to subacute developmental regression social functional skills emergence autistic behaviors T21. In contrast AE, brain imaging, cerebrospinal fluid (CSF) testing AE antibody panels are often unremarkable DSDD. However, anti-thyroid seropositivity the majority as well reported positive responses raise question an etiology. Design/Methods Retrospective analysis T21 progressive social, cognitive, and/or decline referred University Florida neuroimmunology clinic for establishment care suspected encephalitis. Results Two female were included onset autism, cognitive decline, insomnia, psychosis at 12 (P1) 16 (P2) years age. Catatonia was present one patient (P1). Diagnostic work-up pertinent antibody-seropositivity both cases (anti-microsomal peroxidase) oligoclonal bands (P2). Otherwise, MRI, EEG, CSF comprehensive serum/CSF negative. Both treated intravenous corticosteroids, immunoglobulins, additional immunosuppressive agents (azathioprine [P2]; plasmapheresis, rituximab, cyclophosphamide [P1]). Earlier initiation (9 months after symptom onset) associated partial sustained improvement while later (12 but non-sustained Conclusions align diagnostic had response immunotherapy. Sustained earlier initiation. should be consideration setting regression. Early considered better chance recovery.