Anti-dipeptidyl-peptidase-like protein 6 encephalitis, a rare cause of reversible rapid progressive dementia and insomnia.

Anti-dipeptidyl-peptidase-like protein 6 (DPPX) encephalitis is a rare type of autoimmune encephalitis. We present a case of a 72-year-old male with anti-DPPX encephalitis who developed rapidly progressive cognitive decline, psychiatric and sleep problems, severe abdominal pain and diarrhea. Antibodies against DPPX were positive both in serum and cerebrospinal fluid. ¹⁸F-FDG PET-MR imaging indicated hypometabolism in the bilateral temporal lobes and thalamus. No related tumors were found, and the patient responded to immunotherapy without relapse at the 3-year follow-up. The present case enriches the understanding of the clinical, imaging manifestations and prognosis of anti-DPPX encephalitis.