Sjögren Syndrome Associated Limbic Encephalitis and Its Longitudinal Brain FDG PET Manifestations

A 62-year-old woman with Sjögren syndrome, rheumatoid arthritis, and autoimmune hepatitis presented with subacute confusion and generalized seizures. MRI revealed bilateral mesial temporal T2/FLAIR hyperintensity. Serology revealed anti-SSA and anti-SSB antibodies elevated at 5 times above the upper limit of normal. FDG-PET demonstrated marked relative mesial temporal hypermetabolism with widespread hypometabolism in the rest of the brain; z-score mapping confirmed focal mesial temporal hyperactivity. They received immunotherapy and antiseizure therapy. After 1 year, cognition improved, though memory deficits persisted. Follow-up FDG-PET showed a transition from mesial temporal hypermetabolism to relative hypometabolism, with recovery of cortical metabolism, highlighting FDG-PET's role in diagnosing and monitoring autoimmune limbic encephalitis in Sjögren syndrome.