Relationship Between Neuromyelitis Optica Spectrum Disorder and Sjögren's Syndrome: Central Nervous System Extraglandular Disease or Unrelated, Co‐Occurring Autoimmunity?

Objective Sjögren's syndrome (SS) patients may be affected by the neuromyelitis optica spectrum disorder (NMOSD), a severe demyelinating syndrome associated with anti–aquaporin 4 antibodies (anti‐AQP‐4 antibodies). The relationship between SS and NMOSD has been a sustained focus of investigation. Among SS patients, anti‐AQP‐4 antibodies have been detected exclusively in those with NMOSD. It has therefore been speculated that NMOSD is not a neurologic complication of SS. However, such studies evaluated small numbers of SS patients, often mixed with other inflammatory disorders. Methods We compared frequencies of anti‐AQP‐4 and SS‐associated antibodies in 109 SS patients, including 11 with NMOSD, 8 with non‐NMOSD demyelinating syndromes, and 90 without demyelinating syndromes. Results When assessed using a fluorescence‐activated cell sorting (FACS) assay, anti‐AQP‐4 antibodies were seen exclusively in those SS patients with NMOSD (72.7%), but not in SS patients without NMOSD (P