Neuromyelitis optica spectrum disorder with increased aquaporin-4 microparticles prior to autoantibodies in cerebrospinal fluid: a case report

Background: Neuromyelitis optica spectrum disorders are severe autoimmune inflammatory diseases of the central nervous system associated with the presence of immunoglobulin G antibodies against the water channel protein aquaporin-4. During exacerbation, specific aquaporin-4 immunoglobulin G may be produced intrathecally. We measured extracellular aquaporin-4 microparticles in the cerebrospinal fluid of a patient who later developed the typical symptoms and signs of a neuromyelitis optica spectrum disorder.

Case presentation: A 17-year-old South American girl developed acute severe motor and vocal tics and difficulties in walking, peripheral numbness, muscle pain, and bilateral headache. At age 22, she had a multitude of motor and psychiatric symptoms. Over the years, she fulfilled the diagnostic criteria for anorexia nervosa, depression, sleep disorder, obsessive-compulsive disorder, generalized anxiety disorder, panic disorder, agoraphobia, social anxiety disorder, development coordination disorder, attention-deficit/hyperactivity disorder, hypomania, pediatric autoimmune neuropsychiatric disorders associated with streptococcal infections, conversion disorder, psychosis, and schizotypal personality syndrome. At age 24, she was found to have elevated titers of aquaporin-4 antibodies in serum, suggestive of probable neuromyelitis optica. She subsequently developed visual impairment, and swollen optic nerves were verified by magnetic resonance imaging. She was thus treated with a chimeric monoclonal antibody targeted against the pan-B-cell marker CD20 (rituximab), and almost all symptoms, including the psychiatric symptoms, rapidly decreased. We found a significant increase of extracellular microparticles of aquaporin-4 in cerebrospinal fluid sampled from our patient when she was 22 years old, 2 years before the full clinical development of neuromyelitis optica.

Conclusions: Microparticles of aquaporin-4 represent subcellular arrangements that may influence the pathogenesis of neuromyelitis optica spectrum disorders and may serve as biomarkers for the underlying cellular disturbances. The increase of aquaporin-4 microparticles in cerebrospinal fluid may be used for early diagnostic purposes; for prevention; and for evaluation of effective treatment, long-term follow-up studies, and elucidating the pathophysiology in neuromyelitis optica spectrum disorders. Further studies of aquaporin-4 microparticles in cerebrospinal fluid of patients with neuromyelitis optica and similar neuropsychiatric disorders are thus called for.