Overlap syndrome of anti-aquaporin 4 positive neuromyelitis optica spectrum disorder and primary Sjögren's syndrome: a systematic review of individual patient data

Central nervous system (CNS) involvement can occur in primary Sjögren's syndrome (pSS) due to co-existing neuromyelitis optica spectrum disorder (NMOSD) which has a highly relapsing course requiring indefinite immunosuppression, and if not diagnosed early, damage accrual occurs over time leading to permanent disability and morbidity. In this review, we describe and outline the clinical course and outcomes of anti-aquaporin 4 (AQP4) antibody seropositive NMOSD with pSS overlap cases. To investigate the co-existence of AQP4 + NMOSD with pSS, we conducted a review of individual patient data from case reports and case series found in major databases. The study extracted clinico-demographic features, imaging and laboratory profiles, treatment approaches, and outcomes of these patients. Inclusion criteria for the review required patients to have positivity for anti-AQP4 or NMO-IgG autoantibodies in the blood and/or cerebrospinal fluid (CSF) and exhibit at least one manifestation of both pSS and NMOSD. In this overlap between AQP4 + NMOSD and pSS, 44 patients were included of whom 41 (93.2%) were females. The mean age of pSS onset was 44.8 ± 18.4 years and NMOSD onset was 43.2 ± 19.8 years. In 20 (45.5%) patients, NMOSD preceded pSS onset, 13 (29.5%) NMOSD occurred after pSS onset, and 11 (25%) patients had a simultaneous presentation. 31 (70.5%) patients experienced acute transverse myelitis, 21 (47.7%) optic neuritis, 14 (31.8%) cerebral syndrome, 10 (22.7%) acute brainstem syndrome, 5 (11.4%) area postrema syndrome, and 2 (4.5%) diencephalic clinical syndromes. For the treatment of acute phase, 40 (90.9%) patients received intravenous methylprednisolone, 15 (34.1%) received plasma exchange, and 10 (22.7%) received intravenous immunoglobulin; and for the induction/maintenance therapy, 16 (36.4%) patients received cyclophosphamide, 6 (13.6%) received rituximab, 16 (36.4%) received azathioprine, and 10 (22.7%) received mycophenolate mofetil. Disease course was monophasic in 2 (4.5%) and relapsing in 27 (61.4%) patients. At median (IQR) follow-up duration of 2.4 (6) years, 39 (88.6%) patients showed improvement, 3 (6.8%) showed stabilization and 2 (4.5%) showed worsening of their NMOSD manifestations. In this overlap syndrome of AQP4 + NMOSD and pSS, patients have a neurologically disabling disorder that can mimic neurological manifestations of pSS, frequently occurs prior to the onset of pSS, has a relapsing course, responds well to immunosuppressants, and necessitates indefinite treatment. Collaborative multicentre studies are needed to clarify the natural history and outcomes of this rare overlap syndrome.