Neuromyelitis optica spectrum disorders in South of Tunisia: A rare entity with low seroprevalence of anti-aquaporin 4 autoantibodies.

INTRODUCTION: Screening for anti-aquaporin 4 (anti-AQP4) antibodies, a specific marker of neuromyelitis optica spectrum disorders (NMOSD), is part of the immunological investigation performed in a context of central nervous system (CNS) inflammation with optic neuritis and/or myelitis. The aim of our study was to evaluate the prevalence and the diagnostic value of anti-AQP4 antibodies in Tunisian patients with such inflammatory neurological conditions. METHODS: During 3years, 170 consecutive serum samples of Tunisian patients with CNS inflammatory disorders and optico-spinal involvement were tested in our laboratory for anti-AQP4 antibodies using indirect immunofluorescence on transfected cells. RESULTS: The global seroprevalence of anti-AQP4 in our study was 4.1% (7 cases/170). The diagnosis of NMOSD was made for the 7 seropositive patients and for 2 seronegative patients, which leads to a seroprevalence of 77.7% in our NMOSD subgroup. The detection of anti-AQP4 allowed the diagnosis of NMOSD in 4 patients with incomplete clinical presentation and 5 patients with positive antinuclear antibodies. In one case, seropositivity was detected in a second sample, one year after an initial seronegativity. CONCLUSION: NMOSD seem to represent a rare etiology of optic neuritis and/or myelitis in Tunisian patients. Despite its low global seroprevalence in our study population, anti-AQP4 appears to be a very clinically relevant marker for NMOSD diagnosis. Repeating the screening in case of initial negativity could be interesting in clinical practice.