AQP4 and erythema multiforme: Infections also frequently precede relapses in both NMOSD and MOG-EM/MOGAD; taking into account both the first attack and subsequent attacks, NMOSD attacks were preceded by infections in around 30% of AQP4-IgG-positive and 20% of AQP4-IgG-negative cases in a large European study [87].