The interval between attacks can vary widely, lasting months or even years; however, the relapsing course may lead to functional impairments, with more than a fifth of patients requiring gait assistance within five years.^1,4

Relapse is defined as the onset of new or worsening of original symptoms, with a duration of more than 24 hours, in the absence of other recognised causes such as fever and infection.^*7

The effects of NMOSD relapses include vision loss, pain and paralysis.^4,5 Almost half of patients with NMOSD can experience one or more relapses, resulting in hospital/inpatient admissions and ambulatory/outpatient treatments within 2 years.⁸

Following an NMOSD attack, many patients do not fully recover and there is an increased risk of essential function loss with subsequent attacks.²

76% of patients experience only partial or no recovery from myelitis after the first attack.^†2

* Some studies further defined relapse as an increase of at least 0.5 on the extended disability status scale (EDSS), an increase of at least 1 on two functional system (FS) scales, or an increase of at least 2 on one FS scale.⁷

^† (n = 93/123).²

* A retrospective study of 175 patients of whom 156 (89.1%) were relapsing and 137 (78.3%) were AQP4 positive.²