To the Editor:

I read the review of the diagnosis and treatment of neuromyelitis optica spectrum disorder (NMOSD) by Gospe et al. with great interest [1]. The authors highlighted two important differences in the clinical presentation of NMOSD in children: low rates of AQP4-IgG seropositivity and high rates of acute disseminated enceophalomyelitis compared with optic neuritis or transverse myelitis. Paediatric NMOSD is rare, accounting for 3–5% of all NMOSD, however further key differences between paediatric and adult forms of the disease are important to recognise as they can alter clinical management [2].

As the authors state, AQP4-IgG seropositivity is rare in children with one study demonstrating 4% of children with NMOSD were seropositive and this low negative predictive value can contribute to diagnostic uncertainty [2]. MOG-IgG is positive in around 50% of cases and is therefore a more reliable biomarker [2]. In addition, whilst bilateral optic neuritis is characteristic in adult NMOSD the commonest cause of this presentation in children is post-infection [3]. Conversely, children are more likely to present with encephalopathy and endocrine dysfunction [2].

The radiographic features of NMOSD in children are also unique. Longitudinally extensive transverse myelitis (LETM) is typical in adults but is a poor predictor of paediatric NMOSD [3]. In one study it was shown that 0/9 children with LETM were AQP4-IgG positive [4]. The majority (67%) of children with NMOSD show brainstem and subcortical white matter lesions which are typically large and indistinct. Furthermore, over half (53%) of children show radiographic resolution which is rare in adults [2].

It is also worth recognising the differences in the treatment of NMOSD in children. The specifics of immunosuppression in children is outside the scope of this comment but are reviewed elsewhere [5]. However, it is important to consider the effects of corticosteroids on growth and the altered dosing and frequency of steroid sparing agents in children.

The majority of clinical treatment trials in NMOSD have focused on AQP4-IgG seropositive patients and thus neglect children who are typically seronegative. We should continue to consider the important differences between paediatric and adult NMOSD in both clinical practice and research.