Cerebellar Involvement in Attacks of Aquaporin-4-IgG Positive Neuromyelitis Optica Spectrum Disorder

Objectives: To characterize the frequency and clinicoradiologic phenotype of cerebellar involvement in attacks of aquaporin-4-IgG positive neuromyelitis optica spectrum disorder (AQP4+NMOSD) which are incompletely captured in current diagnostic criteria. Methods: Brain MRI scans from patients with AQP4+NMOSD in the Mayo Clinic database were reviewed, and those with cerebellar T2-hyperintense lesions ≤30 days from attack onset were included for clinical and radiologic characterization. Results: From 432 patients with AQP4+NMOSD, we identified 17 (4%) with cerebellar attacks. The median age at attack onset was 47 years (range, 7-74). Cerebellar symptoms and signs were noted in 16 (94%) of 17 and the remaining patient was intubated preventing a detailed cerebellar exam. The median Expanded Disability Status Scale score at nadir was 5 (range, 2-9.5). Sixteen (94%) had other regions involved during the attack, most frequently with brainstem or area postrema involvement. Cerebellar MRI T2-lesions (8 single; 11 contiguous with the brainstem; 6/15 [35%] enhancing) were located in cerebellar peduncles, 15 (inferior, 5; middle, 10; superior, 10), and cerebellar parenchyma, 8 (dentate, 4; medial, 2; lateral, 4). T2-lesions persisted in 9 (82%) of 11 beyond 6 months. Discussion: Cerebellar involvement during attacks of AQP4+NMOSD is rare but the associated neurologic deficits tend to be severe. Cerebellar peduncle or dentate nucleus T2-lesions are frequent MRI accompaniments. Clinical features and MRI lesion patterns of cerebellar involvement could be incorporated into future iterations of AQP4+NMOSD criteria.