To expand the known phenotypic spectrum of pediatric cerebral MOGAD.

Cerebellar mutism is well described in the context of posterior fossa syndrome following surgical resection of pediatric cerebellar tumors. Cerebellar mutism can also occur in the setting of parainfectious and inflammatory cerebellitis, but this phenomenon has not specifically been characterized as a consequence of pediatric cerebral MOGAD.

Retrospective descriptive review of a single case. Longitudinal neurological and cognitive recovery are described using modified Rankin scale (MRS), coma recovery scale-revised (CRS-R), and cognitive and linguistic scale (CALS). 

A previously healthy 11 year old girl presented with rapidly progressive ataxia and mutism in the setting of febrile illness (influenza A positive). EEG showed normal background activity. MRI revealed acute cytotoxic edema (hyperintensity on diffusion weighted imaging and T2 sequence, hypointensity on apparent diffusion coefficient) of bilateral cerebellar hemispheres symmetrically, with mass effect and cerebellar leptomeningeal enhancement. CSF confirmed neutrophilic pleocytosis (WBC 83, 95% neutrophils), negative oligoclonal banding, and negative infectious testing. Serum MOG IgG was ultimately positive (titer 1:20, cell based assay, Mayo Clinic Laboratories) confirming diagnosis of MOGAD. She was treated with high dose methylprednisolone, intravenous immunoglobulin, and therapeutic plasma exchange, with improvement in truncal ataxia and resolution of radiographic edema/enhancement, but remained completely mute/anarthric. Given persistent elevation in serum interleukin 6, she subsequently received escalation treatment with tocilizumab. Despite aggressive immunotherapy and intensive inpatient rehabilitation, she remained non-verbal 60 days from onset: MRS was 5 (severe disability), CRS-R was 15 (minimally conscious state), and CALS was 45 (min-max range is 20-100, indicating ongoing severe deficits).

Cerebellar mutism can manifest in children with MOGAD and cerebellitis. Language and cognitive deficits can be profound and refractory to immune therapy, despite improvement in ataxia and radiographic edema.