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Myelin oligodendrocyte glycoprotein associated disease (MOGAD) is an acquired CNS demyelinating disorder with varied disease expression. While MOGAD has been known to cause longitudinally extensive transverse myelitis (LETM), the association with non-neurological comorbidities is not well reported.

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We report a case of a previously healthy 14-year-old male with subacute onset of bilateral lower extremity weakness. Neuroimaging revealed LETM extending from the cervical medullary junction to the conus medullaris with central gray matter T2 hyperintense edema and multiple subcortical T2 hyperintense lesions in the bilateral frontoparietal lobes. Within 24 hours of admission, he deteriorated from hemodynamically stable with adequate ventilation to pulseless ventricular tachycardia requiring 10 days of venoarterial extracorporeal membrane oxygenation. Examination revealed bilateral lower extremity paralysis with areflexia, urinary retention, sensory spinal level at T4 and ascending weakness, without associated encephalopathy. Serum MOG antibody titer was 1:100. Treatment included high dose methylprednisolone, plasmapheresis, intravenous immunoglobulin, and tocilizumab. Given the severity of the patient’s presentation, rapid whole genome sequencing was performed and revealed a pathogenic >200 CTG repeat expansion in DMPK, confirming a diagnosis of Myotonic Dystrophy type 1. One year after presentation, the patient can ambulate short distances without assistive devices, has improved bladder function without the need for catheterization, and has an insertable cardiac monitor without further evidence of atrial tachycardia. His one-year MRI showed residual spinal T2 hyperintensity without evidence of new lesions. He is maintained on tocilizimab 8mg/kg monthly.

This case highlights a rare and severe presentation of MOGAD-associated LETM complicated by cardiac arrest, ultimately revealing an underlying diagnosis of myotonic dystrophy type 1. It serves as a reminder that Occam’s Razor may not always apply, and underscores the importance of early recognition of rapidly progressive neurological deficits, prompt initiation of immunotherapy, and consideration of underlying genetic conditions in severe or atypical clinical courses.