The H sign is a radiological sign appreciated on MRI spine that is classically described in patients with myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD).
The sign describes the involvement of spinal cord grey matter as seen on axial T2 sequences in patients with myelitis, whereby there is hyperintensity outlining the anterior and posterior horns 1-4. This gives the appearance to that of the letter 'H' 1-4.
The H sign is thought to be suggestive of myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD), being present in 29-63% of affected patients with myelitis 1,2. However, the sign is not pathognomonic, and may be also be present in approximately 30% of patients with seronegative myelitis. Notably, the H sign is present in less than 10% of patients with neuromyelitis optica spectrum disorder (NMOSD) and is not present in multiple sclerosis 1,2.
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