The trident sign is a radiological finding on MRI classically described in neurosarcoidosis. The trident sign describes the appearance of central canal enhancement in addition to dorsal subpial enhancement on axial MRI of the spinal cord, giving the appearance of a trident or three-pronged spear. The trident sign has frequently been described with spinal cord involvement of neurosarcoidosis, but it has also been reported with other inflammatory causes of longitudinally extensive transverse myelitis including HTLV-1 infection and neuromyelitis optica spectrum disorder, as well as with diffuse large B-cell lymphoma.

A 67-year-old woman presented with 4 weeks of progressive, bilateral leg numbness and weakness. Brain MRI demonstrated speckled enhancement in the pons and middle cerebellar peduncles. Spine MRI demonstrated longitudinally extensive T2 hyperintensity with central and dorsal-subpial enhancement in a trident sign appearance. CSF showed 5 nucleated cells/uL (88% lymphocytes, 12% monocytes), 28 red blood cells/uL, glucose 63 mg/dL, and protein 130 mg/dL. CSF GFAP antibodies were positive at 1:32 on an otherwise negative myelopathy panel (Mayo) supporting diagnosis of GFAP astrocytopathy. Serum myelopathy panel (Mayo) and CSF cytokine panel (ARUP), flow cytometry, and cytology were unremarkable, as was whole-body FDG PET. She improved clinically with resolution of MRI abnormalities after intravenous methylprednisolone and plasma exchange. She has been stable for 12 months on maintenance rituximab.   

This case demonstrates that the trident sign is not specific to neurosarcoidosis and may be seen in other neuroinflammatory conditions. This case suggests a role for autoantibody testing in the evaluation of a patient with longitudinally extensive transverse myelitis with a trident sign pattern.