To highlight the importance of central canal and dorsal subpial enhancement - the trident sign - as a diagnostic clue for sarcoidosis isolated to the spinal cord through an illustrative case.

Isolated sarcoid myelopathy is challenging to distinguish from other inflammatory myelopathies. Biopsy of neural tissue remains the gold standard for identifying definitive neurosarcoidosis. The “trident sign” caused by enhancement of the central canal and dorsal subpial spinal cord has recently been described as strongly suggestive of underlying sarcoidosis. This sign may be particularly useful in cases of isolated sarcoid myelopathy where biopsy is too high risk and there is no other extraneural tissues to investigate.

Case report and review of the literature.

A 77-year-old woman presented for evaluation of subacute inflammatory myelopathy with marked impairement of proprioception, vibration, and light touch below C3 and a spastic gait. MRI of the brain and spinal cord with contrast showed a longitudinally extensive transverse myelitis extending from C2 to C7. No intracranial abnormalities were apparent on brain MRI. CSF demonstrated 3  oligoclonal bands, but was otherwise unremarkable. Aquaporin-4 cell-based assay was negative as were anti-MOG antibodies and a serum paraneoplastic panel. Her sensation and ambulation improved following a 3 day course of intravenous methylprednisolone but her symptoms worsened after a 1 week prednisone taper was completed.

A CT chest, abdomen, and pelvis did not show any evidence of lymphadenopathy. Spinal cord MRI revealed central canal and dorsal subpial enhancement as described by Zalewski et al as the “trident sign”. In the absence of a better explanation, given the abnormal MRI we diagnosed this patient as possible neurosarcoidosis. A higher dose prednisone regimen with azathioprine was recommended and she responded well with improvement of gait and sensation.  

This case demonstrates the utility of the “trident sign” as a tool to diagnose isolated sarcoid myelopathy.