To present 2 patients with recurrent atypical episodes of subacute worsening myelopathy, found to have spinal dural arterio-venous fistulas (SDAVF).

SDAVF are rare and frequently misdiagnosed due to their nonspecific symptomatology and delay of presentation on imaging. Spinal digital subtraction angiogram is the gold standard diagnostic test. Delayed diagnosis and treatment of SDAVF can lead to irreversible neurologic damage.

Two female patients, 69 and 74 years old, each developed recurrent episodes of subacute worsening myelopathy and urinary retention. The subacute onset of symptoms and longitudinal appearance on cord imaging raised concern for inflammatory myelitis. Despite a negative CSF analysis, and the absence of serum inflammatory, metabolic and infectious markers, the working diagnosis was seronegative neuromyelitis optica spectrum disorder. In accordance, both patients were treated with plasma exchange and IV rituximab, initially displaying stabilization on imaging. However, further worsening and extension of the myelopathy alongside the presence of flow voids in one patient's repeat MRI nine months post-presentation raised the question of an alternate etiology. A spinal angiogram was ordered for the patient, revealing SDAVF. Subsequently, the patient underwent complete Onyx embolization of the right L2 feeder and surgical clipping of the right L1 feeder. This resulted in stabilization and improvement of symptoms. Although the second patient did not display flow voids in their MRI, they were ordered a spinal angiogram due to their similar clinical course, indeed confirming SDAVF. The patient underwent successful complete embolization of the L3 segmental artery on the right resulting in improvement of symptoms. 

Clinicians should have a high index of suspicion for SDAVF when a patient presents with a longitudinally extensive transverse myelitis negative for inflammatory markers and is unresponsive to treatment. While the appearance of flow voids on imaging is a helpful diagnostic feature, these may not be present in patients.