Background: Spinal dural arteriovenous fistula (SDAVF) is a known cause of nontraumatic slow progressive araparesia and is frequently overlooked because its clinical features overlap with more common causes of myelopathy and also neuroimaging may be normal.

Case Report: A 53 year-old man with developed weakness of both lower limbs had symptoms begun spontaneously 3.5 month before admission and progressed from 1 month ago with bowel and bladder incontinence. The patient's physical examination was normal and neurologic testing revealed lower extremity motor strength of 3/5. Deep tendon reflexes were decreased and superficial abdominal reflexes were absent. Sensation of pinprick and temperature was absent distal to the T4-T5 level. Vibration and proprioception were decreased to the ankle and saddle anesthesia and the patient was non ambulatory. Laboratory routine and specific tests for vitamin B12 level, hepatitis, HIV, HTLV_{1, 2} were negative. MRI of spine with and without contrast raised the possibility of dural arteriovenous malformation extended from T3 level to conus medullaris which was confirmed by angiography. The patient referred to neurosurgeon for deciding route of treatment.

Conclusion: SDAVF can be a significant non traumatic slowly progressive cause of myelopathy. The majority of the affected patients are males older than 50 years of age. Rapid diagnosis in these patients leads to significant improvement.