Mimicking Amyotrophic Lateral Sclerosis: A Case of a Spinal Dural Arteriovenous Fistula

A number of conditions can mimic amyotrophic lateral sclerosis (ALS), which are in general excluded by neurophysiological and neuroimaging investigation. We present a novel mimicking disorder. A 58-year-old male, without relevant past medical history, presented with a 7-year history of progressive paraparesis. On examination, he had bilateral thigh atrophy, fasciculations, and asymmetric paraparesis (severe on the left side). Upper motor neuron signs were present in the lower limbs, with normal sensory examination. Needle EMG disclosed mild chronic neurogenic changes in the lower limbs. Brain and spinal cord neuroimaging was normal, namely, in the dorso-lumbar segment. Lumbar puncture showed mild hyperproteinorachia. Diagnosis of slowly progressive (possible) ALS was established. One year later, he required a bilateral support to walk, and neurological examination revealed weak tendon reflexes, abnormal pinprick, and proprioceptive sensation in the legs. Repeated lumbar MRI showed an extensive spinal cord oedema from T7 to the conus with multiple perimedullary vessel flow voids suggestive of a vascular malformation. Conventional angiography revealed a spinal dural arteriovenous fistula in L2-L3 with the left L4 lumbar branch as the afferent artery. Dural arteriovenous fistula is the most common vascular malformation of the spinal cord, despite being rare. It leads to arterialization of spinal veins, causing venous hypertension, spinal cord oedema, and ischaemia. The clinical picture includes a stepwise, sometimes fluctuant, myeloradiculopathy. In this case, EMG changes did not meet Awaji criteria. This case reinforces the need to critically follow atypical cases to ascertain clinical progression in patients with suspected ALS.