Superficial Siderosis Should Be Included in the Differential Diagnosis of Motor Neuron Disease

Abstract

Recent studies have revealed that some patients with superficial siderosis (SS) show evidence of an intraspinal fluid-filled collection on imaging. Some of these patients also show clinical and/or imaging features of craniospinal hypovolemia related to dural defects. We report a patient with SS whose clinical presentation was suggestive of motor neuron disease and whose history was remarkable for cerebrospinal fluid (CSF) hypovolemia. This report also reviews the literature on the relationship between SS, dural defects, and CSF hypovolemia. A 58-year-old left-handed man was evaluated for an 18-month history of progressive imbalance with limb muscle weakness, wasting, and fasciculations. Brain magnetic resonance imaging (MRI) studies were remarkable for evidence of SS and diffuse pachymeningeal enhancement similar to that seen in craniospinal hypovolemia. Spine MRI showed a longitudinal intraspinal fluid-filled collection. A dynamic computed tomographic myelogram of the spine showed a CSF leak adjacent to a peripherally calcified disk at the T2-3 level. Following repair of the dural defect the patient noted an improvement in balance and strength and resolution of the fasciculations. A cervical and thoracic spine MRI showed resolution of the intraspinal fluid-filled collection, and a CSF study showed no red blood cells or xanthochromia. The clinical spectrum of disorders related to dural defects includes craniospinal hypovolemia, SS-related ataxia and impaired hearing, segmental weakness and atrophy with or without hyperreflexia, and spinal cord herniation. The clinical features of these conditions may overlap. Longitudinally extensive ventral dissecting meningoceles can be seen in all these conditions. A dynamic computed tomographic myelogram can identify a dural defect. In some cases the dural defect may result from an osteophyte.