Cauda Equina Schwannoma

Cauda Equina Schwannoma Misdiagnosed as Focal Motor Neuron Disease
Bashar Katirji, MD, FACP

A 40-year-old man had a 4-year history of progressive right thigh weakness. Following a neurological consultation and normal magnetic resonance imaging (MRI) of the lumbar spine, the diagnosis of focal motor neuron disease was made. Recently, he required a kneeanklefoot orthosis for ambulation and experienced slight numbness of the right leg. He had no leg or back
pain. Examination showed severe atrophy with no power in the right quadriceps. Thigh adductors and hip flexors were severely weak (able to overcome gravity but no resistance). The right knee jerk was absent. There were no upper motor signs. Sensory examination showed patchy decreased pinprick and touch of the right leg.

Needle electromyography revealed fibrillation potentials and marked decrease of recruitment of motor unit action potentials (MUAPs) in the right quadriceps, thigh adductors, and iliacus muscles. In addition, there were scattered fibrillations and mildimpairment of MUAP recruitment in the right tibialis anterior,medial gastrocnemius and tibialis posterior, and the left quadriceps, thigh adductors, and iliacus. There were no fasciculation potentials and there were no fibrillation potentials in the lumbar paraspinal muscles. On nerve conduction studies, the right femoral motor response was absent and the left was normal, whereas the saphenous, sural, and superficial peroneal sensory responses were normal bilaterally. The electrodiagnostic findings were consistently severe right L3-L4 radiculopathies, but with additional mild right L5 and S1 and left L3-L4 radiculopathies.

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