[Cyst of the conus masquerading as motor neuron disease].

We report on a patient presenting with rapidly progressive painless paraplegia, amyotrophy and fasciculations masquerading as motoneuron disease. There were no bowel or bladder involvement but the patient noted mild paresthesia on the external part of the right foot and hypertrophy of the right calve was present. While lumbar CT Scan was normal, MRI showed a large cyst of the conus. Analysis of the cyst concluded to a benign cyst of the conus. Paraplegia resolved after surgery and after one year, no relapse was observed so that an hidden ependymoma appeared unlikely.