Cyst of the conus medullaris manifesting amyotrophic lateral sclerosis syndrome.

An intramedullary cyst of the conus medullaris was found in a 49-year-old man, who presented progressive amyotrophy in the lower extremities, without root pain or sensory impairment. The clinical manifestation resembled that of ALS, although there were some atypical features, such as urinary difficulty and atrophy in the lower limbs. Myelography demonstrated an intradural oval mass and a laminectomy revealed a cystic malformation of the conus medullaris. Drainage of the cyst resulted in a marked clinical improvement.