Lipoma causing a posterior interosseous nerve lesion.

A man aged sixty-two years complained of inability to extend his left index finger and thumb. This paralysis had been progressing for about twelve weeks, and had been accompanied by pain in the upper arm radiating into the forearm. On examination, there was paralysis of the extensor muscles of the left thumb and index finger. There were no sensory changes. In the extensor muscles, just distal to their origin from the humerus, there was an ill defined