Reflex sympathetic dystrophy associated with amyotrophic lateral sclerosis.

Reflex sympathetic dystrophy (RSD) is a syndrome characterised by severe distal pain and vasomotor changes. It is believed to be caused by sympathetic nervous system overactivity. Trauma is the most frequent precipitant event. An association with amyotrophic lateral sclerosis (ALS) has been reported only once. We report three patients with ALS in whom the occurrence of RSD, in one of them at a very early clinical stage, seemed to have precipitated a more rapid clinical evolution. New sprouting re-innervating fibres have abnormal ion channels which might increase the risk of RSD. On the other hand, motor changes have been described in RSD, as well as motor strength improvement after RSD treatment. The complex relation of ALS with RSD is discussed. In all ALS patients pain followed by further loss of function should prompt a search for RSD.