True neurologic thoracic outlet syndrome -: Anatomical features and electrophysiological long-term follow-up of lateral thenar atrophy

Atrophies of the intrinsic muscles of the hand are considered to be a typical symptom of the "true neurologic" form of thoracic outlet syndrome (TOS). The classical form of this entity was described as early as 1970, consisting of a cervical rib or a prolonged transverse process of C7, complete with a fibrous band to the first thoracic rib, resulting in atrophy of the intrinsic muscles of the hand. All our TOS patients presenting with such atrophy displayed anatomical findings consistent with this definition. Based on this observation, the TOS classification currently in clinical use, which differentiates between "disputed" and "true neurologic" subgroups of the neurologic form, is reviewed. In all cases of "true neurologic TOS" with atrophy of the intrinsic muscles of the hand, the lateral thenar muscles are affected first. We present the electrophysiological long-term results of such thenar atrophies of seven patients with eight operated extremities after brachial plexus decompression. The amplitude of the neurographically measured potential over the opponens pollicis and the abductor pollicis brevis muscle, respectively, was defined as quantitative parameter for muscles atrophy. Neither distinct reinnervation nor progressive denervation was evident in any of the cases after a follow-up period, on average, of more than five years post surgery. These findings are in conflict with clinical observations reporting a majoritarian postoperative improvement of the motor deficits.