[True neurogenic outlet syndrome: report of 2 cases].

True neurogenic thoracic outlet syndrome is caused by compression of the lower trunk of the brachial plexus usually by a cervical rib, fibrous band or an elongated transverse process of C7. We describe two cases of female patients (23 and 19 years old) with pain in the right superior limb and progressive muscular weakness and atrophy of the intrinsic muscles of hand. Electrodiagnostic studies showed reduced amplitude of compound muscle action potential of median nerve and decreased amplitude of ulnar sensory nerve action potential. Motor and sensory nerve conduction velocities were normal in both patients. Needle electromyography were findings compatible with chronic denervation in the intrinsic muscles of the right hand of both patients. Radiological investigation showed cervical ribs in one case and elongated transverse process of C7 in the other. A discussion about the clinical and electrophysiological features and the treatment of the syndrome was performed.