Somatosensory evoked responses in the diagnosis of thoracic outlet syndrome.

Abstract

SUMMARY A study was made of 11 patients with cervical rib, and one patient with Klippel-Fiel syndrome and enlarged transverse processes to determine whether evoked potentials recorded from both Erb's points and the cervical spine in response to median and ulnar nerve stimulation provided information additional to that obtained by EMG and peripheral conduction studies. It was found that in seven patients who had pain and paraesthesias but no objective neurological signs both the peripheral and central conduction studies were within normal limits. By contrast, of five patients who had objective signs, conventional EMG and conduction studies were abnormal in three patients, but abnormalities of the evoked potentials obtained from ulnar nerve stimulation were obtained in all five patients. It is suggested that this application of evoked potential estimation is a useful addition to the more conventional peripheral investigations.The thoracic outlet syndrome is charactensed by a combination of pain in the arm provoked by traction, colour changes in the hand, and a radicular pattern of sensory loss and weakness with intact tendon reflexes. The incidence of thoracic outlet syndrome is uncertain, and the diagnostic criteria are disputed. The abnormalities in motor and sensory conduction in the peripheral segments of the median and ulnar nerves in patients with cervical ribs or bands have been well described by Gilliatt et all and Wulff and Gilliatt.2 Shahani et a13 Dorfman,4 and Eisen et al5 have studied the use of F wave latency in the diagnosis of thoracic outlet syndrome.The major abnormalities described in these studies were reduction in amplitudes of the ulnar sensory action potentials, chronic partial denervation in the intrinsic muscles of the involved hand (C8-T1) and prolongation of the F wave latency.However, in some patients with wasted hands the nerve conduction studies were normal and if there were no associated objective signs the diagnostic yield from electrophysiological studies was low.

True neurogenic thoracic outlet syndrome: Electrophysiological diagnosis in six cases

“…12 The use of somatosensory evoked potentials for diagnostic purposes has also been questioned. 14,22 Our 6 patients had clinical features typical of true neurogenic TOS. All were female and presented marked atrophy of the thenar muscles.…”

AAEM minimonograph 19: Somatosensory evoked potentials

“…The SEP findings in such patients are variable. Both the authors' findings, 6 and those reported from the Mayo Clinic, 120 indicate that SEP studies are of limited value for the diagnosis of the neurogenic variety of thoracic outlet syndrome. In some patients there may be abnormalities of the ulnar-derived SEP, such as an absent or markedly attenuated N13 response despite a relatively normal N9 peak, or a small delayed N9 peak with or without abnormalities of the N13 or N20 or prolonged interpeak intervals.…”

“…6 In patients with the nonneurogenic syndrome, the authors and others have found normal median, ulnar, or radial SEPs. 6,68,120 However, in one study, 12 of 18 patients, most of whom had no clinical deficit, were found to have abnormal ulnar SEPs, with small N9 potentials despite preserved distal ulnar SNAPs, a finding difficult to explain on pathophysiologic grounds. 59 In another study, 13 of 19 patients with suspected thoracic outlet syndrome had abnormal SEPs evoked by median or ulnar nerve stimulation, 48 but the clinical and electrophysiologic findings were not detailed, and interpretation is further complicated because diagnostic criteria for the SEP abnormalities were not provided.…”

16.7 Thoracic-Outlet-Syndrom (TOS)

“…Andere Autoren bestätigten diese Befunde, fanden allerdings, dass eine FWellenLatenzverlängerung in der Regel erst bei fortgeschrittenen, neurogenen Veränderungen (Atrophien) nachgewie sen werden kann (Cakmur et al 1998 (Aminoff et al 1988). In der klini schen Routine sind die SSEP von geringer Aussagekraft für die Diagnose eines neurogenen TOS und bringen auch keine neuen Aspekte in der Diagnostik der nicht neurogenen TOSVariante (Yannikas et al 1983;Komanetsky et al 1996;Aminoff und Eisen 1998). Obschon SSEP in der direkten Diagnostik des NTOS keine wesentliche Rolle spielen, können sie zur Differenzialdiagnose anderer Erkrankungen, wie beispielsweise demyelinisierende Erkrankungen des Zent ralnervensystems oder stenosierende zervikale Myelopathien, relevante Infor mationen liefern.…”