By Michael Rubin, MD
Professor of Clinical Neurology, Weill Cornell Medical College
SYNOPSIS: The diagnosis of thoracic outlet syndrome may be difficult and relies on specific clinical, imaging, vascular, and electrodiagnostic features. None of the currently recommended treatments have been shown to be effective, but there are few randomized clinical treatment trials.
SOURCE: Mul K, Pesser N, Vervaart K, et al. Variability in electrodiagnostic findings associated with neurogenic thoracic outlet syndrome. Muscle Nerve 2021; Aug 11. doi: 10.1002/mus.27395. [Online ahead of print].
Thoracic outlet syndrome (TOS) is a controversial entity, and a confusing term, encompassing a group of neurological and vascular disorders related to compression of the neurovascular bundle above the first rib and behind the clavicle. This may give rise to a constellation of symptoms from arterial compression, from venous compression, and some from peripheral nerve compression.
Adding to the confusion, multiple terms have been applied to TOS, including cervical rib syndrome, costoclavicular syndrome, scalenus anticus syndrome, hyperabduction syndrome, subcoracoid-pectoralis minor syndrome, and Gilliatt-Sumner hand. True neurogenic TOS (NTOS) is diagnosed when clearly defined weakness and sensory loss in the arm and hand are present, resulting from an anomalous fibrous band or accessory cervical rib over which the lower trunk of the brachial plexus is angulated and stretched. What are the electrodiagnostic correlates associated with TOS?
Databases from tertiary referral clinics of the Neurology Department of the Radboud University Medical Center, Nijmegen, Netherlands, and the TOS-Expert Center of the Catharina Hospital, Eindhoven, Netherlands, were searched for patients diagnosed with NTOS between 2010 and 2021 who had undergone imaging of the thoracic outlet and electrodiagnostic studies (EMG). Inclusion criteria included symptoms or signs of lower cervical root or lower trunk brachial plexus involvement, imaging studies or intra-operative confirmation documenting compression of the lower plexus, and upper extremity EMG that were abnormal to any degree. Patients with a history of trauma or injury to the brachial plexus, or upper limb radiculopathy or mononeuropathy, were excluded. Brachial plexus imaging was performed using nerve ultrasound and/or magnetic resonance imaging, and NTOS was confirmed when enlargement of the lower trunk was documented.
Fourteen patients with NTOS fulfilled entry criteria, all of whom had lower brachial plexus compression documented and confirmed by imaging studies, and EMG which were abnormal. An axonal pattern consistent with T1 radiculopathy more than C8 nerve fiber involvement was present in seven patients, with the remainder having a variety of presentations, including C8 more than T1 involvement, equal involvement of C8 and T1, pure motor findings with normal sensory nerve action potential responses (SNAPs), needle EMG abnormalities limited to the flexor carpi radialis and biceps brachii muscles, and a single patient with an abnormal median SNAP from the third digit. Patterns of EMG abnormalities other than the “classic” T1 > C8 root pattern should not deter a diagnosis of TOS. High-resolution nerve imaging is a necessary complement in the evaluation of these patients.
COMMENTARY
TOS has a reported incidence of anywhere from three to 80 per 1,000 population and is more common between adolescence and middle age, particularly in females between 20 and 50 years of age. Treatment includes conservative measures as the first line, including physical therapy, lifestyle modification, and nonsteroidal anti-inflammatory agents. Botulinum toxin A injection of the anterior or middle scalene muscle, or of the scalene minimus muscle if present, has been suggested, but a randomized, double-blind, controlled trial demonstrated no improvement of pain or symptom reduction.
Paradoxically, the treated group experienced longer duration of symptoms than the control group, six vs. three years, respectively. Combined injection of steroids and local anesthetics have been beneficial, improving symptoms and overall function, with surgical decompression considered in the 30% to 40% in whom these measures fail.1
REFERENCE
- Li N, Dierks G, Vervaeke HE, et al. Thoracic outlet syndrome: A narrative review. J Clin Med 2021;10:962.
