Neurogenic Thoracic Outlet Syndrome

Neurogenic thoracic outlet syndrome (NTOS) is a form of thoracic outlet syndrome (TOS; see this term) that presents with pain, paresthesias and weakness in an upper extremity and is divided into true NTOS and disputed NTOS.

Epidemiology

The incidence of NTOS is unknown. It affects women more than men. Disputed NTOS is the most controversial form and accounts for approximately 95% of all cases of TOS and 99% of cases with neurologic symptoms

Clinical description

NTOS presents with upper extremity paresthesias, pain and weakness. True NTOS manifests slowly with the progressive unilateral atrophic weakness of the intrinsic hand muscles and sensory abnormalities in a T1 distribution due to a lower trunk brachial plexopathy. Disputed NTOS does not cause muscle atrophy, but there is scalene muscle tenderness and symptoms worsen with arm use and provocative maneuvers.

Etiology

True NTOS is caused by lower trunk brachial plexus compression in the thoracic outlet at the interscalene triangle, costoclavicular space, or subcoracoid space deep to the pectoralis minor tendon. Disputed NTOS may be due to scarring of scalene muscles, poor posture or a congenital anomaly.

Diagnostic methods

Radiographs may identify compressive sources including an elongated C7 transverse process or anomalous first rib. Electrodiagnostic (EDX) findings demonstrate a lower trunk brachial plexopathy. MRI identifies compressive sources and rules out other causes such as a Pancoast tumor. Disputed NTOS is a clinical diagnosis that depends on scalene muscle tenderness and provocative maneuvers eliciting pain and paresthesias in the affected extremity as it lacks objective EDX evidence. It is most often a diagnosis of exclusion.

Differential diagnosis

Differential diagnoses include arterial and venous TOS (see these terms), cervical radiculopathy, carpal tunnel syndrome or any disorder involving nerve fibers derived from C8 or T1 nerve roots such as cubital tunnel syndrome. EDX testing differentiates the lower trunk brachial plexopathy of NTOS from other neurologic diagnoses. Arterial TOS presents with ischemia and venous TOS presents with venous congestion.

Management and treatment

Disputed NTOS is treated with physical therapy, medication and use of orthoses and neck collars. Refractory cases may undergo surgical decompression. For true NTOS surgical decompression is considered based on the degree of nerve injury and is indicated if there is acute or sub-acute progressive weakness or disabling pain and paresthesias.

Prognosis

In cases of true NTOS, decompression relieves pain, but full neurologic recovery requires time for remyelination or axonal regeneration. If there is axonal loss, recovery may be incomplete. Success rates for surgical decompression of disputed NTOS are 91%-93% immediately after treatment, but drop to 64% to 71% after 10 years due to a high rate of recurrence.