From the Guidelines
The best test to confirm Thoracic Outlet Syndrome (TOS) is Magnetic Resonance Imaging (MRI) of the thoracic outlet, as it can visualize both vascular and neurological structures while the patient performs maneuvers that provoke symptoms. This is based on the most recent and highest quality study available, which suggests that MRI has inherent advantages over other imaging modalities in its ability to delineate extravascular anatomy and characterize soft tissues 1.
Key Points to Consider
- MRI can define the brachial plexus and cervical spine, and dynamic evaluation of neurovascular bundles in the costoclavicular, interscalene, and pectoralis minor spaces are required for evaluation of patients with nTOS 1.
- Noncontrast MRI can be sufficient to diagnose nTOS, and MRI without IV contrast may also be performed in the postintervention setting to evaluate interval changes in the thoracic outlet and assess adequate decompression 1.
- Other imaging modalities, such as CT chest, CTA chest, and CTV chest, may not provide further evaluation of the neurologic structures as compared with chest CT, and are not considered first-line tests for nTOS pre- or postoperatively 1.
Clinical Considerations
- Initial evaluation should include provocative clinical maneuvers, such as Adson's test, Wright's test, and the elevated arm stress test (EAST), which reproduce symptoms by compressing the neurovascular structures in the thoracic outlet.
- Diagnostic imaging should be pursued if these tests suggest TOS, and MRI or MRA of the thoracic outlet is preferred as it can visualize both vascular and neurological structures while the patient performs maneuvers that provoke symptoms.
- Electromyography and nerve conduction studies are useful for neurogenic TOS to document nerve compression, and in some cases, diagnostic lidocaine injection into the anterior scalene muscle may be performed; symptom relief suggests neurogenic TOS 1.
From the Research
Diagnostic Tests for Thoracic Outlet Syndrome (TOS)
The diagnosis of TOS is based on a holistic approach that includes clinical features, physical examination findings, electromyography, nerve conduction studies, and imaging 2, 3, 4.
Imaging Tests
- MRI and MR angiography are useful in confirming the diagnosis, excluding mimics, and classifying TOS into neurogenic, arterial, venous, or mixed causes 2.
- Computed tomography angiography (CTA) can detect structural abnormalities, such as focal stenosis of the subclavian artery 3.
- MRI can assess anatomy and abnormalities, vessel assessment, and dynamic compression of vessels with abduction of the arms 2.
Electrodiagnostic Tests
- Nerve conduction study (NCS) and needle electromyography (EMG) can help diagnose TOS, particularly in true neurogenic TOS 3.
- Medial antebrachial cutaneous (MABC) sensory nerve action potential amplitude is decreased in patients with true neurogenic TOS 3.
Limitations of Diagnostic Tests
- The sensitivity and specificity of MRI in diagnosing TOS are low, with a sensitivity of 41% and specificity of 33% 5.
- Diagnosis should be based on a holistic approach, including history, clinical examination, and radiological findings 5.
Best Test to Confirm TOS
There is no single best test to confirm TOS, as diagnosis is based on a combination of clinical features, physical examination findings, electromyography, nerve conduction studies, and imaging 2, 3, 4. A complete MRI examination, including assessment of anatomy and abnormalities, vessel assessment, and dynamic compression of vessels, can be useful in confirming the diagnosis and classifying TOS 2. However, the low sensitivity and specificity of MRI highlight the importance of a holistic approach to diagnosis 5.