103 Neurogenic Thoracic Outlet Syndrome

Case 103 Neurogenic Thoracic Outlet Syndrome

Stephen M. Russell

Clinical Presentation

A 32-year-old woman presents with a one-year history of left-hand weakness and incoordination, numbness in her medial left forearm, and paresthesias in her left fifth digit when she rotates her head to the right.
Her weakness temporarily worsens with overhead arm activity, including combing her hair and reaching for items.
She denies sensory symptoms in the thumb or first two fingers.
She is a slim woman with a long neck and poor posture.
On examination, she has mild atrophy and weakness in both the median and ulnar innervated hand intrinsic muscles compared with the opposite hand, hypesthesia along the medial left forearm, and a positive Tinel sign with gentle tapping in the left supraclavicular space.
Her radial pulse disappears in either arm when the arm is raised above her head.

Questions

What is your differential diagnosis?
Describe the myotome and dermatome for C8, T1, and the lower trunk.
What diagnostic studies would you request to help confirm the diagnosis?
What are the different types of thoracic outlet syndrome?
What is the proposed pathophysiology of neurogenic thoracic outlet syndrome?
What are the treatment options?
What is the success rate of surgery for neurogenic thoracic outlet syndrome?

Answers

What is your differential diagnosis?

Considering that her neurologic examination localizes her pathology to the lower trunk, the working diagnosis would be neurogenic thoracic outlet syndrome.

The differential diagnosis for neurogenic thoracic outlet includes cervical radiculopathy, carpal tunnel syndrome, ulnar nerve entrapment at the elbow, motor neuron disease, and a Pancoast tumor.1
Describe the myotome and dermatome for C8, T1, and the lower trunk.
- Together, C8 and T1 innervate all of the hand intrinsic musculature via both the ulnar and median nerves (they also provide contribution to some more proximal muscles).
- Figure 103.1 demonstrates the combined dermatome of C8 and T1, which represents the region of possible numbness or paresthesias in patients with neurogenic thoracic outlet syndrome.
- Classically, these patients have paresthesias and numbness along the medial forearm.
What diagnostic studies would you request to help confirm the diagnosis?
- An apical lordotic radiograph of the cervical spine should reveal any cervical ribs or “beaked” C7 transverse processes.
- Magnetic resonance imaging (MRI) with and without contrast of the brachial plexus (which should include the cervical spine) is ordered to exclude a herniated disc, foraminal stenosis, and tumors.
- Although frequently normal in mild cases, electrodiagnostic studies can reveal denervation in both ulnar and median innervated hand muscles (e.g., first dorsal interosseous and abductor pollicis brevis, respectively) and perhaps an absent nerve action potential from the medial antebrachial cutaneous nerve.
What are the different types of thoracic outlet syndrome?
- Thoracic outlet is categorized as neurogenic, vascular, or disputed.²
- Neurogenic and vascular thoracic outlet are both quite rare; the disputed type is much more common.
- Neurogenic thoracic outlet syndrome requires clear demonstration of objective neurologic finding on examination or diagnostic tests, including atrophy, electrodiagnostic testing abnormalities, a cervical rib, and/or focal nerve swelling on MRI.
- If no objective findings are present, the patient should be observed for their subsequent development.
What is the proposed pathophysiology of neurogenic thoracic outlet syndrome?
- Most experts believe that accessory ligaments and/or fascial bands related to a cervical rib or “beaked” C7 transverse process compress and distort the brachial plexus in patients with neurogenic thoracic outlet syndrome.³
- It remains controversial whether the anterior scalene, per se, is responsible for nerve entrapment.
What are the treatment options?
- For patients with mild symptoms and signs, posture training and a trial of physical therapy may lead to improvement.
- If atrophy and/or weakness are present, then surgical decompression of the brachial plexus is indicated.
- Once profound and chronic atrophy is present, however, the chance of surgical decompression causing a substantial improvement is unlikely.
- Therefore, early treatment is optimal.
- An anterior suprascapular exposure of the brachial plexus is the preferred approach by neurosurgeons in patients with neurogenic thoracic outlet syndrome (Fig. 103.2).⁴
What is the success rate of surgery for neurogenic thoracic outlet syndrome?
- If preoperatively the patient only has provocative symptoms (e.g., with overhead arm use), and only minimal signs of weakness and atrophy (i.e., mild cases), then surgical decompression leads to improvement in 85–90% of patients.
- When significant atrophy and weakness are present (moderate-to-severe cases), the chance of partial improvement is approximately two-thirds.⁵