A 50-year-old woman develops pain and parasthesia on the ulnar border of her left forearm and hand. On examination, her radial pulse is weaker on the left-hand side and her arm appears pale when elevated above her head.
- What is the most likely diagnosis?
This patient has symptoms and signs consistent with a diagnosis of thoracic outlet syndrome.
The brachial plexus and subclavian artery emerge through the superior thoracic aperture, which is a narrow space situated between the clavicle and the first rib, to enter the axilla. Confusingly, the superior thoracic aperture is also sometimes referred to as both the thoracic inlet and thoracic outlet.
Compression if either the artery, or the C8 and/or T1 nerves in this space, produces a clinical picture referred to as thoracic outlet syndrome. This syndrome has numerous causes, including the following:
- Cervical rib
- Enlarged C7 tranverse process
- Muscular abnormalities e.g. sickle-shaped scalenes medius
- Neck trauma
- Tumours e.g. Pancoast tumour (rare)
- Subclavian artery aneurysm (rare)
The clinical features of thoracic outlet syndrome are highly variable, but it usually presents with a gradual onset of neurological and/or vascular features:
- Weak radial pulse on affected side
- Blood pressure lower on affected side
- Limb pallor on elevation
- Unilateral Raynaud’s phenomenon
- Positive Adson’s sign (loss of radial pulse after rotation of the head to the ipsilateral side with neck extended following deep inspiration)
- Pain and/or parasethesia on ulnar border of hand and distal forearm
- May be sensory deficit present
- Often aggravated by exercise, particularly if arm raised
- Weakness and/or wasting corresponding to the part of the brachial plexus involved
- Frequently wasting of thenar muscles
- Interossei less commonly wasted
- Which investigations should be performed to confirm the diagnosis?
A cervical spine of chest X-ray may reveal the presence of a cervical rib or an enlarged tubercle anterior tubercle of C7. A chest X-ray may also be helpful in diagnosing a Pancoast tumour if that is the cause.
The investigation of choice for diagnosis is angiography. This can be with ultrasound, contrast-enhanced CT, MRI, or conventional angiography. Long-standing compression of the subclavian artery may result in a post-stenotic dilatation. Abduction and external rotation of the arm can cause complete obstruction of subclavian artery blood flow in cases caused by the presence of a cervical rib.
- How is this condition treated?
Neurological symptoms can often be treated conservatively with physiotherapy. Structural abnormalities should, however, be treated surgically if vascular and/or neurological problems are severe. There are numerous surgical options that depend upon the exact aetiology. A symptomatic cervical rib can be treated with scalenectomy and/or removal of the accessory rib. Occasionally a severely damaged section of the subclavian artery will require replacement with a graft.
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