The presence of symptoms depends on collateralization. Upper limb symptoms comprise arm claudication or muscle fatigue, rest pain and finger necrosis from embolic debris. Characteristic neurologic symptoms include vertebrobasilar hypoperfusion including visual abnormalities (diplopia), drop attacks, syncope, ataxia, vertigo, dysphasia, dysarthria, dizziness, nystagmus, tinnitus, hearing loss, and facial sensory deficits. Vertebrobasilar insufficiency develops when subclavian artery thrombosis is distal to the origin of the vertebral artery; thus, during conditions of increased flow distal to the stenosis like exercise, results in retrograde flow in the vertebral artery, followed by decreased flow in the basilar artery.

One of the rare complications of subclavian stenosis develops in a patient who has had coronary artery bypass surgery with the internal mammary artery (IMA) graft is angina pectoris. The internal mammary artery arises from the subclavian artery and can be affected by stenosis. If there is subclavian artery thrombosis proximal to the IMA graft, flow impairment to the IMA may occur. In instances of severe stenosis, retrograde flow from the grafted coronary artery to the brachial artery may lead to angina; a phenomenon called coronary steal syndrome.

Physical examination particularly cardiovascular examination may reveal unequal blood pressure in arms, absent or diminished pulses (axillary, brachial and radial/ulnar) compared to the contralateral arm, and cervical or supraclavicular bruits. Ischemic findings such as gangrenous skin changes of the fingers or splinter hemorrhages of the nail bed may also present. The examination should also focus on the cerebral circulation including palpation of carotid pulses and auscultation for vertebral (suboccipital region) and carotid bruits.

The inter-arm systolic blood pressure difference of less than 10mm Hg has a negative predictive value of 99%.[5] 

The goal standard diagnostic modality is imaging.  However, diagnosis is possible from clinical findings which may suggest possible subclavian artery thrombosis, including unequal upper limb blood pressures, absent or diminished axillary, brachial, radial or ulnar pulses, and digital ulceration or gangrene. 

The difference of systolic blood pressure of over 10 mm Hg between both the arms has a positive predictive value of 13%.[5] However, if the systolic cut-off increases to 15 or 20 mm Hg, positive predictive value increases to 67% to 100% and negative predictive value up to 100%.[10][11]

Non-invasive diagnostic imaging for the diagnosis of subclavian artery thrombosis is duplex ultrasound with color flow. Duplex ultrasonography shows waveform dampening or monophasic changes, color aliasing suggestive of turbulent flow, and increased blood flow velocities at the location of the stenosis. Doppler ultrasonography can also diagnose a reversal of ipsilateral vertebral artery flow as seen in subclavian steal syndrome. 

More accurate diagnostic modalities include computed tomography angiography and magnetic resonance angiography, reserved for when intervention is mandatory.

The recommendations for screening include when a patient is undergoing coronary artery revascularization using the intermammary artery such as CABG, and the suspicion of subclavian stenosis is high, or if a patient has a history of peripheral artery disease or systolic blood pressure differences in their upper limbs of over 10 mm Hg.[12]

Indications for the treatment are as follows;

1. Morbid upper arm ischemia (57%)
2. Upper limb claudication
3. Upper extremity pain at rest
4. Fingers embolization
5. Vertebrobasilar insufficiency from steal syndrome (37%)
6. Anginal symptoms from coronary steal via Intermammary artery graft (21%)
7. Leg claudication in the presence of axillofemoral graft

Medical therapy includes antiplatelet including aspirin or clopidogrel, HMG-CoA reductase inhibitors, and either angiotensin-converting enzyme (ACE) inhibitors or angiotensin receptor blockers. The patient counseled against smoking, and if diabetes is present, strict glycemic control is advisable with the target HbA1c of less than 7.[4]

Surgical treatment is sometimes necessary. In 1951, Shimizu and Sano first reported surgical repair of subclavian artery thrombosis.[13] The different options to correct subclavian artery pathology include:

• Axillary–axillary bypass
• Carotid-subclavian bypass
• Transposition of the subclavian artery

The axillary–axillary bypass surgery has a good prognosis in terms of morbidity and mortality.[14]

Endovascular intervention is the best modality currently for relieving subclavian artery thrombosis including percutaneous transluminal angioplasty with stenting or ballooning.[15]

• Congenital malformations
• Fibromuscular dysplasia
• Neurofibromatosis
• Autoimmune vasculitis like Takayasu
• Radiation exposure
• Mechanical causes like trauma or compression syndromes

The prognosis is good with early intervention, before the development of complications. 

The complications of subclavian artery thrombosis are the following:

1. Morbid upper arm ischemia (57%)
2. Upper limb claudication
3. Upper extremity pain at rest
4. Fingers embolization
5. Vertebrobasilar insufficiency from steal syndrome (37%)
6. Anginal symptoms from coronary steal via Intermammary artery graft (21%)
7. Leg claudication in the presence of axillofemoral graft

Procedural complications are as follows:

• Stroke
• Subclavian artery dissection
• Transient ischemic attack (TIA)
• Distal emboli
• Thrombosis
• Hematoma
• Bleeding
• Access site infection or bleeding

Smoking cessation is paramount in cases of atherosclerosis. The patient should receive counsel and education regarding the dangerous consequences of continued smoking which can literally threaten both life and limb due to the progression of atherosclerosis to other vasculature of the body. 

Subclavian artery thrombosis is a rare presentation, but when it occurs, it is often symptomatic. The condition is best managed by an interprofessional team that includes a cardiologist, radiologist, vascular surgeon, and an interventionalist. It is essential to treat the condition causing the subclavian artery thrombosis, and this will also include reducing risk factors like smoking, hypertension, hyperlipidemia, and diabetes.