A Great Heist: Subclavian Steal Syndrome Causing Posterior Transient Ischemic Attack and Stroke

Abstract

Introduction

Subclavian steal syndrome is a phenomenon of arterial flow reversal secondary to occlusive disease in proximal subclavian arteries, occasionally resulting in neurologic sequelae.

Case Presentation

The authors present the case of a 67-year-old man with stroke risk factors and a history of receiving head and neck radiation therapy who developed subclavian steal physiology leading to a transient ischemic attack and posterior circulation stroke. He was medically optimized without substantial progression or recurrence of disease.

Conclusion

This case illustrates a case of vertebrobasilar transient ischemic attack and posterior circulation stroke from subclavian steal syndrome in the setting of prior radiation therapy manifesting as extremity weakness and discoordination. Further research on therapeutic radiation dosages and subsequent incidence of arterial disease which could contribute to subclavian steal syndrome is necessary.

Introduction

The phenomenon known as subclavian steal syndrome is underrecognized among emergency physicians as an etiology of stroke and transient ischemic attack. Subclavian steal describes a pathologic process in which blood flow is reversed through vertebral arteries secondary to a proximal stenosis or occlusion of the ipsilateral subclavian artery and siphoned to provide distal subclavian artery perfusion. ¹ Progressive stenosis eventually results in a pressure gradient large enough to favor retrograde flow through the circle of Willis and basilar artery system, producing a syndrome of cerebral and/or extremity malperfusion. ¹ The clinical presentation of this blood flow redirection can range from a lack of symptoms to extremity claudication or even effort-related syncope or stroke. ^1,2

Upon physical examination, subclavian steal can be suggested vascularly by discordant upper-extremity blood pressures (< 15 mmHg), supraclavicular or suboccipital bruits, or atrophic nails secondary to upper-extremity arterial insufficiency. ¹ The most common symptoms reported in subclavian steal syndrome include exercise-induced arm pain, fatigue, coolness, and paresthesia. More rarely, upper-extremity exercise can precipitate a vertebrobasilar insufficiency syndrome presenting as “drop attacks” or paroxysmal vertigo, diplopia, nystagmus, tinnitus, or hearing loss. ¹ Confirmatory imaging modalities include Doppler ultrasonography, computed tomography (CT) angiography, and magnetic resonance angiography. ^1,3

Treatment of subclavian steal depends on the severity of symptoms. In mild cases, the combination of medical therapy and observation has been utilized, as spontaneous improvement has been reported. In more severe cases, treatment is controversial, with most practitioners generally favoring percutaneous treatment. ^1,4 Percutaneous options for treatment include balloon angioplasty and stenting of diseased vasculature. Surgical treatment is reserved for longer or more distal subclavian occlusion and is fundamentally a vascular bypass procedure, most commonly carotid–subclavian bypass grafting. ^1,5

The authors present a case of subclavian steal syndrome manifesting in association with extremity movement in the setting of prior distant radiation therapy. Although many cases may not be clear through such a history, this case highlights the importance of eliciting aggravating or associated symptomatology with any neurologic complaint and reviewing any history of therapeutic radiation to anatomically adjacent structures. Prompt identification of this pathophysiologic state is important from the standpointintervention and cerebrovascular risk reduction.

Case Report

A 67-year-old man with a history of hyperlipidemia, tobacco use, and tonsillar carcinoma after resection and radiation therapy presented to the emergency department following an episode of discoordination and extremity “weakness” (greater on the left side than the right) that started suddenly when he stood up from a sitting position. This episode lasted 15 minutes, after which time he reported a return to baseline. Upon a review of systems, the patient also reported years of positional left-arm paresthesia, transient brief episodes of blurry vision in the left eye, and months of brief intermittent vertigo. Twelve years prior to presentation, the patient had received radiation therapy to his left neck cervical lymph nodes in the dose of 30 fractions of 200 cGy (totaling 6000 cGy), from which he had reported chronic dysphagia in prior practitioner visit notes. Initial vital signs were normal, with a blood pressure of 101/72. No contralateral blood pressure was recorded. The patient’s initial emergency-department history and physical neurologic examination were unremarkable; however, documentation through practitioner handoff made note of left-upper-extremity dysmetria, which had resolved upon subsequent examination by multiple practitioners. The National Institutes of Health Stroke Scale documented upon initial evaluation was scored 0. A complete blood count, chemistry panel, and urinalysis were obtained and were within normal limits. An electrocardiogram showed a normal sinus rhythm. A noncontrast CT scan of the head showed a remote left occipital infarct with no acute process. The patient was given aspirin, and the case was discussed with the on-call neurologist. A CT angiography study of the head and neck was performed (see Figure 1). It was negative for acute intracranial pathology but revealed a complete occlusion of the proximal left subclavian artery with reconstitution through the left vertebral artery, which was concerning for subclavian steal syndrome. A vascular surgeon was consulted and recommended Doppler ultrasound evaluation, which confirmed retrograde flow in the left vertebral artery consistent with subclavian steal syndrome. A subsequent magnetic resonance imaging brain scan revealed a late subacute infarct in the left occipital lobe consistent with findings on the noncontrast head CT scan.

Figure 1:

Coronal slice of head and neck computed tomography (CT) angiography scan demonstrating complete occlusion of the proximal left subclavian artery (red arrow/square) with reconstitution through the partially visualized left vertebral artery (green arrow/star).

Discussion

Subclavian steal syndrome is a phenomenon of distal arterial flow reversal secondary to occlusive disease in one or both proximal subclavian arteries. ¹ Distal arteries commonly affected include vertebral arteries and even coronary arteries in patients who have received a coronary artery bypass graft of the inferior mammary artery. ^1,6 The most common overall risk factor is atherosclerosis; however, vasculitis, external compression such as thoracic outlet syndrome, congenital abnormalities, radiation treatment, and stenosis from prior surgery or procedures have all been implicated. ^1,6 Although most cases of subclavian steal physiology are asymptomatic, the presence of subclavian steal is associated with increased morbidity and mortality related to disease burden in other vascular beds. ^1,3,6 If symptoms are present, arm claudication is the most common complaint. ¹ As in this case, patients have reported lateralizing symptoms of vertebrobasilar insufficiency, including syncope, dizziness, diplopia, nystagmus, tinnitus, and hearing loss. ^1,7 Dialysis fistulas due to the intrinsic high-flow state have also been shown to provoke or worsen subclavian steal physiology. ¹ In the case reported herein, the patient likely had both vertebrobasilar insufficiency and extremity malperfusion components to explain his symptomatology.

Treatment involves aggressive cardiovascular medical optimization including aspirin or statin blood pressure control. In severe or symptomatic cases, treatment options include percutaneous angioplasty, stenting, and surgical bypass, all of which have high success rates. ^1,3,8 Although, in general, percutaneous angioplasty with possible stenting is preferred because of the minimally invasive nature of the procedure, the selection of a particular treatment modality is often limited by the underlying anatomy. A completely occluded fibrotic or calcific vessel following radiation therapy may not be amenable to percutaneous recanalization, and treatment with carotid–subclavian bypass would be preferable. ⁹ In most cases, after recanalization, patients experience complete relief of extremity and neurologic symptoms in the absence of infarcted brain tissue. ^1,9,10 Restenosis of angioplasty repair is seen most often in completely occluded vessels and is estimated to occur in 7% to 41% at 5 years. ¹⁰ Failure of carotid–subclavian bypass is estimated to occur in 0% to 4% of cases at 5 years. ⁴ Well-known complications of carotid–subclavian bypass for subclavian artery occlusion include graft failure, postoperative bleeding, pseudoaneurysm, lymph fistula, chylothorax, Horner syndrome, recurrent laryngeal nerve palsy, phrenic nerve palsy, and stroke. ⁴ The increased apparent failure rate of endovascular repair of a subclavian steal lesion must be weighed against the risk of complications that come with the carotid–subclavian graft.

Radiation therapy is a widely used modality employed in modern cancer treatment. To date, there is no established dose–effect curve linking therapeutic radiation dose to the development of large artery disease, although numerous reports describe the development of subclavian and carotid stenosis in this setting. ^9,11–13 The pathophysiologic mechanism has been postulated to be related to accelerated atherosclerosis and/or induced fibrosis. ^12,14 Even the relatively lower doses of radiation used in Hodgkin lymphoma are associated with adverse effects, most notably accelerated coronary artery disease, cardiac valvular dysfunction, and carotid or subclavian artery disease. ^11–13 The median time from therapy to subclavian or carotid artery stenosis in these cases has been found to be approximately 21 years. The median low-cervical radiation dose for patients who developed subclavian stenosis was 4400 cGy. ¹² As the patient in this case was treated with a substantially higher total dose of radiation for his specific type of cancer (carcinoma, 6000 cGy), one could reason that this could explain his relatively accelerated course.

Conclusion

This case illustrates an instance of vertebrobasilar transient ischemic attack and posterior circulation stroke from subclavian steal syndrome manifesting as extremity weakness and discoordination. It is likely that the patient’s history of neck radiation contributed substantially to his subclavian artery occlusion. In addition, his prolonged symptomatology and subacute presentation can be explained by his subclavian steal syndrome and associated flow reversal physiology.

The patient was discharged with close follow-up including a Holter monitor and an echocardiogram, which were unremarkable. His symptoms remained stable for 3 months, at which point a repeat brain magnetic resonance magnetic resonance imaging scan was obtained and found to show no new infarction. The patient was seen in the vascular surgery clinic and was recommended to obtain ongoing medical management because of his clinical stability and subsequent spontaneous resolution of symptoms.