Case Presentation: A 47 year old female with hyperlipidemia and diabetes presented to the ED for syncope, right sided weakness, and aphasia. She was evaluated with CT and CTA head/neck, which was negative for acute stroke but revealed critical left subclavian stenosis and an anomalous origin of the left vertebral artery (LVA) arising from the aortic arch directly. Vascular surgery, neurology, and radiology reviewed the imaging and concluded that given the variant anatomy, subclavian steal syndrome (SSS) would be unlikely. EKG and troponin were normal. She had returned to her neurologic baseline and was admitted for observation and further evaluation of syncope. She was hypotensive on arrival without reflex tachycardia or orthostasis. There was no evidence of infection, sepsis, or shock and no lab evidence of end organ dysfunction or electrolyte disturbance. Echocardiography was normal. Given a history of hypothyroidism, she underwent an endocrinologic evaluation. TSH, T3, T4, cortisol, ACTH level and stim test, FSH/LH, prolactin, growth hormone levels were all normal. Further discussion with the patient revealed a chronic history of episodic vertigo, ataxia, visual disturbances, and peripheral paresthesias as well as left arm weakness and fatiguability with overhead use. She denied prior episodes of syncope. Given these symptoms were fairly consistent with vertebrobasilar insufficiency and intermittent left arm claudication, SSS was reconsidered. Neurosurgery was consulted to perform cerebral angiography to definitively confirm or refute the presence of SSS despite the LVA arising proximal to the subclavian stenosis in the left arm. Angiography revealed retrograde flow in the LVA via the thyrocervical trunk reconstituting flow distal to the subclavian stenosis confirming the presence of SSS. The patient underwent subclavian stenting with improvement in her symptoms.
Discussion: Subclavian artery stenosis is asymptomatic in the majority of patients. SSS occurs when subclavian artery stenosis causes reversal of flow in the ipsilateral vertebral artery, diverting blood from the posterior circulation of the brain into the arm. SSS is relatively common with a reported prevalence anywhere from ~1-6%. Patients can present with arm pain, fatigue, paresthesia, particularly with exertion due to relative limb ischemia, or with neurologic symptoms of vertigo, visual changes, syncope, ataxia, tinnitus, or hearing loss reflective of the ‘steal’ physiology and relative vertebrobasilar insufficiency. Our patient had nearly all of these. Though well understood, reliance on anatomy alone to gauge suspicion may prematurely exclude disease and delay treatment. Anomalous vertebral artery origins are not uncommon, with aortic LVA occurring in 3-8% of people. Prior reports note similar cases where variant anatomy does not ‘protect’ against steal physiology despite blood flow being directly supplied by the aorta.
Conclusions: SSS should not be excluded solely based on anatomy. When symptoms are compelling, the only reliable way to confirm or refute the presence of SSS is with cerebral angiography to evaluate for the presence of retrograde flow ‘stealing’ blood from the brain’s circulation. As front line diagnosticians in the hospital, our case also reinforces the importance of being vigilant and mindful of cognitive bias, such as anchoring and premature closure, which led us briefly away from the primary diagnosis in pursuit of other explanations.