Thyroid

Thyroid steal syndrome secondary to active hyperthyroidism

CT-angiogram-of-the-head,-axial-cut-(A)-and-sagittal-cut-(B)-demonstrating-atherosclerotic-changes-in-the-right-clinoid-ICA-(red-arrow)-resulting-in-approximately-70%-stenosis-per-WASID-criteria.-

Thyroid steal syndrome (TSS) is a rare condition characterized by a recurrent transient ischemic attack (TIA) that is found to be due to a large thyroid goiter or a dysregulation of thyroid hormones causing a diversion of blood flow from the cerebral circulation. Here we report the case of a patient with a history of multiple TIAs that were initially thought to be due to intracranial arterial stenosis based on CT angiography (CTA) findings, but later found to be secondary. to a hyperthyroid state causing TSS. To our knowledge, this is the very first reported case of TSS secondary to hyperthyroidism and only the second case of TSS secondary to thyroid hormone dysregulation.

introduction

Most transient ischemic attacks (TIAs) are the result of blockage or narrowing of intracranial blood vessels. However, diversion of blood from cerebral circulation due to pathology involving extracranial blood vessels can also lead to TIA. This is the case with the rare condition known as Steal Thyroid Syndrome (TSS). TSS is a condition characterized by episodes of transient cerebral ischemia that occur as a result of the “stealing” or diversion of blood from the brain to the thyroid due to thyroid goitre and, less commonly, thyroid hormone dysregulations . [1]. Patients with this condition usually have a history of multiple TIAs and present on angiography with enlarged thyroid arteries as part of a large goiter or thyroid hormone dysregulation. [1-3]. Only four cases of TSS have been clearly documented in the literature, three of which were secondary to thyroid goiter [1-3]. In this case report, we present a rare case of TSS secondary to an active hyperthyroid state, the likes of which have never before been documented in the literature.

Presentation of the case

A 45-year-old man with a medical history of insulin-dependent diabetes mellitus and peripheral arterial disease presented to the emergency department with complaints of two episodes of left hemiparesthesia and hemiplegia within the past three months. The patient reported that the first episode lasted 30-40 minutes and the second lasted two hours. On arrival at the emergency room, the patient was tachycardic with a heart rate of 129 and hypertensive with a blood pressure of 139/77. There were no focal neurological deficits on initial physical examination. Initial lab work revealed blood glucose 505, thyroid-stimulating hormone (TSH) <0.015 mIU/L (normal range: 0.465-4.68 mIU/L), free T4 4.52 ng/ dL (normal range: 0.78-2.19 ng/dL), anti-thyrotropin receptor antibody 4.64 IU/L (normal range: 0.00-1.75 IU/L) and thyroid microsomal antibody 299 IU/mL (normal range: 0-34 IU/mL). Initial non-contrast head computed tomography (CT) showed no acute intracranial abnormalities. Head CT angiography (CTA) reported no intracranial great vessel occlusion, but neck CTA reported greater than 70% stenosis of the right clinoid internal carotid artery (ICA) up to 50 % left petrous, cavernous and clinoid ICA stenosis and >50% stenosis of intradural right vertebral artery (Figure 1).

Follow-up brain MRI revealed no acute intracranial abnormalities. A bleb echocardiogram was performed and revealed an ejection fraction of 60% to 64% with no evidence of a patent foramen ovale. The patient’s TIAs were initially attributed to symptomatic right intracranial ICA stenosis. Digital subtraction cerebral angiography (DSA) showed mild atherosclerotic changes, but excluded significant flow limiting extra or intracranial stenosis (Figure 2).

However, the study revealed prominent bilateral thyrocervical trunks with prominent vascular blush of the thyroid gland (Figures 34). These findings, together with laboratory findings indicating hyperthyroidism, led to consideration of the diagnosis of TSS. The patient was initiated on methimazole and propranolol for the treatment of hyperthyroidism and was discharged with an endocrinology follow-up plan.

Discussion

TSS was first described in 1982 in a patient who presented with a TIA after treatment for hyperthyroidism that rendered the patient hypothyroid. The patient showed significant dilation of the arteries supplying the thyroid on cerebral angiography. After discontinuation of antithyroid medications, patient was rendered euthyroid and symptoms of TIA ceased [1]. In this case, it was theorized that the increase in thyroid blood flow was stimulated by the high levels of TSH (> 100 mIU/ml) [1,4]. The other three documented cases of TSS all involved patients who presented with recurrent TIAs and who presented with a large thyroid goiter [2,3]. In all three cases, the arteries supplying the thyroid were found to be enlarged by cerebral angiography, and surgical removal of the thyroid resulted in long-term prevention of symptom recurrence. [2,3]. In these cases, it has been hypothesized that the development of a large goiter leads to increased dilation of the thyroid arteries and increased blood flow to the goiter, leading to compromised carotid artery flow. [2,3].

To our knowledge, we report the first case of TSS that is the result of an active hyperthyroid state, and only the second case of TSS that is the result of thyroid hormone dysregulation rather than thyroid goiter. Unlike previously reported cases of TSS, in our case the increased blood flow and thyroid vascularity that led to the steal phenomenon did not occur due to elevated TSH or goiter. thyroid, as our patient had neither. The patient’s high anti-thyrotropin receptor antibody levels likely account for the increased thyroid vascularity and blood flow, as these antibodies are able to mimic the effect of TSH. [5].

Another element that distinguishes this case from previous cases of TSS is the use of head and neck CTA prior to cerebral DSA. Previous reported cases of TSS presented for initial evaluation from 1977 to 1986 [1-3]. As the first CTA was only made in 1992, the CTA was not an option at the time. [6]. In this case, head and neck CTA reported >70% atherosclerotic cavernous/supraclinoid segment stenosis of the right ICA, which was not supported by follow-up cerebral DSA (Figures 12). While CTA is widely regarded as an accurate and less invasive tool for estimating the degree of stenosis in carotid arteries, more recent studies comparing CTA and DSA have demonstrated poor estimation of carotid stenosis by CTA [7]. One such study demonstrated that of 90 patients with significant carotid stenosis on CTA, only 70 patients subsequently had significant carotid stenosis on DSA. [7]. While there was strong agreement between CTA and DSA when CTA estimated carotid stenosis >90%, agreement was much weaker when CTA estimated carotid stenosis 50%-70% [7].

TSS should be considered in the context of any patient with transient neurological symptoms who present with a large thyroid goiter on examination or laboratory evidence of thyroid hormone dysregulation. It is important to consider TSS as the possible etiology in patients with recurrent TIAs even after demonstration of carotid stenosis by CTA, as CTA may underestimate carotid stenosis, especially when the reported stenosis is of 50 to 70%. [7]. Correctly diagnosing TSS is crucial, as the condition is treated by addressing the underlying cause. This means surgery for thyroid goiter and medical care for thyroid disorders. [1-3].

conclusion

Here we present the first reported case of TSS secondary to a hyperthyroid state and only the second case of TSS due to dysregulation of thyroid hormones. The diagnosis of TSS should be considered in all patients with recurrent TIA and concurrent goiter and/or thyroid hormone disorder. This case highlights the importance of being aware of this entity, as there is potential for CTA findings to direct the clinician to other etiologies.