We found that 11.1% of the TA patients in this study experienced stroke events, which is consistent with previous prospective studies.4
Stroke is an uncommon symptom for most TA patients and is rarely reported as the first manifestation; however, Sikaroodi et al.14
reported one case of stroke as the first manifestation of TA. In our study, 52.3% of stroke patients were first diagnosed with TA upon admission for an initial stroke event. It is recommended that if suspected, young stroke patients should be examined for TA based on nonspecific systemic symptoms such as fever, malaise, dizziness, and arm claudication.
The mean age of diagnosis for TA was in the third decade, and did not significantly differ between the stroke and nonstroke TA groups. The mean time from TA diagnosis to stroke onset was 1.6 years (range 0-4 years). Strokes developed in TA patients at much a younger age than observed for strokes related to atherosclerotic mechanisms. The prevalence of conventional stroke risk factors, except for hypertension and dyslipidemia, was lower among the TA patients than for traditional atherosclerotic stroke. The relatively high prevalence of hypertension is probably due to the involvement of renal artery stenosis.4,15
Therefore, stroke in TA patients seems to develop via a different mechanism than conventional atherosclerotic changes. The TA-related serologic markers erythrocyte sedimentation rate and C-reactive protein, which represent disease activity, also did not differ significantly between the stroke and nonstroke groups. However, the time intervals from stroke onset to laboratory studies were inconsistent and relatively long. Therefore, a homogeneous large study of acute stroke in TA patients is needed to establish a correlation between TA disease activity and ischemic stroke.
Known predispositions to stroke in TA patients were previously limited to TMB history. Also known as amaurosis fugax, TMBs are TIAs involving the anterior cerebral circulation and are caused by thromboembolisms or hypoperfusion. Previous studies have suggested that TMB history is a warning sign for stroke.16,17
Our data indicated that previous TMB may also be related to future ischemic stroke in TA patients.
MRI analysis revealed that most of the ischemic lesions were located at MCA branches or in the internal/cortical border-zone area. Large lobar type and cortical border-zone infarctions were documented in 33.3% and 28.6% of cases, respectively. Wedge-shaped large lobar and cortical border-zone infarctions are related to embolic mechanisms.18
In comparison, internal border-zone infarctions - which are known to occur via a hemodynamic compromise mechanism19
- accounted for only 4.8% of all the stroke events. These results highlight not only the hemodynamic compromise in large-artery stenosis but also the thromboembolic mechanism in ischemic stroke of TA. There were no cases of a small subcortical infarction suggesting a lacunar infarction among our TA patients.
As noted above, most TA patients are young and rarely have conventional atherosclerotic risk factors. With respect to atherosclerotic carotid stenosis, embolic cerebral infarction is usually attributed to plaque rupture or thrombotically active carotid plaques associated with high inflammatory infiltrates.20,21
Some studies have revealed premature atherosclerosis in TA patients based on ultrasonography or autopsy results.22-24
In particular, Seyahi et al.15
reported that 27% of TA patients possessed atherosclerotic plaques.23
From this, we can surmise that a similar mechanism may be involved in creating thromboembolisms, such as ruptures of atheromatous plaques or artery-to-artery embolisms.
Most previous reports have described TA as medium- or large-vessel arteritis involving the aorta and its main branches.1,4
To the best of our knowledge, only three case reports have described ICAS in TA, as discovered at autopsy or through arteriographic findings. Klos et al.26
described two patients with TA who had ischemic stroke due to intracranial involvement, in whom the cause of the infarction was proposed to be vasculitis.25
In our study revealed that more than half of the TA patients with stroke had ICAS. Based on our results, we believe that intracranial involvement in TA may be under-recognized, and that cerebral angiography should be considered for patients diagnosed with TA. Given that TA patients are young and relatively free from atherosclerotic risk factors except hypertension and dyslipidemia, vascular inflammation may be an important risk factor in ICAS.22
From our analysis of the stroke subgroup distribution, ICAS seems to be more likely when patients have large deep subcortical infarctions and internal border-zone infarctions than other types of infarction. A recent study regarding lesion patterns in cases of concurrent atherosclerosis of ICAS revealed a high prevalence of perforating artery infarctions and border-zone infarctions in the ischemic lesion distribution.27
Previous studies have suggested that ICAS is related not only to artery-to-artery embolisms but also to hemodynamic compromise.18,28-31
Further studies with large case series are needed to confirm whether ICAS in TA patients is related to a diverse pattern of ischemic stroke.
This study was subject to several limitations. First, since many of the patients were referred to our hospital some time after their stroke events occurred, laboratory and image data were not homogeneous. Some patients were diagnosed by FLAIR imaging because no DWI images were available. Although FLAIR imaging is less sensitive than DWI, we were still able to diagnose and locate stroke lesions accurately using clinical correlations. Second, only a small number of stroke patients were included in order to analyze stroke risk factors and ICAS between lesion subtypes. The low prevalence of stroke in TA made it impossible to include a large number of stroke patients in our analysis; however, this study currently represents the largest clinical series regarding stroke in TA patients. Third, the prevalence of ICAS in TA patients with stroke was higher than in previous studies. Some partial reanalyzed steno-occlusive arterial states produced by a proximal arterial embolic source were thought to have contributed to the high prevalence of ICAS. Moreover, the measurable degree of stenosis may vary between MRA and conventional angiograms. Although we analyzed the source images to reduce the possibility of overestimation of stenosis, MRA may overestimate the degree of ICAS. Directly comparing the ICAS prevalence between our study and previous studies is impossible due to different criteria being used for patient selection. We classified the lesion pattern as identified on DWI or FLAIR images; however, the chronic large-artery steno-occlusive state may alter the collateral flow and cerebral artery territory, which may limit the ability to establish the stroke mechanism in TA patients using lesion pattern analysis alone. Future investigations with perfusion images and conventional angiography would be helpful in determining the stroke mechanism. The final limitation of this study is the lack of pathologic proof of vasculitis. However, considering that the American College of Rheumatology Criteria for the Classification of TA yielded a sensitivity and specificity of more than 90%, there is little likelihood of overdiagnosis of TA in patients with conventional risk factors for stroke.10
The factor that was most associated with stroke in TA patients was previous TMB history. The finding that large lobar, cortical border-zone, and large deep infarctions were common stroke types suggests that a thromboembolic mechanism underlies stroke in TA. Furthermore, ICAS may be more prevalent in TA than was previously thought, which suggests that intracranial involvement is relatively common in TA. Future studies involving large numbers of subjects and focusing on the precise pathophysiological mechanisms leading to stenosis would help our understanding of its relationship with ischemic stroke in TA patients.