Deepak Gulati, MD
TIAs are associated with an increased risk of debilitating recurrent stroke along with increased risk for cardiovascular morbidity and mortality. Several studies have demonstrated poor agreement regarding TIA diagnosis among Emergency Department (ED) physicians, neurologists, and even stroke specialists. Although many biomarkers for TIA diagnosis are promising, none has been proven to be sufficiently reliable for diagnosis of TIA. Substantial international variation exists in clinical practice and policies for hospital admission for patients with TIA. International guidelines also differ in their recommendations for brain and vascular imaging after TIA, with imaging either immediately or several days after symptom onset, and brain imaging by either CT or MRI recommended. It has been reported that CTP shows focal perfusion deficits in up to a third of suspected patients with TIA and could also predict functional outcome at 3 months. It has been shown that limiting urgent assessment to patients with a score of 4 or more on ABCD2 would miss approximately 20% of those with early recurrent strokes. There appears to be a need for more research focus on dynamic imaging modalities like CTP or MRP, in addition to clinical information for better diagnosis and management of TIA.
This study by Meyer et al. aimed at determining independent factors associated with focal perfusion abnormality (FPA) in patients with supratentorial TIAs. The study included 265 patients with supratentorial TIA with CTP of good quality. Focal perfusion deficit was defined as hypoperfusion (prolonged MTT or reduced CBF) or hyperperfusion (reduced MTT or increase CBF). 42% of patients were found to have focal perfusion deficits (majority (97.3%) as hypoperfusion).
The significant positive associations of FPA were found with NIHSS on admission, right hemispheric symptoms, cardioembolic mechanism, symptoms persistence during CTP, intracranial arterial pathology and extracranial occlusion. A significant negative association was found with TIA duration. MRI Brain was performed within 15 days of symptom onset in about 41% of study patients and showed an acute or subacute ischemic lesion within TIA territory in 47.7%. A low sensitivity (59.6%) was found for the association between FPA and acute/subacute ischemic lesions, whereas several patients with FPA did not develop MRI lesions (specificity of 73.7%).
The NIHSS is shown to be proportional to the size of ischemic lesion, as expected, and is found to be related to FPA in this study. Right hemispheric symptoms usually yield to lower NIHSS as compared to left hemispheric symptoms for the same size of ischemic lesion. This could explain one of the reasons for association found between FPA and right hemispheric symptoms (likely high NIHSS/large right sided lesion included in this study). This study shows, contrary to the current evidence in literature, a negative association between FPA and TIA duration, which could be a sampling bias as per authors. The cardioembolic mechanism association with FPA could be explained by the tendency of cardiac emboli to cause larger cortical lesion, easily detected using CTP.
Limitations of the study include its retrospective, non-randomized and observational nature. Patients were included on the basis of ‘time-based’ definition of TIA, so the study population is not entirely reflective of TIA based on the current ‘tissue-based’ definition. CTP in this study provided incomplete hemispheric coverage, and FPA’s were not searched in brain regions incompatible with symptoms, which could have missed other potential FPA.
CTP must be weighed against several disadvantages of the technique in the setting of TIA, including increased radiation exposure, increased contrast administration, less sensitivity for small ischemic strokes along with significant variability in technique and processing of CTP between different institutions. There is also shown the low sensitivity of CTP in accurately diagnosing clinical strokes especially with low NIHSS/small strokes and TIA. CTP could still provide complementary information in TIA after weighing the risk involved. Accurate diagnosis and risk stratification of patients presenting with TIA are essential. The ABCD2 scoring system performs well in identifying TIA patients at high risk but does have some potential shortcomings, including no consideration to underlying mechanism and using only clinical information.
Considering the relative limited spatial resolution of CTP in combination with the often small size of infarcts, one of the potential areas of research is to evaluate the predictive role of Whole Brain-CTP in TIA in both supratentorial and infratentorial territories, especially in the presence of non-localizing symptoms. CTP may be of use to distinguish TIA’s from TIA mimics. CTP could provide additional information in addition to CT/CTA and MRI-DWI.
