The neurological deficits of an ischemic stroke can manifest as sensory, motor, or a combination of both [1]. In most cases, motor weakness is more common and has a greater impact on the patient's mobility [2], [3]. However, sensory strokes can also prove devastating for the patients, as observed in the cases of Wernicke's aphasia and Dejerine-Roussy syndrome [4], [5]. Moreover, a lacunar stroke involving the internal capsule or the brainstem could be as devastating as a blockage in a larger blood vessel is [6]. As a result, the significance of the neurological deficit depends on the size and location of the ischemic core. The effects can range from limited sensory or motor weakness to more generalized symptoms, including neglect, mixed sensory-motor weakness, visual field loss, ataxia, aphasia, and impaired consciousness. If the ischemic core is large or involves the posterior circulation, it can affect the patient’s consciousness [7], [8].

The National Institute of Health Stroke Scale (NIHSS) is a standard 15-item neurological scale for the assessment of stroke severity [9]. Each clinical item is graded on a scale of 3–5 points; zero represents a normal function. If the patient has sensory aphasia or is unconscious, the untestable items may be excluded from the scoring. The cumulative scores range from 0 to 42, with higher scores indicating a more severe stroke, often associated with a large vessel occlusion [10]. Typically, small vessel occlusions yield lower scores, except when critical areas like the internal capsule or brainstem are affected, resulting in higher NIHSS score, falsely suggesting a large vessel occlusion [11]. Moreover, a slow in-situ occlusion of a large vessel, infarction of the sensory predominant occipital lobe, a large segment's dissection of a vessel with reduced flow to its distal territory, and a large vessel occlusion with good collaterals may have lower scores at presentation and can falsely suggest a small vessel occlusion [12].

While predicting large vessel occlusions, the 6-point cutoff exhibits a sensitivity rate of 97 % and a limited specificity value of 27 % [13]. At this rate, there is a high likelihood of false-positive predictions rendering it less effective as compared to other scales [15], [14]. It produces false-positive results in 73 % of cases, indicating an overly sensitive response to large vessel occlusions. Three-fourths of ischemic stroke patients can get false-positive indications for mechanical thrombectomy. Perhaps higher NIHSS thresholds could more effectively predict these true-negative cases, considering the difficulty for small infarcts to attain higher scores.

To evaluate the sensitivity and specificity, the scale’s predictions are compared to the outcome of brain angiography. However, angiography only provides information on two types of vessel occlusions; a large vessel and a medium vessel. We cannot develop vessel-caliber categories with angiography for analyzing and comparing the predictive accuracy of the 6-point scale and higher NIHSS thresholds using area under the receiver operating characteristic curves (AUROC) [16]. It is particularly challenging to determine the exact size of an ischemic infarction using angiography, especially for the numerous distant and deep penetrating branches of the brain. In light of this, we propose the formation of different infarct-size categories using plain computed tomography (CT) imaging. Subsequently, these categories were predicted sequentially using both higher NIHSS thresholds and the conventional 6-point scale. The approach enabled a thorough assessment and comparison between higher NIHSS thresholds and the conventional 6-point scale.