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Threshold for NIH stroke scale in predicting vessel occlusion and functional outcome after stroke thrombolysis can change

Dear editor, Corany et al. showed that baseline National Institutes of Health Stroke Scale (NIHSS) scores of 12 and 11 were identified as markers of three-month modified Rankin Scale (mRS) score 2 and baseline vessel occlusion, respectively, in stroke patients treated with intravenous (IV) thrombolysis. This patient cohort is larger than all previous studies, but this study has several limitations. First, data on three-month mRS were available in 77.5% of patients. It is likely that most of the patients without follow-up were severely disabled or were dead, but it is uncertain whether they had higher baseline NIHSS. Approximately 10–15% of patients worsens during the first hours after IV thrombolysis and early neurological deterioration (END) is consistently associated with poor functional outcome at three months, but a higher NIHSS score at baseline is not a strong predictor of END. One-third of patients with minor stroke had three-month poor outcome after early progression of symptoms due to large vessel occlusion or early recurrence after rapid improvement due to small vessel reocclusion. In addition, NIHSS is not a disability score and individual items could produce quite different magnitudes of disability. Particular NIHSS items, such leg weakness of extinction/inattention, have been found to be independent risk factors for unfavorable outcome in minor stroke. One possible reason is that the mRS is highly focused on walking ability. Also, NIHSS has a potential weakness with respect to uneven scoring of lesion-specific neurologic deficits. For example, a right hemispheric stroke receives a low NIHSS score compared with the samesized left hemispheric stroke, partly because the NIHSS awards seven points for tests directly related to language function and only two points for neglect. NIHSS may not appropriately evaluate the spectrum of posterior circulation (PC)-related signs. The scale is highly weighted toward anterior circulation deficits, including cortical signs and motor function, while PC deficits, including cranial nerve signs and ataxia, receive fewer points; ataxia is frequently excluded from scoring due to the coexistence of motor deficits. Second, the authors did not report data on prestroke mRS. According to previous international stroke registries, at least slight preexisting disability is reported in 10% of cases treated with IV thrombolysis, and pre-stroke mRS 1, 2, and 3 is associated with increased risk of death at three months and lower chance of achieving favorable outcome. Preexisting disability may be due to previous stroke with neurologic deficits quantified by NIHSS but also to other conditions such as dementia or orthopedic disorders that that do not change baseline NIHSS score. Third, data on baseline vessel occlusion were available only in 20.3% of patients. It is likely that most of the patients without baseline computed tomography (CT)/magnetic resonance (MR) angiography had a lower baseline NIHSS. Fifty-four percent of the patients with minor stroke had visible arterial occlusion before IV thrombolysis. Also, lesion site as well as presence of single or combined occlusions highly reflects the observed NIHSS values. All these limitations may change the threshold for baseline NIHSS score in predicting functional independency using mRS score and baseline vessel occlusion.