What Is a Minor Stroke?
Background and Purpose— The term “minor stroke” is often used; however a consensus definition is lacking. We explored the relationship of 6 “minor stroke” definitions and outcome and tested their validity in subgroups of patients.
Methods— A total of 760 consecutive patients with acute ischemic strokes were classified according to the following definitions: A, score ≤1 on every National Institutes of Health Stroke Scale (NIHSS) item and normal consciousness; B, lacunar-like syndrome; C, motor deficits with or without sensory deficits; D, NIHSS ≤9 excluding those with aphasia, neglect, or decreased consciousness; E, NIHSS ≤9; and F, NIHSS ≤3. Short-term outcome was considered favorable when patients were discharged home, and favorable medium-term outcome was defined as a modified Rankin Scale score of ≤2 at 3 months. The following subgroup analyses were performed by definition: sex, age, anterior versus posterior and right versus left hemispheric stroke, and early (0 to 6 hours) versus late admission (6 to 24 hours) to the hospital.
Results— Short-term and medium-term outcomes were most favorable in patients with definition A (74% and 90%, respectively) and F (71% and 90%, respectively). Patients with definition C and anterior circulation strokes were more likely to be discharged home than patients with posterior circulation strokes (P=0.021). The medium-term outcome of older patients with definition E was less favorable compared with the outcome of younger ones (P=0.001), whereas patients with definition A, D, and F did not show different outcomes in any subgroup.
Conclusions— Patients fulfilling definition A and F had best short-term and medium-term outcomes. They would be best suited to the definition of “minor stroke.”
The term “minor stroke” is often used for stroke patients with mild and nondisabling symptoms. However, a consensus definition is lacking. We performed a structured literature search of MEDLINE from 1950 to May 2009 with the key word “minor stroke(s)” and found 670 articles with the term in the abstract (568 articles) or the title (102 articles). Most authors did not define their meaning of “minor stroke.” In the journal, Stroke, the most relevant specialist journal on cerebrovascular diseases, only 25 of 75 articles provided a definition. All authors giving a definition tried to capture stroke syndromes with mild and nondisabling symptoms, but their definitions varied considerably (see supplemental Appendix, available online at http://stroke.ahajournals.org).
Patients are selected for trials and epidemiological studies based on the syndrome of a “minor stroke.”1,2 Therefore, a broadly acceptable concept and definition of “minor stroke” is required. Ideally, a definition of a “minor stroke” should reflect the following aspects: (1) it should capture patients with mild and nondisabling symptoms in acute stage and favorable short-term and medium-term outcomes; (2) it should be valid for different subgroups of stroke patients; (3) it should imply both qualitative and quantitative dimensions; (4) it should be simple and useful in daily clinical practice; and (5) it should not overlap with the definition of a transient ischemic attack (TIA).
The National Institute of Neurological Disorders and Stroke (NINDS) rt-PA Stroke Study Investigators developed 5 working definitions of “minor stroke” based on information limited to the CT scan and clinical presentation, specifically, the baseline NIHSS score, baseline NIHSS individual items, and baseline stroke subtype.3 However, these 5 definitions have not been tested in clinical practice, and none have been adopted in stroke research.
We tested these definitions of “minor stroke” and the definition most often used according to our literature search (NIHSS ≤3) in the Bernese Stroke cohort. We explored the relationship of the 6 definitions with short-term and medium-term outcomes and tested the validity in different subgroups of stroke patients.
Patients and Methods
The University Hospital of Bern (Inselspital) is a large teaching hospital providing tertiary care for >1 million people and primary care for the urban area of Bern, with 300 000 inhabitants. This indicates that we receive and admit both severe strokes from distant areas and mild and severe strokes and TIA patients from the city area. Most patients with a TIA or stroke are usually admitted for treatment and further investigation. From January 2000 to December 2005, 815 patients with acute ischemic strokes (time from symptom onset to presentation ≤24 hours) were admitted to the ward of the Department of Neurology. Patients with retinal artery occlusions and TIAs, defined as a focal cerebral ischemic event with symptoms lasting <24 hours, were excluded. Some aspects of these patients have been reported previously.4,5
All patients were examined immediately after admission by a neurologist, and the deficit was scored using the NIHSS.6 Demographic data and time of symptom onset were recorded. After clinical evaluation, patients underwent a standard investigation protocol in the emergency department, including blood tests, ECG, cranial CT, or MRI. Status of extracranial and intracranial vessels was assessed by neurovascular ultrasound, CT angiography, magnetic resonance angiography, or digital subtraction angiography. Based on the ischemic lesions on the CT or MRI scan, infarctions were classified into anterior and posterior circulation and right and left hemispheric strokes. The following stroke risk factors were assessed: sex, hypertension, diabetes, current cigarette smoking, hypercholesterolemia, coronary heart disease, previous TIA or stroke, and a family history of TIA and stroke. Stroke etiology was classified using the Trial of Org 10172 in Acute Stroke Treatment criteria after a complete diagnostic work-up.7
Seventeen patients (2%) underwent intravenous therapy (<3 hours of onset), 146 (32%) intra-arterial thrombolysis (<6 hours of onset), and 21 (3%) mechanical thromboaspiration, according to international guidelines and our institutional protocol.8,9 Antithrombotic and secondary preventive therapy was given according to European guidelines.10,11 All patients were admitted to the neurological ward. Patients with disabling stroke symptoms including neuropsychological deficits such as aphasia, visuospatial deficits, or neglect were then transferred to the rehabilitation unit; those with nondisabling strokes were discharged home.
Definitions of “Minor Stroke”
Based on clinical presentation, baseline NIHSS score, and baseline NIHSS items, we classified all patients for this study into “yes” or “no” for each definition A through F. The definitions are summarized below. Thirty-eight patients (4.7%) could not be classified because clinical records were inadequate to classify them into all of the 6 definitions.
The 6 definitions of minor stroke used in this study:
A. all patients with a score 0 or 1 on every baseline NIHSS score item, except level of consciousness items (items 1a to 1c), which must be 0;
B. all patients with a lacunar-like syndrome (presumed small-vessel occlusive disease) such as pure sensory syndrome, pure motor hemiparesis, sensorimotor syndrome, ataxic hemiparesis, and dysarthria-clumsy hand syndrome;
C. all patients with only motor deficits (can include dysarthria or ataxia) with or without sensory deficits. These patients can have only a combination of motor, coordination, and sensory deficits without any deficits in the spheres of language, level of consciousness, extinction or neglect, horizontal eye movements, or visual fields, deficits generally ascribed to larger territories of focal ischemia;
D. all patients with baseline NIHSS in the lowest (least severe) quartile of severity (NIHSS ≤9), excluding all patients with aphasia, extinction, or neglect, or any points on the level-of-consciousness questions;
E. all patients with baseline NIHSS in the lowest (least severe) quartile of severity (NIHSS ≤9); and
F. all patients with baseline NIHSS ≤3.
Short-term outcome was considered favorable when patients were discharged home from our hospital and unfavorable when they died or were referred to a rehabilitation unit or another hospital. Medium-term outcome was assessed 3 months after stroke using the modified Rankin scale.12 A total of 41.4% of patients were examined clinically, and 58.6% were interviewed by phone. A good outcome was defined as a modified Rankin Scale score of 0 to 2. Telephone interviews were performed by physicians and study nurses experienced in the use of the modified Rankin Scale. Recurrent vascular events after hospital discharge such as TIA, recurrent stroke, or myocardial infarction were recorded. Seventeen (2.1%) of 815 patients were lost for follow-up.
Quantitative data are expressed as mean values±1SD. The NIHSS score on admission is given as median value. Data are reported in frequency tables. Effect of different variables on clinical outcome among patients with each of the 6 definitions was assessed using Fisher exact test for comparison of proportions. The following variables were assessed: sex, age (>65 years versus ≤65 years), anterior versus posterior circulation strokes, right versus left hemispheric stroke (those with bilateral, cerebellar, or brain stem ischemia were excluded for this subanalysis), and early (0 to 6 hours) versus late presentation (6 to 24 hours). P<0.05 was considered significant.
Baseline characteristics, clinical information and stroke etiology of all 760 patients included in this analysis are presented in Table 1. Table 2 summarizes the number of patients fulfilling “minor stroke” definitions A through F and their characteristics. Median NIHSS on admission was lowest in patients with definitions A and F and highest in those with definition E. Short-term and medium-term outcome was best in patients with definitions A and F and worst in those with definitions C and E (Figure 1). The number of recurrent vascular events at 3 months among patients with different definitions was comparable and low (range, 0.6 to 2.5%). Outcome in nonthrombolyzed patients compared with all patients in the corresponding definition group was similar (Table 3). Supplemental Table I (available online at http://stroke.ahajournals.org) shows subgroup analyses of short-term and medium-term outcomes. Patients with definitions B and E presenting after 6 hours were more likely to be discharged home than patients presenting within the first 6 hours (P=0.048 and P=0.019, respectively). Patients with definition C experiencing an anterior circulation stroke were more likely to be discharged home (P=0.021) than those with posterior circulation strokes, and older patients with definition E were more likely to be handicapped at 3 months than younger patients (P=0.001). Patients with definition A, D, and F did not show different outcomes in any subgroup. However, older patients with definition A tended to be handicapped after 3 months more frequently than younger patients (P=0.054). Figure 2 shows short-term and medium-term outcomes in relation to stroke severity, measured with the NIHSS score at admission.
In this study, we assessed the outcome of 760 stroke patients classified as “minor stroke” according to 6 different definitions. Definition A (score 0 or 1 on every baseline NIHSS score item and normal level of consciousness) and definition F (NIHSS ≤3) would be best suitable to the concept of “minor stroke”: patients with definition A or F were most likely to be discharged home and to be independent at 3 months.
Definition F was valid for all subgroups of stroke patients. In addition, definition F is easily applicable in clinical practice and relies on NIHSS total score. Several eminent groups in stroke research have adopted this definition.13,14 However, using a specific cut point of the NIHSS for defining a minor stroke might provoke criticism and raise the question why a stroke with an NIHSS score of 3 should be minor but with an NIHSS score of 4 not? Figure 2 relates NIHSS scores and short-term and medium-term outcome: two thirds of patients with an NIHSS score of ≤3 were discharged home. The difference for patients with an NIHSS score of 4 is not impressive, whereas a significant number of patients with NIHSS scores of ≥5 have a less favorable short-term outcome compared with patients with scores of ≤4. This illustrates how arbitrary a cut point is. There is no real scientific reason to choose a cut point of 3 or 4. Therefore, it would be desirable to define a cut point for “minor stroke” by consensus of several stroke researchers.
A minor stroke patient, according to definition F, could have a severe deficit in one NIHSS item or a mild deficit in more than one item. Some stroke physicians would consider the first situation (eg, hemianopia=2 points) more severe than a mild facial weakness combined with dysarthria (ie, 1 plus 1=2 points). Definition A circumvents this problem. According to this definition, “minor stroke” includes only patients who are conscious and score ≤1 on each NIHSS item. This means that definition A includes only patients who show mild but no severe functional deficits in any NIHSS item. The limitation of this definition according to our results is that it might not be entirely robust for all subtypes of stroke patients.
Patients classified with definition D had worse short-term outcomes than patients with definitions A and F. Nevertheless, definition D merits some discussion; it includes all patients with an NIHSS score of ≤9 but excludes patients with decreased consciousness or neuropsychological deficits such as aphasia, extinction phenomena, or neglect. Medium-term outcome of patients with minor stroke definition D was favorable in quasi as many patients as with definition A or F, although the cutoff of the NIHSS score was considerably high. Furthermore, this definition turned out to be robust in many subgroups of stroke patients.
Less than 60% of patients with definitions B, C, and E were independent enough to be discharged home. Furthermore, these definitions were not robust for all subgroups of stroke patients. In addition, more patients with definitions B, C, and E compared with definitions A, D, and F had significant disabilities at 3 months. Therefore, these definitions are less suitable to define a “minor stroke.”
Thrombolysis might have influenced short-term and medium-term outcomes in patients with different definitions of a minor stroke. Therefore, patients without thrombolysis were analyzed separately (Table 2). Outcome in nonthrombolyzed patients compared with all patients in the corresponding definition group was similar. However, only a minority of patients with different definitions of “minor stroke” underwent thrombolysis, ranging from 2% to 15%. Whether thrombolysis is beneficial in patients with different definitions of a “minor stroke” cannot be derived from this study. However, in a previous analysis, we assessed outcome in patients with mild and rapidly improving symptoms; overall, 75% of these patients had a favorable outcome (modified Rankin Scale score 0 to 1).4 Baseline NIHSS score ≥10 points increased the odds of unfavorable outcome or death 17-fold, and proximal vessel occlusion increased the odds 7-fold. Therefore, selected patients, especially those with proximal vessel occlusions and baseline NIHSS scores ≥10 points, are likely to derive a benefit from thrombolysis. In a post hoc subgroup analysis of the NINDS study, no difference in the beneficial effects of tissue plasminogen activator in patients with minor stroke syndromes compared with the overall treatment effects in the entire cohort could be detected.3 Our current policy is to work up all TIA and minor stroke patients rapidly and base our treatment decisions (IV thrombolysis, endovascular treatment, or no treatment) on the clinical evolution and the results of the ancillary investigations.
The present definitions of a “minor stroke” are based on clinical deficits and exclude information obtained from imaging. CT scans of patients with mild deficits are often normal in the acute stage of a stroke. However, nearly all patients with neurological signs lasting >24 hours show abnormalities on diffusion-weighted imaging. A combination of clinical signs and information from diffusion-weighted imaging might define a “minor stroke” more accurately than a definition based on clinical information only. However, such a study has yet to be performed.
An important issue is the validity and interrater reproducibility of our minor stroke definitions. However, we cannot address this issue with the data of this study. All patients were categorized based on clinical presentation, baseline NIHSS score, and baseline NIHSS items by the first author. On the other hand, both the NIHSS, which relies on 4 of the 6 minor stroke definitions, and the modified Rankin Scale, on which we assessed outcome, have been used extensively in many trials.15–18 Their reproducibility and validity have been analyzed in many studies and are considered as being fair.
In conclusion, to date, there is no consensus on the definition of a “minor stroke.” Our study indicates that patients fulfilling definition A (conscious patients scoring ≤1 on every NIHSS item) and definition F (patients with NIHSS ≤3) had the best short-term and medium-term outcomes. They would be suitable best to define “minor stroke” for clinical and research purposes. Future consensus panels from international stroke organizations should consider a uniform definition of minor stroke to enhance clinical research.
The following are definitions of “minor stroke” used in the journal, Stroke:
small strokes with slight symptoms persisting for >24 hours (1976;7:444–451);
infarct with a minimal neurological residuum (1988;19:108–111);
symptoms persisting >24 hours, with complete or virtually complete recovery within 3 weeks (1989;20:59–64);
focal ischemic cerebrovascular event lasting >24 hours and resulting in minimal permanent neurological deficit, with ≥80% recovery of function within 3 weeks (1992;23:1723–1727);
predominantly sensory deficit limited to the upper limb of the dominant side, with the only functional limitation being that of slowing of fine-motor tasks (1997;28:2395–2399);
complete or nearly complete recovery (1999;30:2574–2579);
nondisabling stroke: patients were sufficiently well to remain at home after their event and to attend an outpatient clinic (2004;35:2459–2465);
no lasting neurological deficit (1995;26:57–62);
patients with a Scandinavian Stroke Scale of ≥44 points and able to return home after a week (1989;20:340–344);
Modified Rankin Scale ≤3 (1991;22:754–759; 1993;24:527–531; 1994;25:1611–1616);
Modified Rankin Scale ≤2 (1992;23:199–204);
Modified Rankin Scale=2 (1998;29:126–132);
Modified Rankin Scale 2 to 3 (2001;32:1425–1429);
new neurological deficit that persists >7 days and results in grades 1 or 2 on a modified Rankin Scale (2004;35:2134–2139);
new persisting neurological deficit that increased the National Institute of Health Stroke Scale (NIHSS) score by <3 points (2003;34:813–819; 2005;36:787–791);
new neurological deficit that either resolved completely within 7 days or increased the NIHSS score ≤3 (1996;27:2075–2079; 2001;32:2328–2332; 2002;33:725–727);
new neurological deficit that either resolved completely within 30 days or increased the NIH Stroke Scale (NIHSS) score ≤3 (2003;34:1936–1941; 2004;35:2862–2866); and
persistent focal neurological deficit with a baseline NIHSS ≤3 (2008;39:1717–1721; 2008;39:2461–2466).
We thank Neal Thurley for the support with the systematic literature search and Pietro Ballinari for statistical advice.
Sources of Funding
Urs Fischer was supported by the KK Foundation for Cardiology and Circulation and the Gottfried und Julia Bangerter Foundation.
- Received November 12, 2009.
- Revision received December 15, 2009.
- Accepted December 30, 2009.
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