Published online before print August 4, 2005, doi: 10.1161/01.STR.0000177869.02361.dc
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(Stroke. 2005;36:1988.)
© 2005 American Heart Association, Inc.
Original Contributions |
Supratentorial Age-Related White Matter Changes Predict Outcome in Cerebellar Stroke
From the Department of Neurology, Universitätsklinikum Mannheim, University of Heidelberg, Mannheim, Germany.
Correspondence to Dr Michael Hennerici, Department of Neurology, Universitätsklinikum Mannheim, University of Heidelberg, Theodor-Kutzer-Ufer 1-3, 68135 Mannheim, Germany. E-mail hennerici{at}neuro.ma.uni-heidelberg.de
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Abstract |
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Background and Purpose— Little is known about the relevance of age related white matter lesions (WMLs) concerning outcome after first-ever territorial stroke. Based on an index patient, we hypothesized that age and pre-existent WMLs rather than infarct volume and topography determine outcome.
Patients and Methods— Thirty-four consecutive patients with magnetic resonance diffusion-weighted imaging–proven isolated acute cerebellar infarction were prospectively entered on our stroke data registry. Patients with pre-existent neurological deficits, hemorrhagic, or malignant cerebellar infarction were excluded. Patients were stratified using Rankin and Barthel disability scales into groups: I complete recovery, II moderate, and III significant disability 14 days after stroke onset.
Results— Initial neurological and functional scores were similar among all the groups with vertigo, nausea, unsteadiness, and limb ataxia being the most common. Infarct volume, vascular territories, and comorbidity did not predict clinical outcome. In contrast, presence and severity of supratentorial WMLs and age significantly determined outcome by functional tests.
Conclusions— In patients with isolated cerebellar infarction functional outcome correlated with the coexistence of age-related WMLs rather than stroke volume and topography. This reflects the loss of compensatory network integrity as the equivalent of functional incapacity beyond local lesion disturbances.
Key Words: aging • outcome • stroke • white matter
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Introduction |
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Stroke signs and symptoms have traditionally been analyzed with regard to lesion localization, infarct size, and underlying stroke mechanism. However, more recently, based on the steadily increasing quality of acute stroke imaging, the concept of an immediate relationship of clinical signs and expected anatomical lesion sites is often challenged in patients with multiple lesions. In this context, several situations are principally conceivable: (1) The synchronous occurrence of acute lesions in nonadjacent cerebral territories may cause syndromes such as "hemianopia–hemiplegia" in patients with double infarct in 1 hemisphere.1 Here, symptoms are consistent with anatomically related function, and unusual findings result from simultaneous infarction in distant vascular territories; (2) the synchronous occurrence of acute lesions in anatomically and functionally related regions either adjacent or remote but symmetrically resulting in more severe deficits than might be expected from the simple addition of 2 infarct syndromes2; (3) unexpected symptoms in the context of an acute infarct, a situation reported previously as synergistic infarct. In a published case,3 a posterior cortical infarct (aggravated in a patient with a previous frontal lesion) elicited frontal features that had not been expected from a simple sum of effect of these lesions. In a series,4 a patient exhibited clinical deterioration with a subcortical pattern of deficits fitting with his chronic lacunar lesions rather than with the acute cortical infarct; (4) an acute lesion in exact anatomical symmetry to a previous lesion in the contralateral hemisphere that may induce the reappearance of the previous deficit in addition to the newly acquired symptoms.5 Thus, concepts of remote network mediated lesions were within reach.
In light of these observations, the hypothesis was promoted that new lesions may generate symptoms unrelated to the specific anatomic or functional area affected through the breakdown of widespread neuronal networks. Patients with isolated cerebellar stroke could be considered an ideal model to test whether a disruption of the cerebellar gating function with its influence on supratentorial networks predicts functional outcome. Pre-existing supratentorial white matter lesions (WMLs) could then be considered vice versa to account for a poor prognosis in isolated cerebellar infarction. In consistence with this model, anatomical–functional networks have been proposed for a long time and (pre) frontal–subcortical circuits have been established. Recently, growing evidence from primate studies confirm the existence of vast anatomical–functional circuits through transneuronal transport of neurotropic viruses, additionally integrating cerebellar nuclei.6 Following this model, the persistence of vivid bypasses explains well sudden deterioration in morphologically insignificant network destruction and asymptomatic progress of lesion burden.
The detection of subcortical WMLs on MRI in the healthy elderly is common. Its prevalence is estimated from 5% to 20% in several population-based trials.7–9 Increasing age and vascular risk factors such as hypertension, diabetes, and hyperhomocysteinemia are related to the degree of WMLs.10,11 The clinical relevance of WMLs is controversial; however, recent data confirm the coexistence of vascular dementia, gait unsteadiness, and urinary incontinence subsumed in the syndrome of subcortical vascular encephalopathy (SVE) with severe WMLs.12 There is growing evidence that the progression of WMLs is associated with progressive functional deficits such as gait disturbance13 and upper limb discoordination,14 and a large ongoing European trial15 intends to clarify the issue of increasing disability in the elderly on the basis of progressive WMLs.
Isolated cerebellar infarcts are well characterized in prospective and retrospective studies with regard to symptoms,16–18 territories,19–21 and etiology.16 Outcome has been studied on a long-term basis in patients with stroke of the posterior circulation in general18,22,23 subgroups of acute malignant or hemorrhagic infarctions of the cerebellum,24 and has been identified in severely disabled patients.23 Thus, little is known about acute deficits resulting from loss of cerebellar tissue only. Because acute and chronic lesions in remote infratentorial and supratentorial territories can readily be identified on diffusion-weighted imaging (DWI) and T2-weighted MRI (particularly fluid-attenuated inversion recovery [FLAIR]), prerequisites are available to test our hypothesis in an acute cerebellar stroke for the first time: based on clinical observations, indicating favorable and bad outcome in morphologically similar cerebellar lesions, we hypothesized that age-related WMLs affecting the neuronal network, as represented by supratentorial white matter (WM) structures, might modulate functional outcome and define the individual outcome as well as prognosis rather than the acute infarct for sudden failure of unestablished compensatory synergistic mechanisms.
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Patients and Methods |
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Thirty-four patients (16 women, ranging from 23 to 88 years of age) with magnetic resonance (MR) DWI–proven isolated cerebellar infarction were identified of 275 consecutive patients with posterior circulation stroke diagnosed and documented according to standardized criteria in the Mannheim Stroke Registry within 4 years (1998 to 2002). Exclusion criteria were pre-existing neurological deficits, extracerebellar acute infarctions (particularly brain stem affection), and malignant or hemorrhagic cerebellar lesions. Patients were stratified by Rankin and Barthel disability scales into the following 3 groups: (1) full recovery without persistent deficit 2 days after stroke onset; (2) moderate disability (Rankin <2; Barthel >80) 14 days after stroke onset; and (3) significant disability (Rankin >2; Barthel <80) 14 days after stroke onset.
Because outcome might be strongly affected by non-neurological disease, we used the Charlson comorbidity index25 to rule out significant bias. This validated instrument assigns a weighted score from 0 to 6 to each patient reflecting the number and severity of prespecified comorbid medical conditions (ie, cardiovascular, cerebrovascular, pulmonary, endocrine, renal, and malignant diseases) and is based on the adjusted mortality risk associated with each comorbid diagnosis; it is a strong predictor of 1-year survival after hospitalization.
Stroke imaging in this study was performed on a 1.5-T magnetom vision (Siemens) for 24 to 48 hours after symptom onset and included standard T2, DWI, FLAIR, and MR angiography. MRI was read and evaluated by an independent experienced reader blinded to the clinical outcome. Apart from the identification of pre-existent cerebral lesions, small vessel changes of supratentorial subcortical WM were determined and classified by prominent features such as lesion extent, rims, and frontal caps, from none to severe according to the classification of Fazekas.26 Cerebellar infarcts were categorized according to the vascular territories as published by Tatu.20 Infarct volume was measured on DWI after template-based normalization with SPM 99.27 The image was then read by software (MCID; Imaging Research), and a semiautomatic border based on intensity differences outlined the lesion. This was done for each of the adjacent slices that were calculated, resulting in normalized total cerebellar lesion volume.
Statistics
Results are expressed as the mean±SD. Error probabilities were calculated by comparing 2 patient groups using the Mann—Whitney U test and were intended for exploratory data analysis because no Bonferroni correction was performed. The 
2 test was used for multiple categorical comparisons. Logistic regression was used to perform a prediction of dichotomous variables from interval or categorical data.
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Results |
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Of the 34 patients included, 8 patients fulfilled the criteria of group I, 20 of group II, and 6 of group III (Table 1). Clinical symptoms leading to presentation were vertigo (91%), nausea (68%), unsteadiness (68%), and limb ataxia (62%; Table 1). There was no correlation between initial symptoms and outcome and no difference between the frequency of specific symptoms between groups. Symptoms persisting after 2 weeks were mainly vertigo, dysarthria, and unsteadiness. Barthel, Rankin, and National Institutes of Health Stroke Scale (NIHSS) results measured 2 weeks after stroke onset are given in Table 2. Clinical scores at presentation were significantly worse in group III compared with group I, whereas in group II, only the Rankin and NIHSS scores were worse than in group I (P<0.01). Patients in group III were significantly older than the patients in group I; however, there was a large overlap. Comorbidity, as described by the Charlson comorbidity index, was low in all groups and not significantly different (Table 3).
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The majority of infarctions included the posterior inferior cerebellar artery territory, and >1 territory was affected in 7 patients (Table 1). Distribution of the infarct territories between the groups was similar. This was particularly true for superior cerebellar artery (SCA) infarctions. There was no significant difference in infarct size among the groups; however, there was a trend toward larger infarct volumes in group III (P<0.08; Table 3). Silent territorial infarctions were detected in 6 patients only, again with no intergroup difference.
General vascular risk factors and hypertension in particular were much more frequent in group II (>50%) and group III (100%), with large vessel disease being the suggested etiology of the acute stroke in most of the cases, whereas cardiac embolism (atrial fibrillation, patent foramen ovale) was the leading etiology of stroke in group I (Table 1).
However, subcortical WM changes were more frequent in patients with worse outcome: whereas no patient in group I exhibited any WMLs, 7 patients in group II and all of the patients in group III showed subcortical damage (Table 4). Severity of WM damage itself was not identical in groups II and III: mild (grade I) and moderate (grade II) WMLs were each present in 10% of the patients of group II; in group III, half of the patients had moderate (grade II) and the other 50% severe (grade III) WM damage. The overall frequency of WMLs was significantly higher in groups II and III compared with group I (2; P<0.01 and 0.05, respectively). There was a high correlation between the detection and the degree of WML load and the age of patients (r=0.65; P<0.001). Age also predicted patients’ group assignment (r=0.41; P<0.05). In a logistic regression combining moderate (group II) and severe persistent disability after 14 days (group III), early recovery (group I) was predicted by the absence of WMLs (Z score 5.591; P<0.018) to a slightly higher degree compared with lower age (Z score 4.514; P<0.034). In a multivariate regressional analysis identifying age and WML-associated initial symptoms, only unsteadiness was predicted by patients’ older age (t=2.52; P<0.021) and by the detection and degree of WMLs (t=2.90; P<0.007). Imaging examples characteristic for each group are shown in the Figure (A through F).
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Discussion |
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TopAbstractIntroductionPatients and MethodsResultsDiscussionReferences |
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This study presents a second level analysis of the prospective Mannheim Stroke Registry, with data on 34 highly selected patients with acute isolated cerebellar infarction. Except for patients’ age, which cannot be seen as an illness in itself, there is no significant role for comorbidity, the number of cerebellar territories affected, pre-existent silent territorial strokes, or cerebellar infarct size in the prediction of early outcome after first-ever cerebellar stroke. However, the presence and degree of subcortical WM damage was a strong predictor of early recovery. None of the 8 patients experiencing complete clinical restitution within 48 hours after stroke onset exhibited any WMLs. However, 35% of the patients in group II and all of the patients in group III had mild to severe WMLs that were not associated with any clinically apparent neurological deficits before the acute cerebellar stroke. Strongly correlated with the presence of subcortical changes, outcome in these patients was significantly worse, with WMLs being a slightly stronger predictor of nonbeneficial outcome than age.
Apart from age, the presence of WMLs was well matched by the identification of vascular risk factors: none of the patients of group I were experiencing hypertension, 50% in group II, and all of the patients in group III. Other vascular risk factors such as diabetes, hyperlipidemia, smoking, and hyperhomocysteinemia were distributed similarly between the 3 groups. Although stroke etiology differs among groups, we did not consider this to be a relevant parameter for outcome in this specific model. Whereas in the study of Kelly et al,23 the Charlson comorbidity index did significantly predict long-term outcome, no such association was seen in our study population. Therefore, the degree of subcortical damage seems to be a major factor determining recovery from acute cerebellar lesions, suggesting a mutual compensatory function of the cerebellum for progressive vascular damage to functional neuronal networks as hypothesized in SVE.
SVE is a clinical entity that, apart from the presence of WMLs, comprises several clinical features such as gait disturbance, dementia, and urinary incontinence. The fact that isolated cerebellar infarctions in general have a good functional outcome compared with infarctions in other vascular territories is also well established.17,23,24,28,29 To our knowledge, no study has investigated the association of WMLs with acute cerebellar stroke and vice versa with regard to functional outcome. With regard to supratentorial lesions, Boon et al identified the presence of silent subcortical infarcts and its relation to outcome after acute supratentorial stroke. However, they found no influence of subcortical damage to the degree of initial handicap, 30-day fatality and 1-year mortality.30
To our understanding, the mechanisms underlying the persistence of neurological deficits, namely vertigo, dysarthria, and unsteadiness after acute cerebellar infarcts in patients with WM disease, are related to pre-existing network disruption. Such missing compensation is evident for the motor loops (the cerebellum receiving information from the cerebral cortex via pontine nuclei31 and cerebellar efferences projecting to the primary motor cortices via the ventrolateral thalamus31,32 as part of a feedback control33) and their control: in SVE, the disturbance of the circuitry from frontal and parietal cortex to the basal ganglia via WM tracts causes disturbance of gait,13 disconnecting supplementary motor cortex, and therefore planning and initiating of locomotion from basal ganglia by multilocular diffuse network destruction. Considering the known complexity of motor circuits, the concept of synergistic lesions is very appealing. However, the proof of single lesions and their network disruptions is rarely described, comprising of only a few patients.3–5 One of the few established concepts of remote effects is the crossed cerebellar diaschisis, which is defined as depression of blood flow and metabolism in the cerebellar hemisphere contralateral to the focal supratentorial lesion.34 First observed in positron emission tomography, the phenomenon has been confirmed by means of functional MRI.35 Although mutual aspects of crossed cerebellar diaschisis are evident, no study has identified primarily infratentorial lesions.
Despite the limited absolute number of patients recruited in a monocenter study from a large stroke population reflecting the high degree of selection and exclusion criteria, these data support our hypothesis of a network concept for stroke prognosis. WMLs were a strong predictor of the persistence of symptoms such as vertigo, dysarthria, and unsteadiness after 14 days; this was independent of infarct size or territory of the acute cerebellar infarct but highly correlated with age. These unspecific clinical signs can be secondary to various pathologies, both non-neurological disorders (acid base disturbance, endocrinological or cardiological problems, etc) and multilocular neurological disease (supratentorial and infratentorial, subcortical and cortical, left and right hemispheric). This nonfocal character suggests an important function of subcortical relay stations and connecting fibers to compensate for cerebellar lesions evidenced by loss of network compensation in age-related WM disease. If the prevention or treatment of WMLs could be shown to be associated with risk factor modulation, this would have an important impact on the burden of stroke-associated disability.
Received February 21, 2005; revision received April 17, 2005; accepted June 13, 2005.
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