Stroke is a disease with a high social impact causing high mortality and severe residual disability. In particular, during the acute phase it is difficult to assess the patient’s functional prognosis, especially with regard to the motor deficits that impair the activity in daily life [
1,
2]. After a stroke, hemiparesis is the most common residual disability with a wide range of severity, having the upper limb the lowest functional recovery [
3‐
5]. During the acute phase, tracking the motor performance variations of the affected upper limb versus the unaffected arm could be useful to measure clinical severity over time and to formulate a prognosis. Nowadays, the stroke unit represents the gold standard in the management of the acute stroke, since it provides a continuous multi-parametric monitoring that allows the identification of changes in cardiac functioning, blood pressure levels and hematic oxygen saturation. At the moment, the continuous monitoring of motor deficit is not implemented in the stroke unit environment. Actigraphy allows the long-term assessment of the patient’s wrist movements by means of a small solid-state sensor. Several applications of actigraphy based on accelerometers have been proposed. Indeed, actigraphy has proved its usefulness not only in sleep medicine [
6], but also in other fields, for example in Parkinson tremor quantification [
7]. So far, few papers have reported the use of actigraphy in stroke: these studies provided the first indication that actigraphy might be sensitive enough to detect changes in motor activity during the recovery process and to quantify motor activity in everyday life [
8‐
14] but, no data is available about the spontaneous upper limb motor performance in the very acute phase of stroke, when the instability of clinical picture can strongly impact on prognosis and future disability and the patient needs to be monitored in an intensive care unit. Page et al. [
15] have used actigraphy to evaluate rehabilitative therapies in subacute stroke subjects. Gubbi et al. [
16] performed short actigraphic recordings in the hyper-acute post-stroke phase and developed an algorithm capable of calculating an index equivalent to the motor subscore of the National Institutes of Health Stroke Scale (NIHSS) that is a clinical score used to monitor changes of the neurological status during the hospital stay, with a maximum of 42 (severe stroke) and a minimum of 0 (no symptoms) [
17]. The same group subsequently used that index to quantify the movement difference between arms by an intra-class correlation coefficient (ICC) analysis. They found that the greater is the difference in activity between the affected and unaffected limb, as measured by ICC, the higher is the NIHSS total score; however, they did not found any correlation between the inter-limbs motor difference and the more specific NIHSS motor sub-score [
18]. Reiterer et al. actigraphically monitored motor activity of both arms in 38 patients with transient ischemic attack, ischemic lesion or non-traumatic intracerebral haemorrhage for 24 h in four different time points: 24–36 h after symptoms onset, 5–7 days later, at 3 and 6 months after symptoms onset. They demonstrated that motor performance of paretic and not paretic limbs differ during the first two time points while in the further two time points this difference was attenuated [
19]. However, the actigraphic index used by the Authors did not correlate with the clinical severity in the acute phase as assessed by the NIHSS. Moreover, the Authors performed 24 h recordings in a very heterogeneous sample of patients (transient ischemic attack, ischemic lesion and non-traumatic intracerebral hemorrhage), therefore the reported data cannot be considered as representative of the ischemic stroke scenario. Urbin et al. investigated different metrics to measure upper limb motor performance in subacute and chronic ischemic and hemorrhagic stroke patients during motor training and in a free-living environment. They described the asymmetry of motor performance between paretic and non-paretic arm as a ratio between the variability of the paretic arm acceleration relative to variability of the non-paretic arm. They found that the asymmetry correlates with upper extremity function during the rehabilitative process and in a free-living environment [
9,
10]. Since the authors enrolled ischemic and hemorrhagic, subacute and chronic stroke patients in an environment very different from that of a stroke unit, their results, although useful to evaluate the efficacy of different parameters, cannot be considered representative of the clinical picture of ischemic stroke patients who require intensive cares in their very acute phase.
In a previous study performed in healthy subjects, Rabuffetti et al. defined a novel numerical index to quantify upper limb motor activity and the between-limb motor asymmetry. The proposed motor activity index only depends on sensor position and not on sensor orientation (i.e. indices invariant to sensor orientation), therefore it could represent a robust approach to monitor spontaneous motor performance in complex environments such as stroke units. Moreover, the proposed asymmetry index is based on epoch-based asymmetry and not on average overall asymmetry [
9,
10] therefore it could be theoretically very precise in describing motor performance over time [
20]. We hypothesized that such index might effectively track the motor behavior of bed-restrained patients and could be useful to implement the multiparametric monitoring in the stroke unit environment. Therefore the aims of the present study were:
- to verify if the actigraphic asymmetry index, as calculated by Rabuffetti, can identify the paretic arm of acute stroke patients;
- to verify if such asymmetry index can properly quantify the clinical severity of acute stroke patients in the very particular environment of a stroke unit.