Upper limb paresis is one of the most frequent and persistent impairments following stroke. Only 12–34% of stroke patients achieve full recovery of upper limb functioning, which seems to be required to habitually use the affected arm in daily tasks. Although the recovery of upper limb functioning is most pronounced during the first 4 weeks post stroke, there are few studies investigating the effect of rehabilitation during this critical time window. The purpose of this trial is to determine the effect of electrical somatosensory stimulation (ESS) initiated in the acute stroke phase on the recovery of upper limb functioning in a nonselected sample of stroke patients.
A sample of 102 patients with upper limb paresis of varying degrees of severity is assigned to either the intervention or the control group using stratified random sampling. The intervention group receives ESS plus usual rehabilitation and the control group receives sham ESS plus usual rehabilitation. The intervention is applied as 1 h of ESS/sham ESS daily, followed by motor training of the affected upper limb. The ESS/sham ESS treatment is initiated within 7 days from stroke onset and it is delivered during hospitalization, but no longer than 4 weeks post stroke. The primary outcome is hand dexterity assessed by the Box and Block Test; secondary outcomes are the Fugl-Meyer Assessment, hand grip strength, pinch strength, perceptual threshold of touch, degree of pain, and modified Rankin Scale score. Outcome measurements are conducted at baseline, post intervention and at 6-month follow-up.
Because of the wide inclusion criteria, we believe that the results can be generalized to the larger population of patients with a first-ever stroke who present with an upper limb paresis of varying severity. On the other hand, the sample size (n = 102) may preclude subgroup analyses in such a heterogeneous sample. The sham ESS treatment totals a mere 2% of the active ESS treatment delivered to the intervention group per ESS session, and we consider that this dose is too small to induce a treatment effect.
Stroke is ranked as the third largest cause of disease burden globally , causing substantial physical, psychological and financial demands on patients, families, and societies at large [2, 3, 4]. Upper limb paresis is one of the most frequent impairments following stroke and affects 48–77% of patients in the acute stroke phase [5, 6, 7]. Moreover, upper limb paresis has been identified as a major obstacle to regaining independence in activities of daily living (ADLs) . In fact, only 12–34% of the patients achieve full functional recovery of the affected upper limb at 6 months post stroke [9, 10]. This represents a considerable challenge since near complete functional recovery is required to routinely involve the affected upper limb in performing ADLs .
Recovery of upper limb functioning is typically pronounced during the first month and subsequently levels off by 6 months post stroke [12, 13, 14]. Regaining hand dexterity (i.e., motor skills such as reaching, grasping, gripping, moving and releasing objects) is often achieved already within the first 4 weeks, implying that there may be a critical time window for recovery of upper limb functioning [9, 10] during which rehabilitation efforts may maximize functional recovery. However, there are few studies investigating the effect of motor rehabilitation methods in the initial weeks after stroke.
Electrical stimulation (ES) is one of the methods that have been used to facilitate recovery of upper limb functioning following stroke. ES can induce a muscle contraction, or it can be a somatosensory stimulation below the motor threshold . The majority of studies using ES have been conducted in chronic stroke and, therefore, it remains unknown to what extent ES applied in the acute phase after stroke could affect the recovery of upper limb functioning. Also, these investigations have largely focused on ES that induces muscle contraction. In healthy persons, the application of low-intensity ES with no or small motor responses to peripheral hand nerves [16, 17, 18, 19, 20], forearm muscles  or the whole hand [22, 23] elicits an increase in the cortical excitability of the representations that control the stimulated body parts, which seems to outlast the stimulation period itself [18, 21, 23]. It has been hypothesized that increasing the amount of somatosensory input may enhance the motor recovery of patients following stroke . Recent data on acute, subacute and mostly chronic stroke patients suggest that a single 2-h session of ESS to the peripheral hand nerves leads to transient improvement of pinch force, movement kinematics and upper limb motor skills required for ADL performance [25, 26, 27, 28, 29, 30, 31]. However, ESS was only used in conjunction with motor training in one of these studies . Interestingly, there is some evidence that multiple sessions of ESS to the peripheral hand nerves, in conjunction with motor training, might improve motor skills of the paretic upper limb in subacute [32, 33] and chronic stroke patients , and, moreover, that these positive results seems to be long lasting . However, the effect of ESS in conjunction with motor training has never been investigated in acute stroke patients. It is noteworthy that ESS is benign in nature, causes patients minimal discomfort and adverse effects (itch and blushing), is relatively inexpensive and can easily be incorporated into clinical practice . Therefore, it would be valuable to establish the effect of multiple sessions of ESS in conjunction with motor training in the restoration of upper limb functioning in the acute stroke phase.
Does ESS treatment: (a) reduce motor and sensory impairments, (b) improve hand dexterity and (c) reduce disability at the end of the intervention period (short-term effect)?
Are the changes that can be observed at the end of the intervention period still present or improved at 6 months post stroke (long-term effect)?
Our hypothesis is that ESS treatment initiated in the acute stroke phase will improve paretic upper limb functioning as measured by the Box and Block Test (BBT) (primary outcome measure) at 6 months post stroke.