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Stroke is the leading cause of disability in the industrialized world. There are approximately 750,000 new cases of stroke every year. Approximately half of the individuals who survive a stroke will suffer long-term motor impairments severe enough to cause disability or to require the assistance of others for performing activities of daily living. The immediate care is focused on minimizing the loss of brain tissue, followed by managing the cause of the stroke, management of underlying causes or risk factors (such as smoking, diabetes, high blood pressure) and prevention of new strokes.
In some 70% of cases, stroke – an interruption of blood supply to a region of the brain – is caused by a blood clot or plaque blocking the blood vessel (ischemic stroke). Other times the cause may be bleeding at that site (hemorrhagic stroke). Since 1996, the FDA has approved the use of a clot-destroying agent that may reverse some effects of ischemic stroke, known as recombinant tissue plasminogen activator (rtPA, or tPA).
Stroke rehabilitation consists primarily of physical, speech and occupational therapies. Unfortunately, many patients recover only partially from a stroke, even with the best current therapy strategies. Hence, there is a great need for new interventions to help patients recover from stroke, and we are among the groups exploring new possibilities. Several promising lines of research may lead to a neuromodulation therapy to aid stroke rehabilitation. (Clinical trials for stroke or other disorders can be found at clinicaltrials.gov or the International Standard Randomised Controlled Trial Number Register, http://www.controlled-trials.com/.)
A number of research teams are evaluating an approach known as functional electrical stimulation (FES) to see if applying a small electrical stimulus to nerves of the arms and legs during physical therapy can enhance recovery, compared to physical therapy alone. In this non-invasive method, the mild stimulation is most commonly applied with wires attached to the skin that are controlled by external units.
Meanwhile, other interventions under investigation concern the brain itself. During stroke recovery, the brain is reorganizing in a process known as plasticity. Some damaged brain tissue may recover or undamaged areas can be retrained to take over some functions. Applying neurostimulation while the patient undergoes physical or speech therapy may enhance plasticity and facilitate recovery. Two non-invasive neurostimulation approaches are transcranial magnetic stimulation (TMS) and transcranial direct current stimulation (tDCS). Both methods do not require surgery and are applied externally to the patient’s head. In TMS, a coil is positioned over the head, typically while the patient is sitting on a special armchair. Pulses of magnetic stimulation are applied to the head at rest or during the performance of a task. These pulses may be applied on the side of the brain that has been affected by the stroke, on the side opposite to the stroke or on both sides. In tDCS, a sticker is applied to the head and is connected to a power source that creates small electrical fields. Unlike TMS, patients having tDCS can be mobile and may use the stimulation for prolonged periods of time (i.e. weeks). The stimulation can be continually delivered and patients take the devices home or to outpatient physical therapy.
Other neurostimulation approaches are invasive. In this case, a surgical procedure is done to implant a device that stimulates either the surface of the brain, just beneath the skull, or inside the brain, to influence function of neural circuits that impact the condition. Cortical stimulation (at the surface of the brain) has been studied to see if stimulation to the motor cortex enhances the results of physical therapy after stroke. Initially promising results were not borne out in a controlled clinical trial that concluded in 2008 without demonstrating a significant advantage to using motor cortex stimulation during physical therapy, although this approach’s potential may be re-examined.
Deep brain stimulation (DBS), meanwhile, is often referred to as a “brain pacemaker”. Indeed, it consists of wires implanted deep in the brain, connected to a device in the chest that looks and operates similarly to a pacemaker, sending electrical signals to the area of the brain that has been implanted with the wires. DBS is currently approved by the FDA for managing the symptoms of Parkinson’s disease, tremor, dystonia and (as a humanitarian device exception) obsessive-compulsive disorder.Finally, a minimally invasive method, peripheral nerve stimulation (PNS), has also been investigated by some groups to manage limb pain following stroke by modifying the perception of chronic pain. PNS applies a mild electric current through electrical contacts placed beneath the skin, stimulating selected peripheral nerves located beyond the brain or spinal column.
Reviewed July 31, 2012
|Last Updated on Thursday, October 17, 2013 03:32 PM|