tDCS Associated With Peripheral Electrical Stimulation for Pain Control in Individuals With Sickle Cell Disease

Pain, in its various manifestations, is the symptom most often associated to SCD, being responsible for over 90% of hospital admissions. Oftenly pain has a major impact on the patient's life and is associated with some degree of disability. Chronic pain may reflect the continuity of tissue injury and central nervous system maladaptive plasticity. They start with tissue injuries such as leg ulcers, avascular osteonecrosis, chronic osteomyelitis, arthropathy, or even continue after the repair process, by central nervous sensitization and / or peripheral. The lack of diagnosis in cases of chronic and neuropathic pain in patients with SCD is common, implying inappropriate use of therapeutic resources by the health services, resulting in increased suffering to the patient. The release of inflammatory mediators is related to the perception of pain, and may cause nociceptor sensitization.

The tDCS has the potential to change the neuronal membrane resting potential, this effect is dependent on the polarity, being that cathode produces hyperpolarization, whereas anode produces depolarization, in this way can induce an effect of inhibition and facilitation of neuronal firing, respectively. This effects can induces changes in cortical excitability. Although tDCS may modulate areas related to endogenous pain control, its effects seem to be diffuse, and focality would probably enhance its effects. The peripheral electrical stimulation (PES), in another way, may also modulate cortical excitability, depending mainly on its amplitude and frequency. PES modulation of cortical excitability is very focal, occurring only in the stimulated region. The combination of these two neuromodulatory techniques has showed additive effects in some studies with individuals suffering from chronic pain,which promoting a general effect (tDCS), and the other a more focal effect (TENS). Although this additive effect has been demonstrated, to date, no study evaluate its safety and efficacy in individuals with DF.

As a secondary outcome, the investigators are going to access the influence of the intervention on quantitative electroencephalography (qEEG). Growing evidence points out to different brain characteristics between individuals with chronic pain and healthy. qEEG has high temporal resolution and evaluates primary electrical effects of neural excitation, allowing identify possible patterns of brain functioning in individuals with chronic pain. qEEG allowed the identification of the thalamocortical dysrhythmia (TCD) in patients with chronic pain characterized by an increased low frequency band power density theta (4 - 7Hz) and a decrease in high frequency bands alpha (8 -12Hz) and beta (13 - 30Hz). This dysrhythmic mechanism may occur from the periphery to the thalamus (bottom-up) or cortical dysregulation (top-down), disinhibition of the thalamus. This process results in hyperpolarization of thalamic neurons, leading to a preponderance of low frequency oscillations in qEEG. The persistence thalamic firing at low frequencies can lead to a collateral inhibition in cortical regions around, which could theoretically lead to a decrease in the higher frequencies. This increase occurs at low frequency regions involved in neuro matrix of pain.

The investigators will alse avaluate the influence of the chronic pain sencondary to avascular necrosis of hip joint about cortical motor reorganization using transcranial magnetic stimuation (TMS). Recent data point to a gluteus maximus muscle weakness during maximal voluntary contraction in pronation position in individuals with joint pain in the hip. Similarly, individuals with legg calve perthes who suffer from femoral head necrosis, weakness of the abductor hip musculature was related to poor clinical outcomes. A possible explanation for these findings is cortical motor reorganization, which is associated with motor control impairment, and this has been demonstrated in individuals with chronic lateral epicondylalgia and knee osteoarthritis, where cortical organization is altered and correlated positively with the time of Pain and is associated with the perpetuation of pain. This cortical reorganization can occur in the somatotopic areas corresponding to the motor or sensorial homunculus, having as characteristic an overlap, retraction and "blurring" in the somatotopic representation of a certain region.

The mediators released by cells of the immune and inflammatory system can act directly on neurons sensitizing and enabling them (usually peripheral nociceptors or neurons in the dorsal horn of the spinal cord). There are several mediators in a long and growing list that includes cytokines and neurotrophins.The major cytokines in an acute inflammation are the Tumor Necrosis Factor (TNF) and the interleukins (IL-1), IL-6 and IL-8, which are important mediators of acute and chronic inflammatory reactions, as well as processes of repair and resolution. High serum levels of IL-8 have been observed in patients in vase-occlusive crisis, important clinical aspect of the pathogenesis of SCD. The presence of the mutant allele A appears to influence the expression of the TNF-alpha, being the AA genotype considered a high producer.

Neurotrophins are dimeric proteins that are essential for the normal development of the nervous system in vertebrates. This family includes the nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF) and other neurotrophins (NT). Currently, it is recognized that certain neurotrophins, particularly the NGF and the brain-derived neurotrophic factor BDNF play a significant role in nociception, so that the NGF sensitizes nociceptors at the periphery, while the BDNF enhances the response ability of the dorsal horn neurons of the spinal cord. The BDNF gene, which encodes the BDNF protein, located on chromosome 11 at the boundary of regions 11p13 and 11p14 of the human genome has been investigated in a wide range of areas related to neuroplasticity, including differences in brain morphology, learning and memory, interactions with brain stimulation protocols of plasticity induction and recovery after brain injury and has been associated with a wide variety of neurological disorders, including, for example, depression, schizophrenia and attention deficit hyperactivity disorder (ADHD).