According to research, pain is one of the most common symptoms with which patients seek medical help. One particular type of pain is neuropathic pain, which affects up to 10% of the general population. Compared to musculoskeletal pain, it is usually more severe, has a greater impact on functioning, and is only partially relieved by pharmacological treatment in 30-40% of patients.
As defined by the International Association for the Study of Pain, neuropathic pain results from damage to the somatosensory part of the nervous system. It arises from neuroplastic changes that occur as a result of dysregulation within the central, peripheral and/or autonomic nervous system. These abnormalities include nerve cell hyperactivity, peripheral and central sensitization, inflammatory neurogenic edema, damage to pain control systems, and the formation of pathological connections between different types of nerve fibers. The most common causes of neuropathic pain are a history of smallpox and hemiplegic virus infection (hemiplegic neuralgia) and nervous system damage as a complication of diabetes mellitus (diabetic neuropathy). Other causes of dysregulation of the nervous system leading to neuropathic pain can be trauma (phantom pain, neuropathic postoperative pain), stroke, compression, or autoimmune diseases. Depending on the neuroanatomical location, neuropathic pain can occur in different regions of the body.
Different types of pain
Neuropathic pain can be sharp, piercing, stabbing, but it is not always felt as "pain". It can have the form of burning, tingling, sensation of "electric shock" or feeling of severe cold. Such phenomena are also characteristic:
- allodynia - painful sensation of stimuli that in healthy people do not evoke a pain reaction (e.g. heat, touch, pressure)
- hyperalgesia - increased pain sensation in response to a stimulus that in healthy individuals causes pain of low intensity (e.g. a sting),
- hyperpathia - a delayed, very intense reaction to any pain stimulus.
Pharmacotherapy of neuropathic pain includes some antidepressants and antiepileptic drugs, topical medications, followed by opioids and cannabinoids. Studies also indicate a beneficial effect of ketamine, which, as an NMDA receptor antagonist, prevents the development of central hypersensitivity and reduces the intensity of pain sensations. Transcranial magnetic stimulation (TMS) in the motor cortex stimulation protocol has also documented efficacy in the treatment of neuropathic pain. By affecting neuronal pathways connecting different regions of the nervous system, including the thalamus and spinal cord, TMS influences the activity of pain modulating systems that are associated with emotion, attention, and differentiation of sensory stimuli. It also affects neurotransmitter systems important in pain control, such as endogenous opioids, glutamate, GABA and dopamine.
Studies have shown that the application of high-frequency repetitive transcranial magnetic stimulation to the region of primary motor representation on the side opposite to the region of the body where the pain is felt can completely and permanently eliminate symptoms in up to 80% of patients.