Pain treatment as an emerging specialty was developed in the 1970s in countries all over the world, especially in the United States, Japan, and Western Europe, etc. The International Society for the Study of Pain was established in 1975, and the journal Pain was published in the same year. In the early 1980s, pain treatment clinics and wards were opened in China.
In September 1988, the Pain Treatment Specialty Group of the Society of Anesthesiology of the Chinese Medical Association was established, and in September 1989, the Chinese Society for the Study of Pain (CASP) was established. Three professional journals, Chinese Journal of Pain Medicine, Chinese Anesthesia and Analgesia and Pain, have been published one after another. In 2007, the Ministry of Health of China issued a special document No. 227, which added the first-level medical subject “Pain Medicine” to the “List of Medical Institutions”, with the code “27”, and clarified that the main scope of “Pain Medicine The main scope of business of “pain department” is: diagnosis and treatment of chronic pain. As a kind of chronic pain, neuropathic pain has the complexity of mechanism and the difficulty of treatment.
Clinical manifestations and characteristics of neuropathic pain
I. Nature of neuropathic pain
Neuropathic pain is the pain caused by primary damage to the peripheral or central nervous system, which has its own unique nature and characteristics, often manifested as lightning-like, gunshot-like, squeezing-like, pinprick-like, knife-like, tearing-like, burning-like, pulling-like, taut-like, pressure-like and insect bite-like pain, and sometimes even just itching or some other uncomfortable sensations.
The nature of neuropathic pain is variable and unclear, and the degree of pain varies. The nature of pain in peripheral neuralgia is pins and needles, electric shock or burning sensation, some transient and intense, some diffuse and persistent, and may be manifested as nociceptive hypersensitivity, touch-evoked pain, etc. Central pain is similar in nature to non-afferent pain due to peripheral nerve damage and is often described by patients as persistent dull pain, paresthesia, burning pain, or a tightening sensation in the girdle. The nature of the pain is relatively constant, sometimes with transient episodes of acute pain of a cut-like or electric shock-like nature, and the pain is mostly moderate to severe, even unbearable, and may be altered in distribution. It is unclear whether the nature of central pain differs between patients with complete and incomplete spinal cord injury. Patients with spinal cord injury described their central pain on the McGill Pain Questionnaire in 57% of cases with knife-like pain and 47% of cases with burning pain. There are individual differences in the occurrence and development of neuropathic pain, and the same damage does not necessarily cause pain in every individual.
The site of neuropathic pain is determined by the location of the lesion. In most cases, the site of pain is closely related to the site of the lesion. For example, when inflammation occurs in a peripheral nerve, pain is felt in the area of distribution of that nerve, and the site of pain is consistent with the anatomical location of the nerve trunk. The patient can often specify the exact site and extent of the pain. It is worth noting that patients with peripheral neuralgia who undergo central sensitization may also experience significant changes in the site, nature, degree and extent of pain: the site of pain may be indeterminate, the nature of pain may change, the extent of pain may expand, the degree of pain may increase and spontaneous pain, nociceptive hypersensitivity, and touch-induced pain may occur, whereas central pain is more widespread and may appear on the contralateral side of the face, trunk, part of the extremities or For example, most of the spinal cord injuries can cause bilateral pain, which involves the body area innervated by the caudal segment of the lesion, and the pain in spinal cord cavitation is mostly asymmetric, limited to one upper extremity and chest, or even part of one chest, and a few patients involve unilateral lower extremity.
Generally speaking, once neuropathic pain appears, it will progressively worsen and develop gradually. The nature of the pain and the location of the pain also change constantly, and sometimes it can develop to an unimaginable degree. We have met several patients who have suffered from neuralgia after forehead and chest rash for more than 10 years, first with severe spontaneous pain in the area of herpes, and then gradually developed into generalized pain, and any environmental and emotional stimulation can induce severe and persistent pain.
Characteristics of neuropathic pain
Unlike physiological pain, neuropathic pain has no protective effect on the organism. Generally speaking, all peripheral nerve injuries bring about some degree of pain, while the occurrence and development of central pain varies individually, and the same damage does not necessarily cause pain in every patient, and the manifestation of pain varies. However, in general, neuropathic pain has its common features: spontaneous pain, nociceptive hyperalgesia, touch-induced pain, and sensory abnormalities.
(A) Spontaneous pain
Spontaneous pain (spontaneous pain) refers to spontaneous random persistent pain that does not depend on peripheral stimulation.
1.Pain site
The site of spontaneous pain is closely related to the site of the lesion. In patients with peripheral neuralgia, pain usually occurs in the damaged innervation area or sensory deficit area, and patients can often specify the exact location and extent of pain. Central neuralgia is generally difficult to localize because it can involve other parts of the body. Sometimes central pain can be seen in the whole body or half of the body, or it can involve one hand or one side.
2.Nature of pain
There are many kinds of nature of spontaneous pain, which can show stabbing pain, colic, burning pain, persistent hidden pain, tearing pain, cutting pain, crushing pain, shooting pain, throbbing pain, stinging pain, pulling pain, electric shock-like pain, etc. The nature of pain caused by different organ or tissue lesions in the body has its own characteristics. Many patients with central pain have more than one kind of pain nature, often manifesting as severe burning, cutting or discharge-like pain, and some patients prefer to receive stimulation such as limb massage when in pain. Different pains can exist in one area of the body at the same time, or in different parts of the body.
3.The onset and duration of pain
The time of onset and duration of spontaneous pain varies. The pain starts days or weeks or sometimes even months after the injury and can be sudden, persistent or intermittent. The onset of pain varies from disease to disease, such as trigeminal neuralgia, which has a sudden onset and lasts for several seconds, minutes or even hours. Peripheral nerves may present as sudden spontaneous pain lasting for several days or weeks, and sometimes months, after the injury.
The nature of the pain is varied, not always burning pain, and there are many patients who do not have spontaneous pain, which can occur only when the body moves. Some patients may still have intractable pain 3-6 months or more after the injury, and spread to the surrounding area, with increased sensation, especially tactile and temperature sensation, as well as nociceptive hypersensitivity.
4.The degree of pain
The degree of pain is influenced by a variety of factors such as individual tolerance, physical fitness, psychological quality, mental state, attention and environmental conditions. The patient’s reaction to pain varies from person to person, so the clinical evaluation of pain level is still based on the patient’s subjective description. Commonly used methods include oral grading, behavioral pain measurement, numerical scoring, multi-factor pain questionnaire, and visual analog scoring.
In general, only mild, moderate and severe pain levels are classified. Migraine and tension headache, on the other hand, mostly present as mild or moderate pain. Trigeminal neuralgia and postherpetic neuralgia may present as severe pain. However, regardless of the degree of pain, many patients consider the pain they feel to be severe.
(B) Nociceptive hypersensitivity
Nociceptive hyperalgesia (hyperalgesia) refers to pain caused by tissue injury with a reduced pain threshold and an abnormally enhanced and prolonged response to injurious stimuli, and is a manifestation of a strong response to painful stimuli; for example, a mild painful stimulus in the skin of the affected area can cause a strong painful attack, and even the stimulation of internal organs, especially the filling of the bladder and rectum, can also induce or intensify pain. According to the different mechanisms of its occurrence, it can be divided into primary and secondary nociceptive hypersensitivity. The former refers to an overreaction to mechanical and thermal stimuli from the injured area; while the latter refers to an overreaction to mechanical stimuli from the uninjured area surrounding the injured area.
Nociceptive hypersensitivity is common in patients with post-stroke central pain, and in patients with sensory loss, pinprick stimulation may cause pain of greater intensity (nociceptive hypersensitivity), but relatively weak. Clinically, many patients with peripheral and central neuropathic pain, such as postherpetic neuralgia, diabetic peripheral neuropathy, post-stroke central pain, and post-spinal cord injury disorders, may present with nociceptive hyperalgesia.
(C) Touch-evoked pain
The term allodynia was originally used to distinguish between hyperalgesia and hyperalgesia. Both conditions occur in patients with neurological injury, and pain can be triggered by touch, light pressure, or moderate cold or hot stimulation of normal skin.
Touch-induced pain has a change in the nature of the sensation, whether it is tactile, temperature or other sensations that cause pain, losing the characteristics of these sensations and, crucially, various painless stimuli that trigger painful sensations. Nociceptive hypersensitivity or sensory hypersensitivity are different in that they do not have a change in the nature of the sensation. Nociceptive hypersensitivity refers to an increase in pain sensation and sensory hypersensitivity refers to an increase in sensation including pain. It has been reported in the literature that 88% of patients with post-stroke central pain have abnormal pain to touch, which can be induced by everyday environmental stimuli. Such as light contact or pressure on the skin, light touch of sheets, underwear or fine hair, even breezes, car rides, general walking or movement of the limbs, too cold or too hot weather, etc.
Trigeminal neuralgia can occur suddenly when talking, washing, brushing, or eating and chewing. Postherpetic neuralgia can be triggered by stimulation such as touch, clothing flicking or wind blowing.
(iv) Sensory abnormalities
Sensory abnormalities (paresthesia) Superimposed pain and repetitive stimulation causing nociceptive hypersensitivity are important evidence of sensory abnormalities, especially when the original sensation is diminished. Central pain in patients with spinal cord injury varies widely in terms of sensory abnormalities, with variations ranging from mildly elevated thresholds for one sensory form to loss of all sensitivity in the painful area.
1.Sensory hypersensitivity
Sensory hypersensitivity (hypesthesia) is an increased sensitivity to stimuli that does not include specific sensations. Sensory hypersensitivity mainly refers to a variety of skin sensations, including non-painful tactile and temperature sensations and nociception. It is mostly used for reduced sensory threshold to various stimuli and increased response to normal sensory stimuli.
2.Decreased sensation
Hyperalgesia (hypoesthesia) is often characterized by an increase in sensory thresholds, which also means that the sensation induced by a stimulus is weaker than normal. Elevated sensory thresholds or loss of sensitivity are common in central pain. Patients with post-stroke central pain are hyperalgesic to temperature, while about half of the patients are hyperalgesic to touch, vibration, and motion only. 3. Sensory dullness
3. dysesthesia is a spontaneous or evoked unpleasant sensation, often induced by touch and cold stimuli, and may be severe. Sensory dysesthesia is most common in central pain. Spontaneous and evoked sensory blunting has been reported in 40% and 85% of patients with post-stroke central pain, respectively. Nociceptive sensory blunting combined with non-sensory blunted central pain is likely to cause sensory blunted pain and dominate central pain.
4.Abnormal sensation
Abnormal sensations include ant crawling sensation, numbness, itching, and tingling sensation. Many patients with central pain often complain of numbness or insect crawling sensation. This experience can occur with abnormal sensation and sensory dullness, or when the tactile threshold is normal.