Herpes zoster is a viral skin disease characterized by clusters of herpes and neuralgia along the nerves caused by varicella-zoster virus infection. In Chinese medicine, it is known as “tangled waist fire dragon” and “tangled waist fire dan”. It is also commonly known as “snake sores” and “spider sores”. Neuralgia is an important feature of the disease, and some patients still have neuralgia at the site of invasion after the herpes has subsided, which may last for months or even years, called postherpetic neuralgia. Approximately 10% of patients with herpes zoster can have postherpetic neuralgia, and its incidence is proportional to age, ranging from 49% at age 50-59, 65% at age 60-69, and 74% at age 70-79. That is, the older the age, the more likely it is that postherpetic neuralgia occurs, so it is more frequent in the elderly. Our elderly population is increasing, and the incidence of postherpetic neuralgia continues to increase. It is difficult to treat the pain effectively, and the patients suffer from the pain for a long time, not only are they depressed and have a low quality of life, but they are also depressed, lose confidence in life, and even have suicidal tendencies. Some people call this pain “the first pain in the world”. Therefore, it is necessary to seize the best time to treat this disease.
Pathogenesis.
Herpes zoster has been around for a long time, but it was not understood to be a viral disease until the late nineteenth century. We now know that the varicella-zoster virus invades the body through the sensory nerve endings of the skin and then enters the ganglion cells of the posterior roots of the crestal nerves in a dormant state. When the normal immune defense mechanisms of the body are damaged or suppressed, the varicella-zoster virus is activated and the disease develops. The exact pathogenesis of postherpetic neuralgia is not fully understood, but is associated with the following factors: older age; herpes virus infection; patient’s immune deficiency; patient’s idiosyncratic constitution; untimely treatment after herpes zoster; and lack of aggressive nerve block treatment even though antiviral therapy is administered.
Pathological changes.
The duration of postherpetic neuralgia is usually about 2-5 years, and the pathological changes concerning it are not fully understood. Although its pain is associated with the herpes virus, they are considered to be two different types of pain of different nature. It has been documented that patients with postherpetic neuralgia have atrophy of the infected side of the dorsal horn and lesions in the sensory ganglia. In patients with postherpetic neuralgia, the nervous system is extensively and severely damaged by the herpes virus, with not only dehydration, Wallerian degeneration, marked cystic degeneration, and a significant decrease in the number of ganglion neurons in the crista posterior radicular ganglion, but also a decrease in axons and marked collagenization of peripheral nerves, especially the myelinated thick nerve fibers, and chronic inflammatory cells in the crista posterior radicular ganglion. There is also chronic inflammatory cell infiltration in the posterior crista root ganglion. The patient has significant degenerative changes in the dorsal horn of the crista medullaris. Imaging and autopsy studies also reveal significant atrophy of the dorsal horn of the crista medullaris.
Autopsy studies also demonstrate a significant pericristal inflammatory response in patients with a long course of disease, with a high concentration of lymphocytes and degenerative changes in the dorsal horn of the crista and the posterior root ganglion of the crista. In contrast, no significant central nervous system changes were found in patients with full recovery. The pain mechanism of postherpetic neuralgia involves ectopic discharge of injured peripheral afferent fibers, cross-mixing of neurons, sensitization of neurons in the dorsal horn of the crista medullaris, and decreased function of inhibitory neurons in the crista medullaris.
Clinical manifestations and features.
Postherpetic neuralgia is a persistent pain that plagues middle-aged and elderly people, and its duration can be as short as 1-2 years or as long as 10 years or even more than decades in some cases. The nerve most commonly involved in herpes zoster is the intercostal nerve, accounting for more than 70% of the total number of cases; the next nerves involved are the trigeminal nerve, sciatic nerve, and less frequently the cervical nerve, brachial plexus nerve, and pubic nerve, etc. Basically, the nerves invaded are sensory nerves, and there is almost no effect on motor nerve fibers. When the acute phase of the rash heals, the lesioned skin often appears red, purple or brown. After the color disappears, a grayish-white scar is often left behind, or sometimes severe pain can occur without scarring remains. The scarred area generally shows hyperalgesia and often loss of sensation, but stimulation by touch often causes significant superficial tissue pain (abnormal pain, commonly known as tenderness), and injurious stimuli may cause increased pain or increased sensitivity to touch. The patient’s pain often appears as spontaneous lightning-like or tearing pain that can be exacerbated by contact with the lesioned skin, such as extremely light clothing friction. The nature of the pain is predominantly spontaneous slash-like or lightning-like episodes of pain or persistent burning pain, with most patients experiencing intolerable levels of pain. The majority of patients exhibit nociceptive hypersensitivity, producing unbearable pain with light touch, and some patients are characterized by hyperalgesia. In addition to this, it can be aggravated by physical activity, temperature changes and emotional depression. Due to the fear of severe pain, patients are psychologically burdened, depressed and prone to psychological problems.
Treatment.
Conventional analgesic treatment is less effective. At present, most advocate a combination of oral drugs, intradermal injection and nerve block as a comprehensive therapy, which can achieve satisfactory results.
(1) Early antiviral treatment is very important, antiviral drugs include: acyclovir, valacyclovir, etc.
(2) Pharmacological treatment: The international guidelines suggest that tricyclic antidepressants, antiepileptic drugs and lidocaine patches are the first-line drugs, opioids and tramadol are the second-line drugs, and capsaicin patches and sodium valproate (Depakene) are the third-line drugs. In recent years, gabapentin and pregabalin have been used to treat postherpetic neuralgia with good efficacy.
(3) Intradermal injection: local anesthetics are injected into the tissue of the lesion area to block the nerve endings and achieve anesthesia. Lidocaine and other local anesthetics can block the pain transmission of sensory fibers, interrupting the vicious cycle of pain, and also blocking the reflex sympathetic nervous system hyperactivity, prompting local vasodilation, improving blood flow, and promoting tissue function recovery. This method is a new treatment method recently promoted with satisfactory effect, simple and easy, safe and with few side effects.
(4) Nerve block: according to the site of pain, peripheral nerve block, stellate ganglion block or epidural block can be used. It is one of the most effective treatment methods. As long as there is no obvious local infection, the injection of the identified infringing nerve trunk can play the role of pain relief, improve local blood circulation, anti-infection, increase the speed of healing of skin lesions and reduce sequelae.
(5) Electrophysiology and neuromodulation: The principle of this method is to stimulate the target nerve that can produce pain through electrodes appropriately, thus producing numbness-like sensation to cover the painful area, so as to achieve pain relief, mainly divided into transcutaneous nerve electrical stimulation, peripheral nerve stimulation, cremaster electrical stimulation, etc.
(6) For patients with stubborn pain, when the effect of various methods is not good or cannot be maintained, and when the effect of motor nerve block does not affect the patient much, nerve destruction injection can be used, such as: intercostal nerve, trigeminal nerve, cervical nerve, etc. It is mainly divided into chemical and physical methods. Alcohol, phenol glycerin and phenol are the commonly used chemical destruction drugs but must be operated by an experienced pain physician or anesthesiologist, otherwise it can lead to serious consequences.
(7) Postherpetic neuralgia nerve damage repair is very difficult and the treatment process is long. In recent years, nerve growth factor and neurotrophic factor have been used clinically to play an active role in the repair process of the damaged nerve fibers.
Prevention.
(1) Live a regular life, eat a nutritious diet, be in a relaxed mood, adhere to physical exercise, enhance physical fitness and improve your immune system.
(2) Once herpes zoster is diagnosed, receive regular treatment as soon as possible to avoid delaying the disease. In the early stage of acute herpes zoster, nerve block treatment is performed, which not only has a precise analgesic effect, but also can significantly improve local blood circulation, accelerate the healing of the lesion rash and prevent the occurrence of post-acute herpes zoster neuralgia.
(3) In the acute herpes zoster phase, apply comprehensive treatment, early application of antiviral, corticosteroid and anti-inflammatory analgesic drugs, and early analgesic treatment to prevent central sensitization of pain. Strive for a complete cure.
(4) Prophylactic injection of live attenuated varicella virus vaccine, or varicella-zoster virus immunoglobulin.