Herpes Zoster (HZ) also known as Shingles, is a disease whereby the Varicella zoster virus (VZV) which had been dormant in the dorsal root ganglion or trigeminal ganglion since the initial infection with VZV, is reactivated when the human body is weakened or compromised immune system [1]. It is a disease where small vesicles appear in a band shape alongside a rash, and usually accompanied by sharp pain [1]. HZ can cause various complications such as meningitis, pneumonia, secondary bacterial infection, and postherpetic neuralgia (PHN) during or after treatment. Among them, PHN is the most common complication and is one of the causes of intractable chronic pain syndrome [2]. PHN is a condition where pain can continue for more than 1 month after the skin rash caused by the acute HZ has healed [3]. PHN can be accompanied by intermittent lancinating pain, allodynia, and persistent deep burning pain. These symptoms tend to be more unpleasant than those of HZ. In some cases, alongside the pain, there is a decrease in sensation in the skin. Chronic neuralgia can also lead to physical and emotional dysfunction, which significantly reduces the patient’s quality of life [4]. It has been reported that when the intensity of the pain was severe in patients, the prodromal symptoms before the rash were severe, and people were older, with an increased probability of transition to PHN [5]. The annual worldwide incidence of PHN is 1.5 to 4 per 1,000 people, but among those in their 60s and older, the incidence rate is 7.2 to 11.8 per 1,000 people [6]. The number of patients treated for HZ in Korea increased from 480,000 in 2010 to about 720,000 in 2020 [7]. Considering that 4–70% of patients over the age of 60 with HZ experience PHN [8], the number of patients with PHN are expected to increase accordingly. Western medicine including antidepressants, anticonvulsants, nerve blocks by topical anesthetic, sympathectomy, and intrathecal drug pump insertion, have all been used to treat PHN, however, no successful treatment has been reported so far [9]. Besides, the effectiveness of pharmacological treatment is limited [10] with satisfactory analgesia reported in approximately 50% patients [11], and these treatments may increase the incidence of adverse effects, such as sedation, xerostomia, dizziness, fatigue, and weight gain [12–14]. Thus, an effective pain management for PHN is needed [15]. It has been reported that PHN could be relieved effectively by using traditional medicine such as acupuncture, moxibustion, Chinese medicine, and cupping with bleeding for patients with PHN [16,17].

In the Korea Health Insurance Review and Assessment Institute, HZ ranked 70th in the list for frequent diseases where Korean medicine treatment (KMT) was received as inpatient treatment and 127th in outpatient treatment for patients aged 60–69 years between 2017 and 2020 [18]. However, there was not much data on the type of KMT implemented for PHN, the most common complication of HZ. For this reason, we tried to determine the status and possibility of KMT for PHN in Korea.

In this study, we reviewed Korean Medicine journals published between 2000 and 2020 and analyzed clinical research where KMT was applied to PHN. Through this, we intend to provide practically effective data to support KMT for PHN clinical treatment.

In this study, clinical research on PHN that were published between January 1, 2000, and December 31, 2020, in 5 Korean databases were analyzed. A total of 17 cases were reported in 12 studies. The studies covered 8 female cases and 9 male cases. Among all the cases, those in their 50s or older accounted for the majority with 8 female cases (100% of female cases) and 8 male cases (88.8% of total male cases). This was consistent with a previous study, which reported that 40.6% (13 men) and 39.1% (25 women) of cases had no significant gender difference in PHN outbreaks [2]. With regards to the type of PHN (according to the classification by the site of pain), thoracic pain was the most frequently observed with 13 cases (72.2%), and among them, left thoracic pain was dominant with 9 cases (52.9%). This result was also consistent with a previous study showing that the thoracic innervation area is the most commonly PHN-affected site [2].

KMT was conducted including acupuncture, herbal medicine, moxibustion, physical therapy, and together with Western medicine in some cases. Acupuncture and herbal medicine were used as the main methods for the KMT of PHN. The most frequently mentioned acupoints were GB44, LI4 and LR3. GB44 was frequently used when the pain was located in the thoracic region. In previous studies, LI4 was frequently used for acupuncture anesthesia due to its excellent pain control [31,32]. LR3 has been reported to have pain control and nerve regeneration effects [33]. In a study by Choi et al, the overseas, randomized clinical study included acupuncture treatment for acute stage HZ which reported similar results to this study, as the LI11, LR3, and ST36 acupoints were the most frequently used after the Ashi-point [34]. It can be concluded that these acupoints were also chosen to control pain in PHN.

When using pharmacopuncture, Bee venom was most frequently used, and has been reported to improve neurological disorders through anti-inflammatory, analgetic, immunomodulatory, antimicrobial, antiviral, vascular permeability, and nervous system excitatory effects of the nervous system [35,36]. In addition, Hwanglyeonhaedok injection was also used to treat PHN symptoms due to its anti-inflammatory and analgesic properties [37]. In addition, Kweon et al [24] reported the results of 5 patients who were treated with warm acupuncture [24]. It is said that the condition in which the nervous system is damaged and does not function properly due to the sequelae of HZ is similar to that of a stagnant meridian therefore, warm acupuncture treatment was applied [24]. In addition to the analgesic effect, warm acupuncture is widely used for musculoskeletal pain conditions/diseases and has been applied to various conditions/diseases because of its effect on enhancing immunity [38].

Sipjeondaebotanggami was the most frequently used herbal medicine prescription in 5 cases. It is a prescription made by adding Cinnamomi Cortex Spissus and Astragali Radix to Sagunjatang, which is mainly used for invigorating the body, and adding Samultang, which is mainly used for tonifying blood. Sipjeondaebotang has been reported to be involved with the immune response of organs of the immune system such as the bone marrow, spleen, thymus, and liver [39]. Sipjeondaebotang not only improves immune function in the body through increased activity of the bone marrow, spleen, thymus and immunoglobin, but also possesses antioxidant, antibacterial and anti-inflammatory properties [39]. Since all 5 patients who received Sipjeondaebotanggami treatment were elderly and frail, it seems that pain control was performed by adding herbal medicines (such as Olibanum and Myrrha which activate blood flow, and remove blood stasis) to Sipjeondaebotang, which has been shown to improve immune function in the body.

Yongdamsagantang was used in 3 cases. Yongdamsagantang has been reported to have antiallergic, anti-inflammatory, and antiviral properties [40]. Furthermore, it is known to have a cellular immunomodulatory effect, which is reported to alleviate inflammatory responses of HZ to control pain and rash [41]. In all 3 studies, Yongdamsagantang was prescribed at the beginning of PHN treatment. While Sipjeondaebotanggami was primarily used for elderly and feeble patients, Yongdamsagantang was used in robust patients for a relatively short period of time to relieve severe pain. It is likely that when prescribing herbal medicine for PHN, the patient’s symptoms and physical conditions are taken into consideration.

Glycyrrhizae Radix et Rhizoma was most frequently used compositional drug with a total of 21 cases of usage. Next was Poria Sclerotium, which was used 18 times, followed by Angelicae Gigantis Radix, which was used 16 times. Since Glycyrhizae Radix (being used as the harmonizer for all medicines), the most used medicine as the principal herb was Poria Sclerotium. Poria Sclerotium is an important herbal medicine that has been reported to have anti-inflammatory, antioxidant, ulcer preventing, immune-enhancing, and anti-cancerous properties [42].

According to the classification of herbal medicine [43], tonifying and replenishing medicines (16 types), heat-clearing medicines (15 types), exterior-releasing medicines (14 types), dampness draining diuretic medicines (8 types), and blood-activating and stasis-dispelling medicines (11 types) were used frequently. It is thought that the purpose of using herbal medicines such as tonifying and replenishing medicines was to strengthen the body’s immunity as HZ occurred due to the recurrence of the latent VZV and PHN appeared as a complication. Seeing that many dampness draining diuretic medicines and heat-clearing and dampness-drying medicines were used, it is probable that the etiology of PHN was regarded as dampness-phlegm and herbal medicines were used to remove it. Herbal medicines that activate blood flow and remove blood stasis are used to promote blood circulation by removing the narrowing and occlusion of blood vessels caused by peripheral circulation disorders [44]. It can be inferred that the 2 external treatments were mainly used for this effect. In terms of the dosing period, the effect of the dosing period was seen as the number of cases that had periods of less than 10 days, 11–20 days, 21–30 days, and 31–40 days which were almost the same.

For the treatment of PHN using Western medicine combined with KMT, gabapentin was most frequently used alongside acetaminophen, tramadol, and hydrocobalamin. This was the same as the most frequently used medication in the guidelines for the treatment of PHN [1]. In the treatment medication guidelines for PHN, tricyclic antidepressants, anticonvulsants and topical lidocaine are recommended as primary medications, and opioids and tramadol were recommended as secondary medications [45]. Gabapentin is recommended as the primary choice for neuropathy pain because it has no serious complications compared with other anticonvulsants or antidepressants, and it has no interactions with other drugs. It is frequently administered in patients taking multiple medications [46].

Through various studies, moxibustion treatment has been reported to have analgesic effects, neural inhibition or excitatory effects, blood circulation promoting effects, nutritional status enhancement, absorption capacity activation, functional control of various glands, and the ability to increase natural healing [47]. CV12, the most frequently selected point in moxibustion, is the 12^th acupoint of conception vessel meridian and is used for various digestive, neurological, and circulatory conditions/diseases [48]. In the cases in this review, it was used to treat pain, indigestion, and insomnia in PHN patients.

The VAS, the most commonly used method for pain assessment due to PHN, and is easy to apply. It is one of the most widely used methods for objectifying a patient’s subjective pain and is relatively reliable when short-term changes are applied to the patient which can alter the level of pain a patient experiences [49]. However, there is a tendency to only report the intensity of pain [49]. In order to supplement this aspect, Kweon et al [24] evaluated pain using VAS alongside other methods such as PRS, QSP, etc. The symptoms were classified according to the pattern of pain the patients experienced and the degree to which sleep was disturbed due to pain. The NRS is a method where the patient selects a number corresponding to their degree of pain, and is mainly used to assess the overall pain intensity and can be evaluated simply and quickly. Both the VAS and NRS have the advantage of simplicity, however, both have the disadvantage of being a single-dimensional measurement method that measures only the intensity of pain [50]. Therefore, other methods of assessing different aspects of pain in PHN such as intermittent fulminant pain, lancinating pain, and allodynia did not lead to satisfactory results.

This review was conducted to report the current evidence for KMT of PHN. However, the quality of evidence for the treatment with Korean medicine in Korea was insufficient because only case reports existed. In addition to this, the number of research studies was small, and the number of cases in each article was also small (1–2 cases in most of the studies). Moreover, it was difficult to determine the effect of a single treatment because several treatments were often used concurrently.

Nevertheless, this study is significant in that it is a comprehensive analysis of the relatively recent case studies in Korea where KMT is used for PHN. It is also meaningful as this review suggests the possibility that KMT would be effective for PHN symptoms because patients who received KMT improved with no serious side effects. It is believed that well-designed studies that can raise the level of evidence for KMT for PHN and should be conducted in the future. Furthermore, we expect to see KMT in clinical practice guidelines for PHN.

This study analyzed 12 case studies that were selected by searching for clinical research on the topic of PHN published from January 1, 2000, to December 31, 2020 in Korean databases (OASIS, RISS, NDSL, KISS, KMBASE). The following conclusions were reached: