Definition and Overview
Postherpetic neuralgia (PHN) is chronic neuropathic pain that persists for more than 3 months after the herpes zoster rash caused by the varicella-zoster virus (VZV) disappears. It is the most common and difficult to treat among complications of shingles, and has a serious impact on quality of life.
Postherpetic neuralgia occurs in approximately 10-15% of shingles patients over the age of 50, and the incidence increases to over 20% in people over the age of 70. Clinical importance is increasing in an aging society.
pathophysiology
acute nerve injury
VZV remains latent in the dorsal root ganglion or trigeminal ganglion after previous chickenpox infection. In immunocompromised conditions, the virus can be reactivated, causing inflammation and necrosis in ganglia and nerve fibers.
Chronic pain formation mechanism
After acute ganglion damage, chronic neuropathic pain persists through the following mechanisms:
- Peripheral sensitization: abnormal firing of damaged nerve fibers, overexpression of sodium channels
- Central sensitization: Modification of pain processing circuitry in the dorsal horn of the spinal cord, activation of NMDA receptors
- Loss of inhibitory nerves: Decreased pain control function due to damage to inhibitory interneurons.
- Allodynia occurs: Aβ fibers (non-pain tactile fibers) are incorporated into the pain pathway.
risk factors
Factors that increase the risk of developing postherpetic neuralgia are as follows.
- Old age (strongest risk factor): Incidence rate increases sharply in people over 70 years of age.
- Acute Pain Severity: Severe acute pain increases the risk of chronic pain.
- Rash Extent: Widespread skin rash
- Trigeminal nerve branch involvement: facial herpes zoster
- Immunocompromised: HIV infection, chemotherapy, use of immunosuppressants
- Diabetes and other chronic diseases
symptoms
The pain of postherpetic neuralgia shows typical characteristics of neuropathic pain.
pain type
- Burning pain: persistent pain that feels like the skin is burning
- Shooting/stabbing pain: Paroxysmal pain that feels like an electric shock or knife stabbing.
- Allodynia: Severe pain caused by light touch, friction of collar, or wind.
- Hyperalgesia: Excessive response to painful stimuli.
accompanying symptoms
- Numbness or tingling
- sleep disorder
- depression, anxiety
- social activity restrictions
Occurrence site
Thoracic dermatomes are the most common (about 50%), followed by the face (first branch of the trigeminal nerve, herpes zoster) and the neck.
diagnosis
The diagnosis of postherpetic neuralgia is made clinically.
Diagnostic criteria
- Pain that persists for more than 3 months after the shingles rash disappears
- Distribution of dermatomes consistent with the site of previous shingles outbreaks
- Neuropathic pain characteristics (burning, allodynia, stabbing pain)
Pain assessment
- Visual Pain Scale (VAS), Numeric Pain Scale (NRS)
- Neuropathic Pain Questionnaire (DN4, LANSS)
- Quality of Life Assessment (SF-36)
Differential diagnosis
- recurrent shingles
- Trigeminal neuralgia (when trigeminal nerve branches are involved)
- Other neuropathic pain
treatment
Primary drug treatment
Gabapentinoids Gabapentin and pregabalin inhibit abnormal neuronal firing by blocking voltage-dependent calcium channels. In a systematic literature review, the effect of reducing pain intensity by more than 50% was confirmed.
Tricyclic antidepressants A representative example is amitriptyline, which is effective in controlling pain and improving sleep. Caution is required in the elderly due to cardiovascular side effects and anticholinergic effects.
topical treatment - Lidocaine patch (5%): Particularly effective for allodynia, with few systemic side effects. - High-concentration capsaicin patch (capsaicin 8%): Induces skin TRPV1 receptor desensitization, performed at medical institutions
Secondary and adjuvant treatment
- Opioids: Limited use for severe pain unresponsive to other treatments.
- SNRI (duloxetine): For neuropathic pain and depression
- Nerve block: epidural steroid injection, stellate ganglion block
Non-pharmacological treatment
- Transcranial Magnetic Stimulation (TMS): Actions on central pain control circuits
- Transcranial Direct Current Stimulation (tDCS): Pain Control in Research Phase
- Cognitive Behavioral Therapy: Managing Psychosocial Aspects of Chronic Pain
prevention
shingles vaccine
The recombinant shingles subunit vaccine (Shingrix, RZV) showed a 97% effectiveness in preventing shingles and a 91.2% effectiveness in preventing postherpetic neuralgia in people over 50 years of age. It has superior effectiveness and durability compared to the existing live vaccine (Zostavax).
Active treatment in acute phase
Administering antiviral drugs (acyclovir, valacyclovir) within 72 hours after the onset of shingles can reduce nerve damage and lower the risk of developing postherpetic neuralgia.
Complications and Prognosis
Untreated or unresponsive to treatment, postherpetic neuralgia can lead to problems such as:
- Sleep Disorders and Chronic Fatigue
- Depression and anxiety disorders
- Social isolation, poor occupational functioning
- Increased risk of falls (elderly patients)
The intensity and duration of pain varies greatly from person to person, and although spontaneous improvement occurs in many patients within a year after onset, in some cases it persists for several years. Early active treatment and a multidisciplinary approach are important to improve prognosis.
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This information is provided for medical educational purposes and is not a substitute for individual medical care or treatment. If you have any symptoms, be sure to seek professional advice. Inquiries: Osang Neurosurgery 1599-5453 | osns.co.kr