Postherpetic neuralgia

Disease Description (Causes and Symptoms)

• Definition: Postzoster neuralgia (PHN) is chronic neuropathic pain that persists in the affected area even after a certain period (some definitions use 1 month, while other criteria use 3 months) has passed since the skin rash of herpes zoster developed.

• Causes/pathophysiology: Varicella-zoster virus, which causes chickenpox in childhood, remains latent in the nerve ganglia and reactivates when immunity is reduced, causing inflammation in the nerves and skin. As nerve damage and inflammation in the acute phase persist, sensitization of the peripheral and central nervous systems (central/peripheral sensitization), desensitization, or axonal degeneration may occur, leading to chronic pain.

• Main symptoms:

  • Severe, band-like pain localized to one side (burning, stabbing, throbbing, etc.)
  • Skin lesions (blisters) heal within 2–3 weeks, but the pain persists
  • Reduced sensation or abnormal sensation in the painful area (extreme pain from the touch of clothing; allodynia)
  • Sleep disturbances, depression·anxiety, and limitations in daily activities

• Risk factors: Older age (especially 60 years or older), immunosuppression, chronic diseases such as diabetes, and female sex.

Treatment Methods (Standard Treatment · Medications · Procedures · Lifestyle Management · Precautions)

• Treatment goals: Pain relief, recovery of function (sleep·daily activities), and prevention of complications rather than complete cure.

• Treatment during the acute phase (early in the development of herpes zoster) (preventive importance)

  • Antiviral medications: Administer as soon as possible after the rash begins (generally within 72 hours).
    • Examples: acyclovir, valacyclovir, and famciclovir. (Follow the physician’s instructions regarding the duration and dosage.)
  • Topical treatment of skin lesions and pain management (analgesics, nerve blocks if necessary, etc.)
  • Early, active treatment lowers the risk and severity of PHN.

• Pharmacological treatment of chronic PHN (first-line options)

  • Anticonvulsants (first-line choices for neuropathic pain): gabapentin, pregabalin
  • Tricyclic antidepressants (TCAs): amitriptyline, nortriptyline
  • Topical treatment: lidocaine patch (5%), high-concentration capsaicin patch (8%) — administered by a specialist
  • Other: When there is no response to medication, a weak opioid (e.g., tramadol) may be considered (beware of side effects·addiction potential)

• Procedural and nonpharmacological treatments

  • Nerve blocks (e.g., epidural injections, sympathetic nerve blocks), continuous nerve blocks, transcutaneous electrical nerve stimulation (TENS), percutaneous nerve stimulation or spinal cord stimulation, etc.
  • Pulsed radiofrequency, local cryotherapy, and injection of local anesthetics may be used to relieve symptoms in some patients.
  • Mental health·sleep improvement, physical therapy, and pain rehabilitation programs are recommended.

• Precautions / Side effects

  • Anticonvulsants: Dizziness, drowsiness, edema, weight gain, etc.
  • TCAs: Anticholinergic side effects (dry mouth, constipation, orthostatic hypotension), effects on the electrocardiogram (caution in older adults)
  • Opioids: Constipation, drowsiness, risk of dependence
  • Lidocaine and capsaicin patches may cause local irritation
  • In immunocompromised patients and older adults, susceptibility and potential drug interactions should be carefully evaluated when selecting treatment

Checklist Before an Outpatient Visit (Items to Prepare and Information to Provide to Medical Staff)

• Items to prepare/bring:

  • A list of all medications currently being taken (including prescription drugs·OTC medications·supplements)
  • Previous medical certificates·hospital records (date herpes zoster began, medical certificate, previous test results)
  • The date the rash began and the date the pain began (write the dates if possible)
  • The pattern·severity of the pain (pain diary: when it is worse during the day, triggering factors, relieving factors)
  • Previous treatment (whether antiviral medication was administered, duration of use, response to pain medications)
  • Underlying diseases (diabetes, cancer·immunosuppressive treatment, heart disease, etc.) and allergy information
  • Whether you have received the herpes zoster vaccine

• Examples of items medical staff mainly check during an outpatient visit:

  • Duration of pain (time elapsed since the rash), distribution of pain (dermatome), and presence of abnormal sensation
  • When previous antiviral treatment was started and the response
  • Effects on sleep·mental status (whether depression·anxiety is present)
  • Presence of medication side effects and the possibility of drug interactions

Examples of General Questions to Ask the Doctor

• "What side effects can I expect from this medication (e.g., gabapentin/amitriptyline), and how might they affect my daily life?"
• "What is the prognosis for my pain? When can I expect improvement?"
• "Can herpes zoster be prevented from recurring? Would vaccination help?"
• "If medication is ineffective, what are the indications and risks of procedural treatments (nerve blocks, electrical stimulation, etc.)?"

Examples of Disease-Specific Questions

• "Does my risk of PHN differ depending on when I started antiviral treatment, which medication I took, and how long I took it when I developed herpes zoster? Would antiviral medication help even now?"
• "For my current pain, which approach is recommended first among gabapentin, a lidocaine patch, and a capsaicin patch? What are the expected effects and side effects of each method?"

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Note: Diagnosis and treatment vary depending on the individual’s condition (age, comorbidities, medication allergies, etc.). The information above is general guidance; please consult your healthcare provider regarding the final prescription and treatment plan.