Postherpetic neuralgia

Background

Sensory dermatomes by spinal level.

• Postherpetic neuralgia (PHN) is a complication of acute herpes zoster (AHZ), also known as "Shingles"
• While AHZ is usually painful, PHN refers to pain which becomes severe and persists after the vesicular lesions of AHZ are no longer forming. There is an overlap between acute zoster pain and PHN pain, and together they are sometimes referred to as Zoster Associated Pain. However, if pain persists beyond 3 months from time of vesicle formation it is termed PHN.
• PHN can be challenging to treat, and may require trials and titration of various therapies, usually in a primary care or neurology outpatient setting.
• Prevention of PHN by early antiviral therapy for AHZ is a cornerstone of ED management
• Prevention of shingles via childhood varicella vaccination and adult shingles vaccination, in a primary care setting is the single most important preventing step

Clinical Features

• Pain in the same unilateral dermatomal distribution of a recent shingles episode which becomes more severe after the vesicular phase of shingles
• Lancinating or burning pain which persists beyond 3 months after the shingles episode
• Scars may be evident from recent shingles
• Hypersensitivity, hypoesthesia, hyperalgesia or allodynia in the area.
• Autonomic dysfunction in the area (e.g. excessive sweating)

Differential Diagnosis

• Acute zoster pain (see Shingles)
• Other neuralgias and neuropathies (trigeminal, diabetic)
• Other causes of chest wall pain (e.g., rib injury)
• Pleuritic chest pain (pulmonary embolism, pneumothorax,pneumonia)

Evaluation

Workup

• Typically, none
  • If other differentials are considered, workup would be tailored to confirming or ruling out those processes

Diagnosis

• Typically a clinical diagnosis based on recent acute zoster plus ongoing symptoms.

Prevention

Treating shingles with antiviral therapy within 72 hours of rash appearance plays an important role in preventing the development of PHN. For immunocompromised patients, antiviral therapy should be initiated even after 72 hours. Routine vaccination for varicella in childhood, and for shingles prevention in adulthood is the best prevention for shingles and PHN

Management

Given that the pain is often difficult to control, much of the management will occur in a primary care setting, and will often involve trials and titration of multiple agents.

ED setting

• Gabapentinoid, either Pregabalin or Gabapentin
• Lidocaine 5% patch
• For short term relief of acute pain exacerbation:
  • Ketamine infusion
  • IV lidocaine infusion

Primary Care Setting

• Tricyclic antidepressants (TCA)
• Topical capsaicin

Invasive

• Sympathetic blockage
• Spinal stimulators

Disposition

• Usually discharge home with pain management as described above.

See Also

• Shingles

References

• J. Tang, Y. Zhang, C. Liu, A. Zeng, and L. Song, “Therapeutic Strategies for Postherpetic Neuralgia: Mechanisms, Treatments, and Perspectives,” Curr Pain Headache Rep, vol. 27, no. 9, pp. 307–319, Sep. 2023, doi: 10.1007/s11916-023-01146-x.
• E. Y. Gan, E. A. L. Tian, and H. L. Tey, “Management of herpes zoster and post-herpetic neuralgia,” Am J Clin Dermatol, vol. 14, no. 2, pp. 77–85, Apr. 2013, doi: 10.1007/s40257-013-0011-2.
• C. Gruver and K. B. Guthmiller, “Postherpetic Neuralgia,” in StatPearls, Treasure Island (FL): StatPearls Publishing, 2024. Accessed: May 08, 2024. [Online]. Available: http://www.ncbi.nlm.nih.gov/books/NBK493198/
• “Herpes Zoster Treatment & Management: Approach Considerations, Topical Treatments, Pharmacologic Therapy for Herpes Zoster,” Jun. 2023, Accessed: May 08, 2024. [Online]. Available: https://emedicine.medscape.com/article/1132465-treatment