Post-Herpetic Neuralgia (PHN)
The condition is called post-herpetic neuralgia (PHN), defined as nerve pain persisting 3 months or more after the herpes zoster rash has healed. 1, 2
Definition and Clinical Characteristics
PHN is formally defined as pain that persists 1 to 3 months following resolution of the herpes zoster rash, with most guidelines using the 3-month threshold as the standard diagnostic criterion. 3, 2
The condition results from nerve damage caused by varicella zoster virus reactivation, which travels along nerve pathways causing inflammation and permanent damage to peripheral nerves and dorsal root ganglia. 4
Patients typically describe two distinct pain patterns: a constant deep, aching, or "cold burning pain" in the affected dermatome, and intermittent lancinating (shooting) pain that is often triggered by light touch. 1, 2
Allodynia (pain from normally non-painful stimuli like clothing touching the skin) and hyperalgesia (exaggerated pain response to painful stimuli) are hallmark features that significantly impair quality of life. 2, 5
Epidemiology and Risk Factors
Age is the single most important risk factor: approximately 50% of herpes zoster patients over age 60 develop PHN, compared to only 15% of all herpes zoster patients overall. 3, 6
PHN can be particularly incapacitating in immunocompromised patients, including those with advanced HIV disease, who face higher rates of both herpes zoster and subsequent PHN. 1, 4
Treatment Approach
First-Line Pharmacological Options
Tricyclic antidepressants (TCAs) such as amitriptyline, nortriptyline, and doxepin are the most comprehensively studied first-line agents, demonstrating efficacy in approximately 50% of PHN patients. 1, 4, 7
However, TCAs are frequently contraindicated or poorly tolerated in elderly patients (the primary PHN population) due to anticholinergic side effects, orthostatic hypotension, and cardiac conduction abnormalities. 7, 6
Gabapentin represents an equally effective first-line alternative with superior tolerability, particularly in elderly patients, based on multiple randomized controlled trials demonstrating significant pain reduction, improved sleep, mood, and quality of life. 8, 7, 6
Pregabalin (an alpha-2 delta ligand like gabapentin) has proven efficacy in multiple double-blind trials, with studies showing statistically significant improvement in pain scores and increased proportions of patients achieving ≥50% pain reduction from baseline. 9, 2
Dosing Considerations
For gabapentin, effective doses range from 1800-3600 mg/day divided three times daily, with titration starting at 900 mg/day over 3 days, then increasing by 600-1200 mg/day increments every 3-7 days to target dose. 8
For pregabalin, effective doses are 150-300 mg twice daily or 100-200 mg three times daily, with dose adjustments required for patients with creatinine clearance 30-60 mL/min. 9
Alternative and Adjunctive Therapies
Topical lidocaine 5% patches and capsaicin cream provide localized pain relief and can be used as monotherapy for mild cases or as adjuncts to systemic medications. 2, 5
Opioid analgesics (including tramadol) may be necessary for adequate pain control in refractory cases, though they should be reserved for patients who fail first-line therapies. 2, 5
Carbamazepine has demonstrated efficacy but is generally reserved for cases with prominent lancinating pain components. 2
Critical Clinical Pitfalls
The most effective strategy is prevention through vaccination, not treatment after PHN develops—the recombinant zoster vaccine (Shingrix) demonstrates 88.8% efficacy against PHN development. 4
Starting antiviral therapy (acyclovir, famciclovir, or valacyclovir) within 72 hours of rash onset may reduce PHN incidence by up to 60%, though evidence for long-term PHN prevention remains limited. 3, 5
Monotherapy frequently fails in PHN—be prepared to use mechanism-based combination therapy (e.g., TCA or gabapentin plus topical agent) when single agents provide inadequate relief. 7, 2
Response to therapy is inherently inhomogeneous; some patients achieve long-term control with monotherapy while others with central nervous system involvement remain extraordinarily refractory to all measures. 7