Definition and Overview
Postherpetic neuralgia (PHN) is the most common complication of herpes zoster (shingles), defined as pain persisting in the affected dermatome for more than 3 months after the rash has healed. It develops in 10-20% of herpes zoster patients and up to 50% of those over age 60 [1].
Pathophysiology
Varicella-zoster virus reactivation from dorsal root ganglia causes nerve damage including dorsal root ganglion inflammation, peripheral nerve demyelination and axonal degeneration, dorsal horn sensitization, and reorganization of central pain processing [2].
The combination of peripheral nerve damage (deafferentation) and central sensitization produces the characteristic pain phenotype.
Risk Factors
- Age >50 (strongest risk factor): incidence increases sharply with age
- Severe acute pain during herpes zoster
- Severe rash (extensive dermatomal involvement)
- Immunosuppression
- Ophthalmic division (V1) involvement
- Female sex
Symptoms
Pain is described as burning, stabbing, or deep aching in the affected dermatome [3]. Allodynia (pain from light clothing contact or gentle touch) is present in many patients. Paroxysmal shooting or electric shock-like pain may be superimposed on constant pain. The thoracic dermatomes are most commonly affected.
Treatment
Pharmacotherapy
First-line [4]:
- Gabapentin (1200-3600 mg/day) or pregabalin (150-600 mg/day)
- Tricyclic antidepressants: nortriptyline or amitriptyline (25-150 mg/day)
- Topical lidocaine 5% patch (up to 3 patches for 12 hours/day)
- Capsaicin 8% patch (single application, repeat every 3 months)
Second-line: tramadol, duloxetine. Third-line: strong opioids (with caution). Combination therapy is often necessary.
Interventional
Intercostal or paravertebral nerve blocks, epidural steroid injections, and intrathecal methylprednisolone for refractory cases. Spinal cord stimulation for severe, treatment-resistant PHN.
Prevention
The recombinant zoster vaccine (Shingrix) reduces herpes zoster risk by 97% in adults aged 50+ and is the most effective prevention strategy [5]. Two doses given 2-6 months apart. Recommended for all adults aged 50 and older, regardless of previous herpes zoster or varicella vaccination history.
Early antiviral treatment (valacyclovir, famciclovir) within 72 hours of rash onset reduces PHN risk. Aggressive acute pain management during herpes zoster may also reduce PHN incidence.