What is Postherpetic Neuralgia?
Postherpetic neuralgia (PHN) is a chronic neuropathic pain condition that persists for 3 months or more following the healing of a herpes zoster (shingles) rash, resulting from reactivation of the dormant varicella zoster virus in dorsal root ganglia. 1, 2, 3
Pathophysiology and Mechanism
PHN represents a distinct disease entity separate from acute herpes zoster, involving aberrant somatosensory processing in both peripheral and central nervous systems. 4 The condition is characterized by:
- Inflammatory necrosis of dorsal root ganglia with associated neuritis, leptomeningitis, and segmental unilateral degeneration of related motor and sensory roots 5
- Peripheral nerve fiber damage with secondary central brain changes, resulting in altered sensory and nerve function including upregulation of nociception at every level of the nervous system 1
- Denervation pain where deprivation of coherent sensory information produces pain that conveys incorrect messages, rather than pain from overstimulation 1
Clinical Presentation
Patients with PHN typically experience multiple distinct pain types:
- Continuous burning, tingling, itchy, or tender sensations that persist in the dermatomal distribution where the original shingles rash occurred 1
- Paroxysmal lancinating pain that can be sharp and shooting in character 5, 3
- Allodynia where typically non-painful stimuli (such as light touch or clothing contact) trigger severe pain 3
- Hyperalgesia where painful stimuli produce exaggerated pain responses beyond what would be expected 3
Epidemiology and Risk Factors
The most significant risk factor for developing PHN is advanced age, with at least 50% of shingles patients over age 65 developing PHN. 2, 5 Additional risk factors include:
- Severity of pain during acute shingles correlates with higher PHN risk 2
- Trigeminal nerve distribution of the original herpes zoster infection 2
- Immunocompromised states, particularly advanced HIV disease where PHN can be incapacitating 1, 6
- Psychological distress and stressful life events appear to play a role in both shingles onset and PHN development 7
Natural History and Prognosis
- PHN accounts for 11-15% of all pain clinic referrals, representing a significant burden on healthcare systems 2
- Pain may persist for months to years in affected patients, with some requiring long-term treatment 8, 7
- The condition often leads to depression, disrupted sleep, decreased functioning, and increased healthcare utilization due to its chronic and refractory nature 7
- The rash itself evolves through stages of vesicles, pustules, and crusts, with new vesicle formation continuing for 3-5 days and crusts typically persisting for 2-3 weeks before resolving 6
Common Pitfalls
A critical caveat is that PHN is frequently unresponsive to treatment modalities, with response to therapy being generally inhomogeneous across patients. 4 Some patients achieve long-term pain control with monotherapy, while others—particularly those with central nervous system lesions—remain extraordinarily refractory to all measures. 4