EVIDENCE-BASED ANSWER
Postherpetic neuralgia occurs rarely among patients aged <50 years with herpes zoster. The incidence, duration, and severity of post-herpetic neuralgia increases with age, but older patients usually have only mild pain. Most cases resolve spontaneously within 3 months.1,2
Even in the highest-risk group, people aged >70 years, 25% had some pain at 3 months, but only 10% had pain at 1 year, and none had severe pain. Only a few patients have pain that persists for years (strength of recommendation: A, based on a well-done prospective cohort study).
Evidence summary
Postherpetic neuralgia is defined as pain that persists more than 1 month following onset of herpes zoster. The annual incidence of herpes zoster in population-based studies ranges from 1/1000 to 2/1000.1,3 Among adults aged >60 years, the annual incidence increases to 3.6/1000 for men and 5.6/1000 for women.1
In a prospective study performed in a primary care setting in Iceland, all cases of herpes zoster and postherpetic neuralgia occurring over 4.5 years in a population of 100,000 were identified, and all cases of postherpetic neuralgia were followed for up to 7.6 years. Few patients (4%) received antiviral medication.
In this study, postherpetic neuralgia followed herpes zoster in 2% of patients under age 40, 21% between the ages of 40 and 60, and in 40% of those over age 60.1,2 Subjects self-described pain as none, mild, moderate, or severe. Patients aged >60 years had the worst prognosis: 18% still had mild pain at 3 months and 6% had moderate or severe pain. At 1 year, 8% had mild pain and 2% had moderate pain. No patients had severe pain after 12 months.1,2
Among the 14 patients with pain persisting >12 months, 7 had complete resolution of pain, 5 had persisting pain that either improved or remained mild, 1 had ongoing moderate pain at 7 years, and 1 was lost to follow-up.2 (See Table.) Although postherpetic neuralgia can recur after resolution,4 no recurrence of pain was found among 183 randomly selected patients who had had resolution by 1 year.2
These results are similar to those found in an analysis of a retrospective cohort drawn from a large general practice network database,5 as well as other population-based studies.6,7 The prognosis is better than that reported in the placebo arms of trials of acute herpes zoster treatment.4 Patients in such trials are more likely to have severe disease than those seen in primary care settings.
TABLE
Risk of postherpetic neuralgia by age
| Age (y) | Pain at 3 mo | Pain at 1 y |
|---|---|---|
| >50 | 3% mild | 0% |
| 50–59 | 4% mild | 4% mild |
| 60–69 | 9% mild | 3% mild |
| 4% moderate to severe | 1% moderate | |
| ≥70 | 18% mild | 8% mild |
| 6% moderate to severe | 2% moderate |
Recommendations from others
A British guideline states that 5% of herpes zoster patients have postherpetic neuralgia 1 year after shingles.8 A review in the New England Journal of Medicine states that 48% of herpes zoster patients aged >70 years have postherpetic neuralgia at 1 year.9 This prevalence comes from a retrospective cohort study that combined patients presenting to a referral center with herpes zoster or postherpetic neuralgia into a single cohort, thus overestimating the prevalence of postherpetic neuralgia and providing a less reliable prognosis.10
CLINICAL COMMENTARY
Larry Halverson, MD
Cox Health Systems Family Practice Residency Program, Springfield, Missouri
Knowing the overall good prognosis for postherpetic neuralgia is helpful as I encounter patients with shingles. This answer is consistent with my experience. Fear of potential interminable pain and anecdotal experience with prolonged patient suffering has seduced me to start medications to “prevent” this problem. In some cases, my unnecessary (and unproven) “preventive” medications have produced new problems. Future research should focus on effective pain treatment options instead of prevention of a condition that usually resolves with time.