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Treatment of postherpetic neuralgia
Clinical bottom line: Tricyclic antidepressants are effective in relieving
postherpetic neuralgia (odds ratio 0.15 (0.08 to 0.27)). Topical capsaicin
is also associated with effective pain relief at the recommended dose
(odds ratio 0.29 (0.16 to 0.54)).
There is currently insufficient evidence to determine whether transcutaneous
nerve stimulation (TENS), benzodiazapines, antiviral agents, anti-prostaglandins
and acupuncture are effective. Current evidence suggests that they are
not, and these treatments should not be used. Weak evidence suggests
that vincristine iontophoresis may have some benefit, but side effects
are unpleasant. More proven treatments are therefore recommended.
This has been defined as pain persisting in the dermatomes affected
by herpes zoster (shingles) after the disappearance of the rash caused
by the infection.
Up to 15% of untreated patients have persistent pain one month after
healing of an acute herpetic rash. One quarter of these (4% of total)
still have pain at one year. The risk of postherpetic neuralgia increases
sharply with age, and can be as high as 50% in patients aged over 60
years and 75% in those aged over 75 years.
Treatment during the acute phase has been covered in a separate review
(Lancaster et al, 1995). This review considers treatment during the
chronic phase of the condition.
Systematic review
Volmink J, Lancaster T, Gray S, Silagy C. Treatments for postherpetic
neuralgia: A systematic review of randomized controlled trials. Family
Practice. 1996; 13: 84-91. ISSN: 0263-2136.
Date review completed: December 1993
Number of trials included: 12
Main outcomes: pain relief after treatment.
Inclusion criteria were randomised controlled trials of postherpetic
neuralgia, where pain had persisted for at least one month after onset
of herpes zoster; at least two treatment groups.
Pain data were extracted. Expected event rates were subtracted from
observed event rates for each trial. Estimate of effect size was calculated
using odds ratios with 95% confidence intervals.
Findings
Tricyclic antidepressants
Five trials were included. Three trials compared a tricyclic (amitriptyline
or desipramine) with placebo. Three of three trials demonstrated better
pain relief with a tricyclic. The odds ratio was 0.15 (0.08 to 0.27).
However, desimpramine was associated with some potentially serious side
effects. One trial also examined maprotiline, and found no benefit over
amitriptyline.
Transcutaneous electrical nerve stimulation
One low quality trial compared combination clomipramine and carbamazepine
with transcutaneous electrical nerve stimulation (TENS). Combination
therapy was better than TENS, with an odds ratio of 0.15 (0.03 to 0.7).
Benzodiazapines
One trial compared lorazepam with placebo and amitriptyline. Lorazepam
was not associated with any benefit: odds ratio 1.00 (0.24 to 4.18).
It was associated with sedation and low mood, including onset of severe
depression in some patients.
Antiviral
One small trial demonstrated no benefit of acylovir treatment compared
with placebo; odds ratio 1.16 (0.21 to 6.47). However, group size may
be too small to demonstrate an effect.
Topical capsaicin
Three placebo-controlled trials were included. Two of three trials demonstrated
significant benefit of capsaicin (0.075% for six weeks) over placebo.
The remaining trial was large, but used a weaker preparation (0.025%
for four weeks). Capsaicin was associated with skin reactions which
lessened during treatment.
Anti-prostaglandin
One trial compared benzydamine with placebo. There was no significant
benefit, with an odds ratio of 1.2 (0.37 to 3.92). Rashes were more
frequent in benzydamine patients.
Iontophoresis
One small trial of transdermal vincristine iontophoresis showed significant
benefit over saline-only placebo: odds ratio 0.05 (0.01 to 0.26). However
skin irritation and painless burns were common in both groups.
Acupuncture
One trial showed no benefit of acupuncture over placebo (mock TENS):
odds ratio 0.92 (0.28 to 3.00). Failure to complete treatment was high
because of the pain associated with acupuncture.
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