Vaccination decreases the overall incidence of virus reactivation but also decreases the severity of disease development and incidence of PHN if reactivation does occur. Secondary prevention
A 2013 Cochrane meta-analysis of 6 randomized controlled trials (RCTs) investigating oral antiviral medications given within 72 hours after the onset of herpes zoster rash in immunocompetent people for preventing postherpetic neuralgia (PHN) found no significant difference between placebo and acyclovir. Additionally, there was no significant difference in preventing the incidence of PHN found in the one RCT included in the meta-analysis that compared placebo to oral famciclovir treatment within 72 hours of HZ rash onset. Studies using valacyclovir treatment were not included in the meta-analysis. PHN was defined as pain at the site of the dermatomic rash at 120 days after the onset of rash, and incidence was evaluated at 1, 4, and 6 months after rash onset. Patients who are prescribed oral antiviral agents after the onset of rash should be informed that their chances of developing PHN are no different than those not taking oral antiviral agents. Treatment
The pain from postherpetic neuralgia can be very severe and requires immediate treatment. There is no treatment which modifies the course of the disease and management primarily aims to control symptoms. Medications
Topical medications
Medications applied to the skin can be used alone if the pain from PHN is mild or in combination with oral medications if the pain is moderate to severe. Topical medications for PHN include low-dose (0.075%) and high-dose (8%) capsaicin and anesthetics such as lidocaine patches.
A 4-fold increase has been used to support the diagnosis of subclinical herpes zoster (zoster sine herpete). However, a rising titer secondary to viral exposure rather than reactivation cannot be ruled out.Imaging studies:
Magnetic resonance imaging lesions attributable to herpes zoster were seen in the brain stem and cervical cord in 56% (9/16) of patients. At three months after onset of herpes zoster, 56% (5/9) of patients with an abnormal magnetic resonance image had developed postherpetic neuralgia. Of the seven patients who had no herpes-zoster-related lesions on the magnetic resonance image, none had residual pain. Prevention
Primary prevention
In 1995, the Food and Drug Administration (FDA) approved the Varicella vaccine to prevent chickenpox. Its effect on postherpetic neuralgia is still unknown. The vaccine—made from a weakened form of the varicella-zoster virus—may keep chickenpox from occurring in nonimmune children and adults, or at least lessen the risk of the varicella zoster virus lying dormant in the body and reactivating later as shingles. If shingles could be prevented, postherpetic neuralgia could be completely avoided.In May 2006 the Advisory Committee on Immunization Practices approved a new vaccine by Merck (Zostavax) against shingles. This vaccine is a more potent version of the chickenpox vaccine, and evidence shows that it reduces the incidence of postherpetic neuralgia. The CDC recommends use of this vaccine in all persons over 60 years old.The most effective means of preventing PHN from a herpes zoster infection is prior vaccination with the varicella vaccine.