Serologic testing. Serology has limited utility in the diagnosis of acute HZ, but may provide a retrospective diagnosis, if needed. In a study of 260 patients older than 50 years with clinically diagnosed acute HZ, varicella zoster IgA or IgM was positive in 61% of patients at the time of presentation, and in 91% of patients 5 to 10 days later.6
Viral culture. Obtaining a viral culture of varicella zoster is another option, but it is not recommended, as sensitivity is poor and incubation requires several days.
The course of illness, and risk of complications
For some patients, the acute pain and hypersensitivity at the site of the rash resolve in several days; for others, this may take several weeks or more. One recent study found a median of 32.5 days for pain duration in patients ages 50 and older.9 The suffering can last far longer, however, if complications arise.
Postherpetic neuralgia (PHN), a chronic and often debilitating condition with pain that can last months, or even indefinitely, affects about 10% to 15% of patients with HZ.10 Risk factors for the development of PHN include advanced age, female sex, presence of a prodrome, severe acute HZ pain, and a severe rash.11
Trigeminal nerve involvement. HZ affects the first branch of the trigeminal nerve in about 10% to 15% of patients.5 In such cases, the rash may erupt on the forehead, periocular area, and nose. Patients with trigeminal nerve involvement are at significant risk for ocular complications (HZ ophthalmicus), including keratitis, iritis, and possible vision loss, and should be treated and referred to an ophthalmologist without delay.
In addition to these complications, others reported in a review of 859 patients include bacterial skin infection, motor neuropathy, and, rarely, meningitis and HZ oticus.12 Advanced age markedly increased the likelihood of complications.
Initiate treatment without delay
Multiple randomized controlled clinical trials have demonstrated the efficacy of oral antiviral treatment in reducing the duration of viral shedding, accelerating rash healing, and reducing the severity and duration of acute HZ pain.2 In all the studies, however, antiviral therapy was started within 72 hours of the onset of the rash; the efficacy of initiating antiviral treatment after >72 hours has not been systematically studied.2 When it’s not possible to begin therapy within this time frame, however, many experts recommend initiating therapy as soon as possible thereafter.1
Three antiviral agents—acyclovir, famciclovir, and valacyclovir—have been approved by the US Food and Drug Administration to treat HZ. Evidence suggests that famciclovir and valacyclovir have comparable efficacy with regard to resolution of both the rash and the acute pain,13 and result in more rapid pain resolution compared with acyclovir.14,15 Famciclovir and valacyclovir also offer simpler dosing schedules—both are taken 3 times a day, while acyclovir requires 5 daily doses— but they are significantly more expensive (TABLE).
Oral antiviral therapy is strongly recommended for patients who are older than 50 and those who have moderate-to-severe pain or rash—or whose rash appears somewhere other than the trunk.2 But given the safety of oral antiviral agents, treatment can be considered for younger patients and those with milder cases of HZ, as well. (Routine use of antiviral agents is not indicated for unexplained unilateral pain, as varicella zoster infection without the classic rash [zoster sine herpete] is a rare cause.16)
Results regarding the efficacy of oral antiviral agents for reducing the duration of chronic pain and preventing PHN are mixed.2 A recent Cochrane review concluded that oral acyclovir does not significantly reduce the incidence of PHN and that there is insufficient evidence to determine if other antivirals do.17
TABLE
FDA-approved oral antiviral regimens
| Drug | Dosing regimen | Cost of regimen* |
|---|---|---|
| Acyclovir | 800 mg 5 times/d for 7-10 days | $55.97 |
| Famciclovir | 500 mg tid for 7 days | $319.99 |
| Valacyclovir | 1000 mg tid for 7 days | $315.99 |
| *Source: http://www.drugstore.com. Accessed December 6, 2010. | ||
Add a corticosteroid? The evidence is mixed
Oral corticosteroids have been studied as an adjunct to antiviral therapy for the treatment of HZ. One clinical trial of 208 immunocompetent adults older than 50 found that the addition of a 21-day prednisone taper to acyclovir led to accelerated healing of cutaneous lesions, cessation of analgesic use, and return to normal activities and uninterrupted sleep.18 However, this study and another randomized trial of oral corticosteroids did not show that steroids had any effect on longer-term pain relief or the development of PHN.18,19 A recent Cochrane review concluded that there is insufficient evidence that corticosteroids are safe or effective in the prevention of PHN.20 Given the potential adverse effects of oral corticosteroids, their use should be weighed carefully.