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Shingles: diagnosis and treatment

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VOL: 96, ISSUE: 50, PAGE NO: 36

Fiona Scott, RGN, RHV, is research sister, virology department, Barts and The London NHS Trust

Shingles (Herpes zoster) is caused by a reactivation of the chickenpox (varicella) virus which lies dormant on the dorsal root ganglia after the primary infection. Also known as varicella zoster virus (VZV), the disease can vary in intensity from a mildly painful irritation to a severe and disfiguring illness that needs long-term medication. The virus travels down the sensory nerve, typically producing painful vesicles on the area of skin the nerve supplies (the dermatome).

Often two to three adjoining dermatomes are involved, with the thoracic and trigeminal nerves being the most common (see Box 1 for symptoms). The term ‘zoster associated pain’ (ZAP) is used to describe these symptoms in the acute and chronic stages of the illness. The vesicles are full of the virus, which can sometimes be detected in the blood.

Shingles also causes a persistent and debilitating condition known as postherpetic neuralgia (PHN). This is pain that persists for one month or longer after the acute illness.

Epidemiology

Shingles is not a notifiable disease so there is no accurate data on its incidence, but estimates calculated from studies based on small populations put the figure at 120,000 cases a year in the UK (Johnson, 1995; Wood et al, 1995). Unlike chickenpox it is not seasonal.

People with shingles can transmit the varicella virus to anyone who is immunocompromised or has not had chickenpox. This means they can pass chickenpox on but not shingles.

The shingles study

This ongoing study was set up with the following objectives:

- To help define the underlying reasons for the variation in the pattern and intensity of shingles, such as strain of virus, demographic and ethnic factors and immune status;

- To assess the accuracy of shingles diagnoses;

- To assess the usefulness of laboratory tests in confirming a diagnosis;

- To identify which features of clinical presentation confirm a diagnosis;

- To identify interventions to prevent PHN.

Diagnosing shingles

Diagnosis is usually based on a clinical examination but our study is evaluating the effectiveness of the following tests in diagnosing cases that are not clear:

- The culture of vesicle fluid;

- Electron microscopy and immunofluorescence of vesicle fluid;

- The detection of viral DNA in vesicle fluid using the technique of polymerase chain reaction (PCR);

- The detection of viral DNA in blood using PCR, a new test being developed in our department that may help to predict those at risk of long-term pain.

We have defined a ‘confirmed diagnosis of shingles’ as confirmation by one of the above tests or a clear dermatomal vesicular rash accompanied by prodromal pain.

After shingles has been diagnosed, patients who continue to have pain or abnormal sensations are followed up at six weeks, three months, six months and one year. We use a visual analogue scale and the McGill pain questionnaire (Melzack, 1975) to assess pain and collect further blood samples. This data has yet to be analysed. Patients whose pain is difficult to control are referred to a pain consultant.

We have had the cooperation of GPs in four health authorities in east London and take referrals of acute cases of shingles directly from GPs and staff at Barts and the London NHS Trust. We have enrolled 215 patients for the study. Of these, 185 (86%) were correctly diagnosed with shingles by the referrer, but our figures indicate that 8.8% were treated unnecessarily with antivirals. This suggests that fast, accurate diagnostic testing could reduce unnecessary prescribing.

The normal incidence of VZV is three in 1,000 a year (Johnson, 1995), with the risk increasing with age. However, our data shows an unexpectedly high number of cases in the 30-35 age group (Box 2). We have no explanation for this.

The treatment of acute shingles

We used the following guidelines to determine when to recommend a systemic antiviral treatment:

- All ophthalmic zoster (where the eye area is involved);

- All immunosuppressed patients;

- All patients aged over 55;

- All patients with disseminated zoster.

Systemic drugs are most beneficial if they are started within 72 hours of the onset of the rash (Beutner et al, 1995). Aciclovir 800mg taken five times a day is the most commonly used systemic treatment and 69.5% of our patients with a confirmed diagnosis were treated with antivirals.

Skin care

Topical antivirals are available but are useful only in combination with systemic antivirals for ophthalmic zoster. Some patients found calamine lotion helped to relieve burning pain and itching during the acute phase. Otherwise the lesions should be left to dry and form a scab naturally. Non-adherent dressing should be used only if the lesions are weeping, raw or sticking to bedding and clothing. Such symptoms often indicate a secondary bacterial infection.

Analgesia

Dihydrocodeine, codeine and paracetamol combinations, and paracetamol with the addition of low-dose amitriptyline (10-75mg at night) were our recommended analgesics. Tricyclic antidepressants such as amitriptyline have been shown to reduce the intensity of pain in 60-70% of patients with ZAP (Johnson, 1995). The dosage was adjusted according to each patient’s pain levels and tolerance of the drugs.

Treatment of postherpetic neuralgia

PHN is usually treated with a combination of the analgesic drugs mentioned. Up to 14% of patients with shingles develop PHN (Wood, 1991) and as many as 30% of these still have pain after a year, so it is important that different treatment regimes are available if necessary. Gabapentin has recently been licensed for the treatment of neuropathic pain and is useful for patients who have not responded to more conventional analgesia.

Many patients ask if there is anything they can ‘rub in’ to get rid of the tingling, itching and discomfort of allodynia. Topical capsaicin (Watson et al, 1993) has been effective in US trials, but as it burns when applied few patients are able to persist with its use.

Of the 108 patients who have completed our study, 14.8% still have pain or abnormal sensations after one year. They have tried different combinations of analgesia during their year on the trial with limited success. Of these patients, 37.5% still have pain that requires regular analgesia which does not control the pain, 12.5% control the pain with analgesia and the rest have found nothing effective and have therefore stopped all medication.

Starting systemic antivirals within 72 hours of the onset of the shingles rash has been shown to reduce the percentage of people who develop PHN (Beutner et al, 1995). We are in the process of using our data to draw up guidelines to assist with accurate diagnosis without using laboratory tests.

Conclusions

When dealing with shingles, prompt diagnosis is necessary for antiviral treatment to be effective - a patient questionnaire for the use of GPs that emphasises a unilateral rash, prodromal pain and allodynia would be a useful diagnostic tool. Predicting those who are likely to develop PHN at diagnosis could help to prevent long-term debility.

We found the presence of VZV DNA in baseline blood to be strongly associated with the development of PHN. The prodrug of aciclovir, valciclovir, has been shown to reach therapeutic levels in the blood 34% faster than aciclovir (Beutner et al, 1995). A fast, accurate blood test would help to target those most at risk of developing PHN so that they could receive more effective antiviral therapy.

These patients could also be targeted for earlier treatment with amitriptyline, gabapentin and carbamazepine, allowing further research into their efficacy in preventing the development of PHN.

Our data on pain and its impact on mental state and quality of life has yet to be analysed. At present the small number of patients suffering from long-term PHN would make the results of any analysis statistically insignificant. However, the long-term effects of pain and allodynia, which contribute to depression, have been well documented.

Acute shingles and the management of PHN is an ideal area for the development of a nurse-led service linking the acute and community settings. Such a service would help to promote research into an intractable area of pain management.

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