What is herpes zoster?
Herpes zoster is a localised, blistering and painful rash caused by reactivation of varicella zoster virus (VZV). It is characterised by dermatomal distribution, ie the blisters are confined to the cutaneous distribution of one or two adjacent sensory nerves.
Herpes zoster is also called shingles.
VZV is also called herpesvirus 3, and is a member of the Herpesvirales order of double-stranded DNA viruses.
Who gets herpes zoster?
Anyone that has previously had varicella (chickenpox) may subsequently develop zoster. This can occur in childhood but is much more common in adults, especially the elderly. People who have had zoster rarely get it again; the risk of getting a second episode is about 1%.
Herpes zoster often affects people with poor immunity.
What causes herpes zoster?
After primary infection—varicella—VZV remains dormant in dorsal root ganglia nerve cells in the spine for years before it is reactivated and migrates down sensory nerves to the skin to cause herpes zoster.
It is not clear why herpes zoster affects a particular nerve fibre. Triggering factors are sometimes recognised, such as:
- Pressure on the nerve roots
- Radiotherapy at the level of the affected nerve root
- Spinal surgery
- An infection
- An injury (not necessarily to the spine)
- Contact with someone with varicella or herpes zoster
What are the clinical features of herpes zoster?
The clinical presentation of herpes zoster depends on the age and health of the patient and which dermatome is affected.
The first sign of herpes zoster is usually pain, which may be severe, relating to one or more sensory nerves. The pain may be just in one spot or it may spread out. The patient usually feels quite unwell with fever and headache. The lymph nodes draining the affected area are often enlarged and tender.
Within one to three days of the onset of pain, a blistering rash appears in the painful area of skin. It starts as a crop of red papules. New lesions continue to appear for several days within the distribution of the affected nerve, each blistering or becoming pustular then crusting over.
The chest (thoracic), neck (cervical), forehead (ophthalmic) and lumbar/sacral sensory nerve supply regions are most commonly affected at all ages. Frequency of ophthalmic herpes zoster increases with age. Herpes zoster occasionally causes blisters inside the mouth or ears, and can also affect the genital area. Occasionally there is pain without rash—herpes zoster "sine eruptione"—or rash without pain, most often in children.
Pain and general symptoms subside gradually as the eruption disappears. In uncomplicated cases, recovery is complete within 2–3 weeks in children and young adults, and within 3–4 weeks in older patients.
What are the complications of herpes zoster?
Herpes zoster may cause:
- Involvement of several dermatomes or bilateral eruptions
- Deep blisters that destroy the skin, taking weeks to heal followed by scarring
- Muscle weakness in about one in 20 patients. Facial nerve palsy is the most common result. There is a 50% chance of complete recovery but some improvement can be expected in nearly all cases
- Infection of internal organs, including the gastrointestinal tract, lungs and brain (encephalitis)
Herpes zoster in the early months of pregnancy can harm the fetus, but luckily this is rare. The fetus may be infected by chickenpox in later pregnancy, and then develop herpes zoster as an infant.
Post-herpetic neuralgia is defined as persistence or recurrence of pain in the same area, more than a month after the onset of herpes zoster. It becomes increasingly common with age, affecting about a third of patients over 40. It is particularly likely if there is facial infection. Post-herpetic neuralgia may be a continuous burning sensation with increased sensitivity in the affected areas or a spasmodic shooting pain. The overlying skin is often numb or exquisitely sensitive to touch. Sometimes, instead of pain, the neuralgia results in a persistent itch (neuropathic pruritus).
Treatment of herpes zoster
Antiviral treatment can reduce pain and the duration of symptoms if started within one to three days after the onset of herpes zoster. Aciclovir 800 mg 5 times daily for 7 days is most often prescribed. Valaciclovir and famciclovir are also effective. The efficacy of prescribing systemic steroids is unproven.
Note that herpes zoster is infectious to people who have not previously had chickenpox.
Management of acute herpes zoster may include:
- Rest and pain relief
- Protective ointment applied to the rash, such as petroleum jelly.
- Oral antibiotics for secondary infection
Post-herpetic neuralgia may be difficult to treat successfully. It may respond to any of the following.
- Local anaesthetic applications
- Topical capsaicin
- Tricyclic antidepressant medications such as amitriptyline
- Anti-epileptic medications gabapentin and pregabalin
- Transcutaneous electrical nerve stimulation or acupuncture
- Botulinum toxin into the affected area
Nonsteroidal anti-inflammatories and opioids are generally unhelpful.
Prevention of herpes zoster
Because the risk of severe complications from herpes zoster is more likely in older people, those aged over 60 years might consider zoster vaccine, which can reduce the incidence of herpes zoster by half. In people who do get herpes zoster despite being vaccinated, the symptoms are usually less severe and post-herpetic neuralgia is less likely to develop.