Shingles is a painful blistering rash caused by reactivation of varicella zoster virus, the chickenpox virus. It is correctly known as herpes zoster.
Chickenpox or varicella is the primary infection with varicella zoster virus. During this widespread infection, which usually occurs in childhood, virus is seeded to nerve cells in the spinal cord, usually of nerves that supply sensation to the skin.
The virus remains in a resting phase in these nerve cells for years before it is reactivated and grows down the nerves to the skin to produce shingles (zoster). This can occur in childhood but is much more common in adults, especially the elderly.
Shingles patients are infectious (resulting in chickenpox), both from virus in the lesions and in some instances the nose and throat.
Anyone who has previously had chickenpox may subsequently develop shingles. They can be male or female, young or old. In general, it is more common in older adults and certainly tends to be more severe in this group. People who have had shingles previously rarely get it again (the risk of getting a second episode is about 1%).
Shingles is more common and more severe in patients with poor immunity. Blisters can occur in more than one area and the virus may affect internal organs, including the gastrointestinal tract, the lungs and the brain.
Chickenpox or shingles 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 devlop shingles as an infant.
It is not clear why shingles affects a particular nerve fibre. In some cases, it may be set off by pressure on the nerve roots, by radiotherapy at the level of the affected nerve root, by spinal surgery, by an infection such as sinusitis or by an injury (not necessarily to the spine).
Occasional clusters of shingles cases are reported. It is suggested that contact with someone who has chickenpox or shingles may cause one’s own virus to reactivate.
The first sign of shingles is usually pain, which may be severe, in the areas of one or more sensory nerves, often where they emerge from the spine. 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. Sometimes, especially in children, shingles is painless.
It starts as a crop of closely-grouped red bumps in a continuous band on the area of skin supplied by one, occasionally two, and rarely more neighbouring spinal nerves. New lesions continue to appear for several days, each blistering or becoming pustular then crusting over. Shingles occasionally causes blisters inside the mouth or ears, and can also affect the genital area.
The pain and general symptoms subside gradually as the eruption disappears. In uncomplicated cases recovery is complete in 2-3 weeks in children and young adults, and 3 to 4 weeks in older patients.
Occasionally pain is not followed by the eruption – shingles “sine eruptione”. These cases can be difficult to identify because there is no characteristic rash.
The chest (thoracic), neck (cervical), forehead (ophthalmic) and lumbar/sacral sensory nerve supply regions are most commonly affected at all ages but the frequency of ophthalmic shingles increases with age. Rarely the eruption may affect both sides of the body.
In elderly and undernourished patients the blisters are deeper. Healing may take many weeks and be followed by scarring. Muscle weakness arises in about one in twenty patients because the muscle nerves are affected as well as the sensory nerves. Facial nerve palsy is the most common result. There is a 50% chance of complete recovery and in time some improvement can be expected in nearly all cases.
Post-herpetic neuralgia is defined as persistence or recurrence of pain more than a month after the onset of shingles. It becomes increasingly common with age affecting about a third of patients over 40 and is particularly likely if there is facial infection. The pain may be continuous and burning with increased sensitivity in the affected areas, or a spasmodic shooting type, or, rarely, of an itchy, crawling variety. The overlying skin is numb or exquisitely sensitive to touch. Sometimes, instead of pain, the neuralgia results in a persistent itch (neuropathic pruritus).
If you think you may have shingles, see your doctor as soon as possible. Antiviral treatment can reduce pain and the duration of symptoms, but it is much less effective if started more than one to three days after the onset of the shingles
Because the risk of severe complications from shingles is more likely in older people, those aged over 60 years might consider zoster vaccine.
A herpes zoster vaccine has been produced which can prevent varicella zoster virus reactivation. The vaccine (called Zostavax®) is estimated to be 14 times more potent than the chickenpox vaccine and can be given to people aged 50 years or older. It should not be given to people with weakened immune systems. The herpes zoster vaccine can reduce the incidence of shingles by half. In people who do get shingles despite being vaccinated, the symptoms are usually less severe and after-pains are less likely to develop.