Postherpetic Neuralgia (PHN): An Overview
Herpes zoster (shingles) and the potential sequela (PHN) are caused by the same virus that causes chicken pox1,2
Chicken pox is the primary risk factor for shingles and subsequent postherpetic neuralgia (PHN) pain1,2
- 95% of Americans have had chicken pox1
- Approximately 1 million new cases of herpes zoster (HZ; shingles) in the United States each year1,2
- HZ can occur at any age
- Incidence increases with age3
- Approximately 120,000 to 200,000 PHN cases annually in the United States1
- For patients <27 year of age, a population-based study by Hope-Simpson found that none of the patients who developed herpes zoster experienced PHN. For patients between the ages of 50 and 59, the incidence was 7.4%; however, that number nearly tripled for patients in the 60-69 age group and continued to increase in subsequent decades. By the age of 80, over a third of patients diagnosed with shingles went on to develop PHN16
- Risk factors include: presence of a prodrome, severe acute pain, severe HZ rash within 3 days of HZ infection2,4
PHN pain presents with multiple pain qualities, making it difficult to diagnose5,6
- As many as 80% of PHN patients may be mis-diagnosed7
- Clinical features of PHN pain include: burning, stabbing, shooting, abnormal sensations, sensory loss, allodynia, hyperalgesia5,6
- PHN can severely impact patients' lives2,8
PHN can occur anywhere on the body, and sometimes in more than one place9
- Most commonly occurs on the torso (chest and back), waistline, upper arm, or face
Shingles Causes and Symptoms
Shingles, or herpes zoster, is a disease caused by reactivation of the varicella zoster virus (VZV) that has remained dormant in the dorsal root ganglia following a prior systemic VZV infection, such as chicken pox.10
Upon reactivation of the latent herpes zoster virus by advancing age or immunosuppression, a severe inflammatory response is initiated within the dorsal root ganglion10 Reactivated viral particles multiply and spread along sensory axons to the skin's surface, producing the characteristic, and usually painful, vesicular rash of acute herpes zoster in the distribution of the affected dermatome.11
As the virus spreads, inflammation occurs and usually leads to complications such as demyelination and sclerosis. Peripheral afferent nerves, as well as the dorsal root ganglia and central nervous system, may be irreversibly damaged.10
The rash does not cross the midline and is generally confined to the area of skin innervated by a single sensory ganglion (i.e., a single dermatome). Skin lesions typically resolve within approximately 4 weeks after rash onset.12
Over one million Americans are afflicted with shingles each year, and roughly 20 percent of those diagnosed with shingles develop postherpetic neuralgia (PHN),1 the most common and debilitating sequela of shingles.11
Postherpetic Neuralgia (PHN)
There are varying opinions as to how much time must elapse following acute zoster outbreaks before pain is definitively termed postherpetic neuralgia (PHN); however PHN is commonly defined as pain that persists or occurs at least one month after acute herpes zoster.10,11
In damaged peripheral nerve axons, as in the case of PHN, there is an increase in the number of sodium channels which function abnormally at the sites of peripheral nerve injury. These abnormally functioning sodium channels are thought to result in foci of ectopic impulses and the spontaneous transmission of pain signals.13
Over time, excessive firing of injured peripheral nerves can lead to central sensitization and increased excitability of the second order neuron.14,15
Patients with PHN may present with one or more of the following10:
- A constant burning, throbbing, or deep aching pain
- An intense, intermittent pain with a lancinating or jabbing quality (may be spontaneous)
- A dysesthetic pain, known as allodynia, that is evoked by normally innocuous stimuli such as light touch or exposure to heat or cold 1,12
Sensory abnormalities such as numbness, itching, altered sensation, and sensory deficits are often present in the affected region, as are areas of skin pigmentation change and/or scarring from the zoster rash.10
While the pain of PHN resides in the area of the prior herpes zoster rash, the size of the affected region can vary considerably, from small, discrete regions within the involved dermatome, to larger areas that extend beyond the margins of the initial skin rash and involve other dermatomes.10
It is believed that this extended hypersensitivity may reflect dynamic changes within the central nervous system associated with peripheral nerve damage.10
Online Resources
Learning more about after-shingles pain is as easy as 1, 2, 3... you can visit the LIDODERM® Online Resource Page for additional information.
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