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Page: Pathophysiology
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Postherpetic neuralgia is thought to result after nerve fibers are damaged during a case of Herpes Zoster (also known as Shingles). Damaged fibers cannot send electrical signals from the skin to the brain as they normally do, and may be erratic or exaggerated, causing chronic, often excruciating pain that may persist or recur for months — or even years — in the area where shingles first occurred.
Some patients with PHN appear to have abnormal function of unmyelinated nociceptors and sensory loss (usually minimal). Pain and temperature detection systems are hypersensitive to light mechanical stimulation, which causes severe pain even from gentle touch or pressure (allodynia). Allodynia may be related to formation of new connections involving central pain transmission neurons.
Other patients with PHN may have severe, spontaneous pain without allodynia, possibly secondary to increased spontaneous activity in deafferented central neurons or reorganization of central connections. An imbalance involving loss of large inhibitory fibers and an intact or increased number of small excitatory fibers has been suggested. This input on an abnormal dorsal horn containing deafferented hypersensitive neurons supports the clinical observation that both central and peripheral areas are involved in the production of pain.
Frequency
Each year, approximately 1,000,000 individuals in the United States develop shingles, or herpes zoster. Approximately 20 percent of these shingles patients, or 200,000 individuals, go on to suffer from PHN, or post-herpetic neuralgia.
Mortality/morbidity
* The condition is not fatal.
* Patients may suffer significant pain for a prolonged period of time.
* Older age appears to be the most significant risk factor for developing PHN.
Predisposing factors
* Sex: No predilection for developing PHN is known.
o Although 65% of patients were women in a study by Watson et al, this was believed to mirror the usual predominance of women in this age group.
* Age: The association between greater age and PHN is strong.
o At age 60, approximately 60% of patients with shingles develop PHN, and at age 70, 75% develop PHN.
* Race: It may influence susceptibility to herpes zoster. Blacks are one fourth as likely as whites to develop this condition.
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Important notice:
The content is not intended to be a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other
qualified health provider with any questions you may have regarding a medical condition.
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