Postherpetic neuralgia has been defined as pain that lasts after the acute herpes zoster rash has healed. Different studies, however, have recast the meaning in varying ways, sometimes defining PHN as pain lasting a specified time after rash healing, as well as lasting various times after rash onset.
12 The pain of PHN takes many forms, including dysesthesia, an unpleasant abnormal sensation, spontaneous or evoked; allodynia, pain evoked by a normally innocuous stimulus; and hyperalgesia, pain of exaggerated severity in response to normally painful stimulation.
14,15 The pain itself has been described as “tender,” “hotburning,” “stabbing,” “throbbing,” “shooting,” and “sharp.”
16 The pain is generally least severe in the morning and progresses in severity throughout the day; this pattern is maintained even when medication is used to manage the pain and may contribute to problems sleeping.
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Postherpetic neuralgia is the third most common cause of neuropathic pain in the United States, behind neuropathic low back pain and diabetic neuropathy.
18 Postherpetic neuralgia is of varying duration and develops in 9% to 34% of individuals with herpes zoster, depending on the definition used and population studied.
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In a longitudinal study of 94 patients with herpes zoster judged to be at elevated risk for PHN because of the presence of acute herpes zoster pain more than 2 weeks after rash onset, 50% had PHN, defined as any pain at 3-month follow-up, whereas only 3% had pain judged to be “clinically meaningful” (score ≤30/100 on the pain visual analog scale).
16 At 6-month follow-up, 32% had PHN and 2% had “clinically meaningful” PHN.
16 Thus, for many individuals, PHN persists for at least 6 months after cessation of rash. In author's professional experience, postherpetic neuralgia has been noted to last years or for the duration of an affected individual's lifetime.
Postherpetic neuralgia is thought to result from permanent changes in the affected neurons and to be pathophysiologically distinct from the shorter-term pain of acute herpes zoster. At postmortem study of subjects who had had PHN, dorsal horn atrophy and changes in the sensory ganglion were found. The role of these changes in PHN is supported by their absence on the contralateral side of a patient's body (PHN being, like herpes zoster, unilateral) and in patients with acute herpes zoster pain but not PHN.
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