How does PHN present?
PHN presents as pain in the area where an acute herpes zoster infection was present. Although the rash and vesicles of the acute herpes zoster infection have healed, scarring in the area may still be present. The area of pain is unilateral, never crossing over the midline, and usually mimics the distribution of the acute herpes zoster pain. The thoracic and ophthalmic division of the trigeminal nerve is most commonly involved, followed by the lumbar and sacral areas. However, the pain is sometimes in small, discrete locations, and may sometimes spread to areas outside the initial acute herpes zoster infection (see below). The patient’s pain complaints are varied and numerous, rang-ing from mild, aching pain, to severe, burning, lancinating pain. The pain may be constant or intermittent, and may be provoked by touch, activity, or stress. The patient may complain of extreme hyperesthesia (increased sensitivity), hyperpathia (increased pain to a painful sensation), or allodynia (pain to a nonpainful stimulus) in the area, and may also present with pain over an area of numbness. The pain of PHN may be so severe as to push the patient to suicide and is a known cause of suicide in the elderly population.
The fact that there are so many different types of pain means that there are most likely multiple mechanistic reasons why patients develop pain, including sensitization and/or loss of peripheral nerve endings, damage to periph-eral axons and the dorsal horn, ectopic firing of peripheral afferent nerves, infiltration of peripheral nerves with chronic inflammatory cells, and damage to the central nervous system. In addition, some investigators believe that central “wind-up” occurs, causing spreading of the painful area, as well as hyperesthesia.