An 82-year-old woman presented to the pain management office with severe right chest wall pain. The pain started 5 months ago, before an outbreak of vesicular rashes in the same distribution; however, the pain persisted after the lesions resolved. The pain radiated from the posterior to anterior thorax and was stabbing and burning in nature.
What is postherpetic neuralgia?
Postherpetic neuralgia (PHN) is a chronic pain syndrome that develops after an acute outbreak of varicella-zoster virus, also known as shingles. In acute herpes zoster, reactivation of dormant virus in a cranial or dorsal root ganglion leads to pain and a characteristic rash in the distribution of one or more dermatomes. Typically, the pain associated with acute herpes zoster resolves after approximately 1 month; however, approximately 10% of patients develop persistent pain, which if present after 4 months from rash onset is classified as PHN.
What is the pathophysiology of postherpetic neuralgia?
Pain during the acute episode of herpetic neuralgia is likely secondary to inflammation produced as viral particles move along nerves and damage affected neural structures. Sustained activity of primary afferent neurons supplying the dorsal horn may induce long-term potentiation of stimuli, known as central sensitization. Central sensitization along with neuronal degeneration is a likely pathophysiologic mechanism of PHN. Ongoing viral replication does not appear to be responsible for PHN.
What are the clinical manifestations of postherpetic neuralgia?
Patients with PHN typically present with sharp or burning pain over the distribution of thoracic, cervical, or trigeminal nerves, in the area of the resolved rash. Rarely, patients may experience radicular pain without a preceding rash. Allodynia, defined as pain resulting from a normally nonpainful stimulus, such as light touch, is nearly universal in patients with PHN. Areas of diminished or absent sensation to pain, touch, temperature, and vibration may also be present. PHN is associated with significant psychosocial dysfunction and decreased quality of life, especially in elderly patients.
What are the risk factors for development of postherpetic neuralgia?
Advanced age, greater rash severity, intensity of acute pain, deep pain at initial presentation, female gender, ophthalmic location, anxiety and depression, and allodynia have been described as predictors for the development of PHN.