Postherpetic neuralgia (PHN) is a common pain syndrome that can transpire after an episode of herpes zoster (HZ). HZ, also known as shingles, is the reactivation of latent varicella zoster virus (VZV) that remains in the dorsal root ganglion. The virus typically reactivates years after the primary infection. It is clinically defined as a dermatomal prodrome of severe pain followed by the development of cutaneous lesions. The lesions involved are grouped vesicles that are in various stages of evolution with erythematous bases spread within a sensory dermatome. In order to understand how to treat PHN it is important to know the incidence, epidemiology, and pathophysiology of HZ.
Incidence and Epidemiology
The incidence of HZ in the United States is four cases per 100 000 annually. In those who are 60 years of age and older the rate increases to 10 per 100 000. This amounts to approximately 1 in three US citizens that will develop HZ in their lifetime. Epidemiologically, the reactivation of VZV classically happens in those with certain risk factors. Those factors include immunocompromise secondary to infection, such as human immunodeficiency virus (HIV), and medications, including chemotherapy, high-dose steroids, and posttransplant immunosuppressants. Individuals with white blood cell malignancies such as leukemia and lymphoma also have a higher chance in reactivating VZV. Older age, however, is one of the main risk factors. One theory is attributed to the waning of specific cell-mediated immune response to VZV as an individual becomes older.
After the reactivation of VZV, there is a prodromal phase where the patient experiences severe pain with dysesthesia along a single sensory dermatome. Areas that are more characteristically affected are the thorax, face, neck, scalp, and extremities. Within 3–7 days of the prodromal phase a pathognomonic vesicular rash appears in the same sensory dermatome. Typically the rash does not cross the midline and stays within one dermatome, however, there have been reports of rashes extending beyond one and reaching two to three dermatomes. With no treatment the rash usually disappears within 2 weeks of the initial eruption for healthy patients. Severity and risk of complications, such as superinfection or dissemination, have a significant proportional relationship with the age of the patient and the degree of immunocompromise.
Currently, there is a live HZ vaccine approved for patients 60 years of age and older. This vaccine has shown to decrease the lifetime risk of having HZ from 20% to 10%. It has also shown to decrease the rate of PHN.
Treatment of HZ is especially critical for immunocompromised patients and those in the upper extremity of the age spectrum. Approximately, 96 deaths are recorded annually with HZ being the primary cause in said populations. The best possible outcome is ...