Post-herpetic neuralgia

Post-herpetic neuralgia (PHN) is defined as chronic pain (.3 months) with skin changes in the distribution of one or more sensory roots subsequent to herpes zoster infection. However, the variation in time scale describing persistent pain from 1 month after herpes zoster to 3–6 months after the rash onset or, in some cases, after the rash has resolved makes it difficult to compare the studies of PHN. Herpes zoster, also known as shingles, results from the reactivation of varicella zoster virus (VZV), a double-stranded DNA herpes virus, which persists in a clinically latent state in spinal and cranial sensory ganglia after primary infection with varicella (chickenpox)