Post-herpetic neuralgia is a condition caused by shingles, which is a reactivation of the varicella zoster virus that causes chickenpox. Shingles develops along the path of one nerve. It most often appears many years after the initial chickenpox infection. Shingles most often presents as a very painful and blistering rash on the skin, which may take weeks to heal. In post-herpetic neuralgia, the pain persists long after the rash has healed. Most cases are brought under control with various medications. In other cases injections or spinal cord stimulation may be necessary to control pain.