Post Herpetic Neuralgia (PHN), is a pain condition that caused by varicella zoster virus, the same virus which causes chicken pox. After the symptoms of chickenpox gone, the virus "goes to sleep". When the immune system goes down, the virus wake up and grows in nerves, causing pain. When the virus reaches the skin, it causes the shingles rash. Interventional Therapies such as Nerve Blocks, Sympathetic Blocks, Spinal Cord Stimulation for PHN. Source by bradfordshalond