Herpes Zoster

- aka Shingles
- Occasionally the herpes virus infects a dorsal root ganglion.  This causes severe pain in the dermatomal segment subserved by the ganglion, thus eliciting a segmental type of pain that circles halfway around the body.  The disease is called herpes zoster, or "shingles", because of a skin eruption that often ensues.
- The cause of the pain is presumably infection of the pain neuronal cells in the dorsal root ganglion by the virus.  In addition to causing pain, the virus is carried by neuronal cytoplasmic flow outward through the neuronal peripheral axons to their cutaneous origins.  Here the virus causes a rash that vesiculates within a few days and then crusts over within another few days, all of this occurring within the dermatomal area served by the infected dorsal root.

- Primary infection with the varicella zoster virus causes chickenpox.  Following recovery, the virus remains dormant within dorsal root ganglia.  Reactivation of the virus leads to shingles, which involves the dermatome supplied by the sensory nerve affected.  Severe pain and a rash similar to chickenpox, often confined to one of the divisions of the trigeminal nerve, or to a spinal nerve dermatome, are diagnostic.  Herpes zoster involving the geniculate ganglion results in a lower motor neuron facial paralysis, known as Ramsay Hunt Syndrome.  Occasionally, if the vestibulocochlear nerve is involved, there is vertigo, tinnitus and some deafness.



References:
1. Guyton, Arthur C., & Hall, John E. Textbook of Medical Physiology 11th Edition. 2006.