Herpes Simplex Virus and Bell Palsy

Infectious causes of acute facial nerve paralysis are numerous. Thus, involvement of the seventh nerve in its peripheral portion is well recognized as a complication of pyogenic meningitis, syphilis, and Lyme disease. In these conditions, the inflammatory process within the subarachnoid space is thought to involve the facial nerve, causing an acute inflammatory reaction and paralysis of the muscles that the facial nerve innervates.

The most clearly defined viral cause of acute inflammatory paralysis of muscles innervated by the facial nerve is varicella-zoster virus infection; this condition is known as the Ramsay-Hunt syndrome. In this condition, acute facial paralysis is associated with vesicles in the ear from which varicella-zoster virus can be readily recovered. The stereotypy of this condition leaves little doubt that varicella-zoster virus causes an acute inflammatory involvement of the facial nerve with paralysis of the muscles innervated by the nerve. This is often associated with seroconversion, as shown by an increase in specific antibody titer to varicella-zoster virus [1].

However, although the known causes of acute inflammatory facial paralysis are many, the most common cause of acute idiopathic facial paralysis (Bell palsy) is unknown. Considerable attention has been paid to the possibility that herpes simplex virus (HSV) might be the causative agent; this hypothesis was first suggested in 1972 by McCormick [2]. The hypothesis was based on the analogy that HSV was the cause of recurrent cold sores, in all likelihood related to the latency of the virus in trigeminal ganglia. McCormick suggested that HSV might be present in the geniculate ganglia, where it could cause a seventh nerve neuropathy when the virus traveled down the nerve axon, perhaps infecting the Schwann cells. Later studies confirmed the latency …