Cases in which the shingles rash does not appear are known as zoster sine herpete. In these instances, all symptoms of shingles except the rash are present, making early diagnosis more difficult, according to the New York Times Health Guide.
Shingles is caused by the varicella-zoster virus, the same virus responsible for chickenpox. After someone has chickenpox, the virus lies dormant in the nerve tissue. It remains inactive until it later emerges as shingles. Doctors are not certain why the virus becomes active again, but older people and those with compromised immune systems are most susceptible to the disease, notes eMedicine Health.