Many myths and legends probably have a basis in fact. For example, the ancient tale of a great flood, recorded in the Babylonian Epic of Gilgamesh around 2000 B.C. and later in the Biblical tale of Noah, probably refers to a cataclysmic deluge that occurred in the Middle East many millennia ago.

Similarly, ancient tales of witchcraft, vampires, werewolves, and other assorted phenomena may have come from superstitious misunderstanding of the natural world. People with epilepsy, for example, were thought to have been possessed by demons or to be under the spell of witches. Acromegaly, a chronic disease of the pituitary gland that causes over-secretion of growth hormone, results in enlargement and distortion of many parts of the skeleton, and may be responsible for stories of misshapen giants such as Goliath in the Bible and the boy-eating ogre in the tale Jack and the Beanstalk.

The ancients believed that the birth of a child with physical deformities was a sign of evil. The word "monster" itself comes from the Latin word "monstrum," meaning omen or portent.

But with the rise of evidence-based science in the 19th and 20th centuries, fear of the unknown began to wane, as exemplified in Dracula. The book represents "a conflict between a modern way of looking at the world and an ancient one," says Carol Senf, PhD, professor of literature, communication and culture at Georgia Institute of Technology in Atlanta. "I think that Stoker, two of whose three brothers were physicians, was interested in thinking about that. He's up on transfusions for example, and he's up on all kinds of scientific stuff."

Yet the death of Dracula -- with a stake right through his old undead ticker -- didn't end the legend of the vampire. It lives on in countless (no pun intended) movies, comic books, and even in the persona of the obsessive enumerator Count Von Count from Sesame Street.

Nor are vampires the only reality-based specters that still haunt our imaginations. Werewolves really exist -- or at least they do in the minds of people with the rare psychiatric disorder known as lycanthropy.

In the March 2000 issue of the Canadian Journal of Psychiatry, J. Arturo Silva, MD and Gregory B. Leong, MD describe the case of "Mr. A" who suffered from a case of partial lycanthropy -- the delusion that one is being transformed into a wolf.

"Mr. A is a 46-year-old male who experienced delusional episodes that lasted up to several hours. During these episodes, he had sensations of hair growth on his face, trunk, and arms.

Occasionally, he became convinced that the hair growth was real. He also complained that he experienced structural facial malformations and lesions that took place within minutes and remained for hours. He thought these changes would make him appear to be a wolf, and avoided seeing his face or body whenever possible.

However, he did not believe that he was a wolf. He denied that his mind was changing into a different mind or that he was a different person from his objective self."

Silva, who is a staff psychiatrist at the Veterans Affairs Medical Center in Palo Alto, Calif., tells WebMD that lycanthropy, "can be due to a hysteria or a psychosis -- in other words madness -- or it can be due to other kinds of illnesses, such as depression associated with a lot of self-deprecating thoughts. But often, once you start getting into a real belief system where somebody says 'I think I'm turning into a werewolf,' and he looks at his body and his hair, and the shape of his face changing -- once you get to that level it usually is a clear loss of contact with reality."

Silva says that lycanthropy is uncommon today -- probably because we've killed or banished most of the wolves to the remote wilderness and thus no longer live among them. However, people in other cultures in other parts of the world suffer from similar delusions, involving other types of animals, such as crocodiles or eagles.

Such transformations may seem to be the stuff of fantasy, but they still occur every year. If you don't believe it, just open your door this Halloween.

Originally published Oct. 29, 2001.
Medically reviewed Oct. 16, 2002.