WASHINGTON (Reuters) - Men who have had a vasectomy may face an increased risk of developing a rare type of dementia marked by a steady loss of language skills, researchers said on Tuesday.

Researchers at Northwestern University in Illinois, writing in the journal Cognitive and Behavioral Neurology, linked this male sterilization surgery to a neurological condition called primary progressive aphasia, or PPA.

They surveyed 47 men with the condition being treated at Northwestern's Cognitive Neurology and Alzheimer's Disease Center, as well as 57 men who did not have PPA. Their ages ranged from 55 to 80.

Of those with primary progressive aphasia, 40 percent had undergone a vasectomy, compared to 16 percent of the others. Those with PPA also suffered the ailment an average of four years earlier than the others.

Preliminary data also linked vasectomies to another form of dementia involving behavioral changes. Among 30 men with frontotemporal dementia, more than a third had undergone a vasectomy, the researchers said.

Sandra Weintraub, who led the study, acknowledged that the research involved a small number of people and said she planned to conduct a larger national study to see if the findings hold up. In the mean time, she said her findings should not stop men from getting vasectomies.

"I was hoping not to, but unfortunately it's the kind of news that ends up scaring people even though they may not need to be scared," Weintraub said in an interview.

"This was just a clinical observation that started with one of my patients telling me that he first noticed the onset of his symptoms a couple of years after he had a vasectomy, and he wondered whether that might have something to do with it," Weintraub said. "In his mind, these things were connected."

Primary progressive aphasia, which affects people usually after age 50, can be mistaken for Alzheimer's disease since initial symptoms are similar. In this incurable disorder, nerve cells die in the brain region responsible for language skills.

It causes people's language capabilities to decline steadily, with symptoms such as faulty recollection of names of people and things, difficulties in speech, reading and writing, and poor comprehension.

A vasectomy is an operation in which the tubes through which sperm travels are cut, leaving sperm unable to reach the testes and making a man unable to impregnate a woman.

The study did not look at the mechanism behind any link between PPA and vasectomies, but Weintraub said it may be because the surgery allows sperm to leak into the blood. Antibodies produced by the immune system in response to the sperm might trigger damage that causes dementia, she said.