Researchers found a “surprising” possible link between the procedure and a form of aphasia.

Vasectomy may be a risk factor for primary progressive aphasia (PPA) in men, say researchers at Northwestern University Feinberg School of Medicine in Chicago.

They believe the procedure may induce immune responses to sperm, which shares antigenic epitopes with the brain.

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PPA is a neurological disease that causes trouble recalling and understanding words. Some patients lose the ability to express themselves and understand speech. It differs from typical Alzheimer’s disease in which a person’s memory becomes impaired.

The Chicago researchers surveyed 47 men with PPA who were being treated at Northwestern University’s Cognitive Neurology and Alzheimer’s Disease Center; 57 men with no cognitive impairment served as controls. All the participants ranged in age from 55 to 80 years. Of the non-impaired men, 16% had undergone a vasectomy, whereas 40% of the men with PPA had had the procedure.

“That’s a huge difference,” said lead study investigator Sandra Weintraub, PhD, professor of psychiatry and behavioral sciences. “It doesn’t mean having a vasectomy will give you this disease, but it may increase your chances of getting it.”

Dr. Weintraub and her colleagues, who published their findings in Cognitive and Behavioral Neurology (2006;19:190-193), also found that men who had undergone a vasectomy de-veloped PPA at a younger mean age (58 years) than men with PPA who had not had one (62 years).

In addition, they found preliminary evidence connecting frontotemporal dementia (FTD) to vasectomy. In a smaller group of 30 men with FTD, 37% had undergone a vasectomy. The earliest symptoms of FTD are personality changes, lack of judgment, and bizarre behavior. While Alzheimer’s disease is the most common form of dementia in men over age 65, the researchers found no increased rate among vasectomy patients.

Dr. Weintraub theorizes that a vasectomy may raise the risk of PPA and possibly FTD because the surgery breaches the blood-testis barrier, al-lowing semen to mix with blood. The immune system recognizes the sperm as invading foreign agents and produces antibodies in 60% to 70% of men. Dr. Weintraub said these antibodies might cross the blood-brain barrier and result in dementia.

“This is purely hypothetical. How-ever, there were studies in the 1970s, mostly done in animal models, showing there may be some cross-reactivity between sperm and brain antigens. Therefore: ‘Are the sperm antibodies not only attacking sperm, but do they also have an affinity for different brain tissue areas?’ ” Dr. Weintraub said.

She cautioned that her team’s preliminary and “surprising” findings need to be confirmed. “Right now, I don’t think urologists should tell their patients anything based on our findings. If we are able to determine that the vasectomy causes something that is harmful to the brain, then they can use those findings.”