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What’s the straight dope about the correlation between vasectomy and dementia? —A concerned post-op patient, via e-mail

Can men who have had vasectomies have wet dreams? —Scott, via e-mail

Though even the idea of a scalpel nearing the upper inseam can make a guy shift uneasily in his seat, vasectomy is a very safe and effective means of minimizing unwanted procreation: Complications are relatively rare and minor, and, for obvious structural reasons, it’s way less invasive than the female analog, tubal ligation. But it’s still surgery, which always entails some risk; if said risk might include future mental impairment, a little concern seems understandable.

What we’re referring to here is a December 2006 study by a team from Northwestern University focusing on men with a fairly uncommon form of dementia called primary progressive aphasia. Unlike Alzheimer’s, for instance, PPA doesn’t result in memory loss but instead affects regions of the brain associated with language use—it typically shows up first as difficulty in thinking of the word you want (uh-oh, a lot of readers just said to themselves) but may ultimately lead to serious across-the-board problems with written or spoken communication.

It’s also more common in men than in women (with memory-related dementia the reverse is true), and apparently it was a patient of lead researcher Sandra Weintraub who first wondered about a connection between his vasectomy surgery and the onset of PPA. Intrigued, Weintraub et al rounded-up two groups of 55- to 80-year-old men, PPA patients and unimpaired volunteers, and compared their vasectomy rates. Results: members of the PPA group were more than twice as likely to have had a vasectomy than the non-PPAers; within the PPA group, on average the vasectomy recipients developed dementia earlier than their unsterilized peers.

Which, admittedly, is creepy. There are, though, some important reasons not to start freaking out just yet. First, the sample size for the study was quite small—just 47 guys with PPA, 57 without. Given that every year for decades now a half million men or more have undergone the procedure; clearly we’ve got lots of subjects we could be looking at (and, in so doing, not rely as heavily on those who’ve already developed PPA). So far, though, no one’s reproduced the NU team’s results.

And second, the researchers themselves can only guess at what might account for a vasectomy-PPA link. In order to keep the male body’s autoimmune system from attacking its sperm cells, the testes are isolated from the flow of blood by something called (reasonably) the blood-testis barrier. But in testicular surgery this firewall is often breached, allowing contact between sperm and blood cells and, in fact, one very common side effect of vasectomy is that the patient develops antibodies to his own sperm. Since other kinds of antibodies have been known to make their way into the brain and cause real trouble there, Weintraub speculates that the antisperm antibodies resulting from vasectomy may be doing something similar. (The study also proposes that women might develop such antibodies and thus a greater risk of PPA; if so, since the overall number of women exposed to sperm is pretty high, one might think PPA would be more common in females than it is.)

The Northwestern docs stressed that further research was required before sounding the alarm, and let’s remember that some earlier vasectomy-related fears turned out to be largely unfounded. At one point, for instance, many believed the procedure might increase the incidence of prostate or testicular cancer, but according to the National Cancer Institute, any connection is pretty weak.

A better-documented side effect is sometimes known as postvasectomy pain. Unlike the normal, typically minor pain that often follows surgery, PVP can occur years after the procedure, ranging in intensity from mild to excruciating and arising from a number of conditions: high-pressure sperm buildup (the surgery doesn’t halt production of sperm, just keeps it out of the ejaculate), accumulated sperm granulomas (hard balls of tissue that form around stray sperm), kinked tubes, etc. Some sources say as many as a third of all patients experience PVP, but one Journal of Andrology survey suggests it’s less than 10 percent. Vasectomy reversal can often stop the pain, though researchers aren’t entirely sure why. Frankly, you kind of wish they were.

Now, Scott, let me ask you one: How old are you? Because your question doesn’t sound like something that would occur to anyone with any business contemplating elective surgery. The answer happens to be yes, vasectomy recipients can have wet dreams. However, little research has been done on the subject for the simple reason that who cares? People preoccupied with wet dreams tend to be teenage boys and, no matter how concerned they may be about contraception, very few opt to go under the knife. Plenty of factors might sensibly lead a guy to consider a vasectomy but being too embarrassed to buy condoms isn’t one of them.

Comments, questions? Take it up with Cecil on the Straight Dope Message Board, straightdope.com, or write him at the Chicago Reader, 11 E. Illinois, Chicago 60611.