There’s something you don’t see everyday

Endometriosis in a man. Yep, thats right, it is an incredibly rare occurrence but it has been known to happen. This, particularly detailed, report comes from Japan and concerns a 69 year old man who had been undergoing estrogen therapy for 9 years to treat prostate cancer. In the abstract no account of the symptoms are given, but it does state that the man was found to have a series of endometriotic cysts measuring approximately 5x3cm in the left paratestis (the region just above the testicle).

The authors state that this may have occurred due to, what is known as, endometriotic metaplasia or stromal hyperplasia. Basically, what both of these terms mean is that, under the influence of increased estrogen levels, the normal tissue has undergone a change into a different tissue type.

This case report isn’t the first to observe endometriosis in a man; it’s not even the first report of it occurring in this area of the body.

Other than that there have only been six other cases of male endometriosis reported in locations such as the bladder, prostate and lower abdominal wall. However, if we look at all of these cases, most of them have one thing in common; they have been undergoing long term estrogen therapy for the treatment of prostate cancer. This is quite important, as unusual presentations of a disease can often give us clues as to how it arises in women.

One of the reports of male endometriosis was from a young man aged 27 who was otherwise completely healthy, very different to the other reports which are mostly much older men with prostate cancer. So not only was this an unusual presentation of endometriosis, it was an unusual, unusual presentation, if that makes sense. So what can this tell us about the disease as a whole?

The authors of this report looked to the very beginning of the development of the reproductive organs. Whilst still only a developing embryo, there are different structures that will form the male and female reproductive systems (there’s a nice illustration here). The female organs develop from the müllerian duct which in male embryos regresses because the embryo produces the imaginatively named müllerian inhibiting substance (MIS). The authors of this report suggest that exposure to certain environmental toxicants (such as diethylstilbestrol or other hormone disrupters) whilst the embryo is still developing, may lead to abnormal production of MIS which in turn stops the müllerian duct regressing properly, leaving small remnant patches of tissue that could, given the right stimulus, develop into endometrial like tissue, which would appear as endometriosis.

Could something similar explain endometriosis in women? Well there could be if this ties in with the theory of mullerian rest. This theory states that during normal foetal development, tiny parts of the mullerian duct, perhaps only a few cells, get displaced and deposited on other organs. Once there, the displaced deposits do nothing until stimulated to transform into endometriotic tissue later in life. What these exact stimuli are, or why some women experience this displacement are mysteries, as yet, unsolved, but answering these questions may be a defining moment in the history of endometriosis.