iStock/Getty Images Plus Only around 100 instances of Foreign Accent Syndrome have been documented.

A rare form of prostate cancer came with an even rarer side effect: an Irish accent. As a new study published in January revealed, an unnamed American man in his 50s developed an "Irish brogue" almost two years after his cancer diagnosis, despite having never been to Ireland.

This strange condition is known as Foreign Accent Syndrome (FAS), and though this is not the first instance of FAS in history, it is only the third time it's been linked to cancer, and the first time it's been linked to prostate cancer.

It's important to note that FAS isn't exactly what it sounds like. Those afflicted with FAS aren't really taking on an accent per se — rather, they are experiencing a neurological dysfunction that alters their speech patterns. To a listener, however, this change often sounds identifiably foreign. In this instance, that change happened to sound Irish.

The man's case was documented in a paper published in BMJ Case Reports last month. According to the paper, the 50-year-old patient had been dealing with metastatic prostate cancer for some time when he suddenly developed "an uncontrollable ‘Irish brogue' accent despite no Irish background."

Most often, cases of FAS occur as the result of a stroke or traumatic brain injury, but this instance was different.

"He had no neurological examination abnormalities, psychiatric history, or MRI of the brain abnormalities at symptom onset," the report reads. "Imaging revealed progression of his prostate cancer, despite undetectable prostate-specific antigen levels. Biopsy confirmed transformation to small cell neuroendocrine prostate cancer (NEPC)."

NEPC is a highly aggressive, often fatal cancer variant. Per the report, NEPC continued to spread in the patient despite his treatment. Doctors believe that the patient developed FAS as the result of an underlying paraneoplastic neurological disorder — brain damage caused by the body's immune system responding to cancer somewhere else in the body.

Basically, in trying to fight the cancer, his immune system caused damage to his brain, which led him to speak with an accent that sounded Irish.

Gizmodo reported that FAS was first described by doctors in 1907, and only around 100 cases have ever been documented in medical literature.

In other recorded instances of FAS, patients' accents faded as their brains recovered from injury. Unfortunately, the man in this case died from his cancer as the metastases reached his brain. His accent persisted until his death.

Only two other cases of FAS linked to cancer have been referenced in medical literature before this.

A 2008 case study documented the "unique case of a 60-year-old female who developed FAS secondary to metastatic breast carcinoma." A similar report in 2013 examined the case of a 50-year-old Italian woman who developed a "strange accent" that altered the rhythm and body of her speech.

Perhaps the most famous case of FAS, however, happened shortly after World War II.

According to The Atlantic, this case involved a Norwegian woman named Astrid who was struck by shrapnel during a raid. Two years later, she spoke to neurologist Georg Herman Monrad-Krohn, who wrote that she had "such a decided foreign accent that I took her for German or French," even though she, naturally, spoke Norwegian fluently.

The unfortunate result was that, given the events of World War II, numerous others also mistook Astrid for being German, which led to her being ostracized in the community.

"She complained bitterly of constantly being taken for a German in the shops, where consequently the assistants would sell her nothing," Monrad-Krohn wrote.

At the time, Monrad-Krohn referred to the condition as "dysprosody." The term "prosody" refers to the patterns of stresses and intonations in a person's speech — things that go beyond the words themselves, that is.

In Astrid's case, these elements were still present. She was able to inflect, stress certain parts of sounds, and speak in different rhythms, but these elements differed greatly from those of a native Norwegian speaker.

It wasn't until 1982 that the term "Foreign Accent Syndrome" was coined by neurolinguist Harry Whitaker.

"Vowels are particularly susceptible: which vowel you say depends on where your tongue is in your mouth," explained Lyndsey Nickels, a professor of cognitive science at Macquarie University, in a piece for The Conversation. "Different languages have different vowels, and within a language one of the main differences between accents is in the vowels. Aussies accuse Kiwis of saying ‘fush and chups' and Kiwis of Aussies ‘feesh and cheeps'!"

One commonality among patients afflicted with FAS, Nickels said, was difficulty producing vowels. The brain damage that caused FAS essentially impairs their ability to control the movement of their tongue, leading them to "overshoot" or "undershoot" its placement when making vowel sounds. Because their vowels sound different, it often sounds like a foreign accent.

"People with foreign accent syndrome don't speak with all the features of a foreign accent, but there are enough things about the way they speak to make it seem as though they have a different accent," Nickels wrote.

In almost every instance, study authors and researchers looking into FAS agreed that more research is needed to fully understand how this rare condition develops.

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