THERE is a bit of Geordie in Karen Butler’s accent, a dash of South African, and still a trace of the vampire that most alarmed her family when she came home from the dentist a changed woman.

Mrs Butler is a 56-year-old tax accountant and mother of five from western Oregon who had never been outside the United States before undergoing extensive oral surgery a year and a half ago. She still has not been abroad. She just sounds as if she has.

Her story began with a severe case of gingivitis – inflammation of the gum that can eventually attack the jawbone. “Vanity was overridden by necessity so I made arrangements for Dr [Gregory] Herkert to pull all mah upper teeth and make me a set of dentures,” she said in a recent interview transcribed as accurately as possible by The Times.

The doctor chose an anaesthetic, Halcion, that leaves patients able to respond to simple instructions but with no memory of the procedure.

“So to me I vent to sleep, and ven I woke up I had this accent,” Mrs Butler said. “It was just night and day.” It was initially more night than day, in that one of her younger daughters decided she sounded “Transylvanian” and persuaded her mother to record the words “I vant to suck your blood” as a ringtone for her mobile phone. The town of Toledo, Oregon, has since reached a consensus that Mrs Butler’s new accent is in fact British, or at least what Ted Lowenkopf, a local neurologist, called “an amalgam of different-sounding speech” that sounds more British than anything else.

Dr Lowenkopf met Mrs Butler for the first time last week and diagnosed foreign accent syndrome, a condition so rare that it could be mistaken for a parody of rare syndromes, but is real. One of the earliest recorded cases was that of a Norwegian woman injured by shrapnel in a Luftwaffe raid on Oslo in 1941, who was left with a German accent and ostracised for it by suspicious compatriots. More recently, Sarah Colwill, from Devon, emerged from a severe migraine with a strong Chinese accent.

This much is clear: Mrs Butler no longer speaks with Oregon’s distinctive combination of broad and short vowels, or with the “high rising terminal contours” (statements that sound like questions) common to many dialects of the Pacific North West.

Instead, she sounds like a soft-spoken Johannesburger transplanted to Newcastle upon Tyne by way of Brasov. Dr Lowenkopf’s best guess is that while having her teeth out she suffered a minor injury to the tiny part of the brain that controls speech intonation and articulation.

“I appear to be completely normal otherwise,” Mrs Butler said. She admits that some of her clients have found the change distressing, but insists that she cannot hear it herself. “Everything works,” she said. “It just works odd.”