A healthy 65-year-old woman developed a relentless burning feeling in her mouth that stumped doctors and dentists for months before its strange cause was found, according to a recent report of her case.
The burning got worse whenever the woman brushed her teeth but subsided within 10 minutes. The pain went away after one month after she first experienced it, but then returned a year later and remained constant. She saw a dentist, an oral surgeon and her family doctor, but none of them could find any lesions in the mouth or other possible causes of the burning.
They prescribed mouthwashes, milk-of-magnesia rinses and anti-anxiety drugs, and recommended avoiding toothpaste with whitening agents. But nothing relieved the burning sensation.
The woman had a case of a condition called "burning mouth syndrome," which is a chronic, burning sensation inside the mouth, usually in the lips, tongue or palate, according to the study, published April 1 in the journal BMJ Case Reports. [16 Oddest Medical Case Reports]
"It's common in postmenopausal women, and affects up to 7 percent of the general population," said study co-author Dr. Maria Nagel, a neurovirologist and professor at the University of Colorado School of Medicine in Aurora. Nagel compared the feeling to a "sunburn inside the mouth," adding that it feels similar to the pain caused by a tooth infection or a root canal.
The condition can be a side effect of certain drugs, but other cases have no apparent medical or dental cause, Nagel said.
After the woman had experienced this pain for six months, doctors tested her saliva for the virus that causes oral herpes, the herpes simplex virus type 1 (HSV-1). The virus commonly causes cold sores around the mouth and lips, but the woman didn't have any cold sores.
The tests showed that the woman's saliva was swarming with the infectious particles.
"If she'd had cold sores, it would have been obvious," Nagel told Live Science. "Most people don't think of HSV-1 as the potential cause of burning mouth syndrome, so they don't test for it. But it's easily treatable with antiviral medication," she said.
The woman began taking an antiviral drug, and her pain disappeared within five days. Follow-up tests of her saliva -- done four weeks later, and again six months later -- found no hint of the virus. A year and a half after finishing her treatment, the patient remains pain-free, researchers said.
Estimates vary, but up to 70 percent of people worldwide may be infected with HSV-1, Nagel said. This herpes simplex virus is spread through kissing, intimate contact, or sharing objects such as toothbrushes or towels, according to the Centers for Disease Control and Prevention. In most infected people, the virus never becomes activated, Nagel said. When the virus is activated -- typically due to stress or a suppressed immune system -- it usually causes cold sores that eventually go away on their own.
But sometimes, the virus can reactivate without causing cold sores, as this woman's case demonstrates. Instead, it infects the facial nerves, most commonly the trigeminal ganglion, which provides sensation in the face and mouth, Nagel said.
Nagel and her colleagues still don't know why the herpes virus reactivated in the woman, but they speculated that it might have been due to hormonal fluctuations, because she was postmenopausal.
HSV-1 may be the culprit for a number of unexplained medical symptoms besides burning mouth syndrome. For example, Nagel and her colleagues have found preliminary evidence that the virus can cause migraine headaches, and patients get relief from taking antiviral medication.
In rare cases, the virus can cause encephalitis, a type of brain inflammation that can cause significant brain damage or death if not treated promptly, according to the Mayo Clinic.
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