TORONTO -- As the COVID-19 pandemic dominated headlines this year, scientific research was often at the forefront.

The medical understanding of SARS-CoV-2 has evolved greatly since scientists first identified the novel coronavirus in Wuhan, China, more than a year ago. But short of widespread clinical studies, case reports of individual patients are a key part of early stage research, even if they are considered anecdotal.

Among the most popular sources for leading research is , considered "the world's largest repository of case reports."

Not surprisingly, seven of the journal鈥檚 top 10 most-read case reports in 2020 were related to COVID-19. But among the top five, three non-coronavirus case reports still attracted much attention. Here鈥檚 a roundup of the most-read case studies from the BMJ Case Reports, all of which were made freely available as part of the journal鈥檚 pandemic policy.

鈥業RREVERSIBLE鈥 HEARING LOSS AND COVID-19

This case study, which described the first U.K. case of hearing loss after COVID-19 infection, was picked up by more than 100 news outlets when it was published in October, according to BMJ Case Reports data. This type of hearing loss, officially known as 鈥渟udden onset sensorineural hearing loss鈥 (SSNHL), is not a new condition for otolaryngologists, or 鈥渆ar nose and throat鈥 doctors, and is generally identified following viral infection. But there have been few documented cases of hearing loss associated with COVID-19.

Intensive care unit doctors intubated the in this case study for 30 days. After receiving remdesivir, intravenous steroids and plasma exchange as treatment, his condition improved but he then experienced hearing loss. He had no history of hearing issues. After some treatment with steroids, he experienced partial improvement, but doctors considered the hearing loss to be irreversible. They identified no cause but postulated that it was related to COVID-19.

ABDOMINAL PAIN AND COVID-19

The 33-year-old man at the centre of this case study, , was a non-smoker, 鈥渦sually fit and well,鈥 who showed up to an emergency room in Newcastle, England, three times in the span of a single day complaining of severe abdominal pain initially attributed to gastroenteritis. At the time of his admission, doctors were using guidance from April that did not include abdominal pain as a COVID-19 symptom. He had a fever for a few days and experienced one bout of vomiting. He was treated for possible bacterial pneumonia, but nasal swabs came back negative for COVID-19.

On his third day in hospital, his sputum finally tested positive for the virus and his need for oxygen support increased. Doctors admitted him to the intensive care unit, where he recovered and was released on his ninth day in the hospital. Physicians identified a rare respiratory tract pathogen called Yersinia enterocolitica that contributed to his severe abdominal pain, making him one of the first documented cases of Y. enterocolitica co-infection with COVID-19. The case demonstrated the need for testing saliva and mucus from the respiratory tract when there is suspicion of COVID-19 even when nasal swabs are negative.

BABY BORN WITH TWO MOUTHS

In the most-read non-coronavirus case report of 2020, doctors removed a second mouth from a six-month-old girl in the United States. The rare condition called craniofacial duplication was first reported more than 70 years ago in a two-day-old child. Doctors in both that incident and this 2020 case noted duplication of the mouth and tongue with 鈥渟ynchronous accessory tongue movement.鈥 Physicians first noted the girl鈥檚 second mouth in an ultrasound during the third trimester of her mother鈥檚 pregnancy, but weren鈥檛 sure what it was until she was born.

Here are the remaining most-read case reports from the BMJ Case Reports:

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Correction:

An earlier version of this story incorrectly cited the British Medical Journal instead of the separate journal BMJ Case Reports.