Ginger, a three-month old Cavalier King Charles Spaniel puppy who had a very painful mouth

Ginger had been a completely normal puppy, playing enthusiastically, and eating hungrily. Over a twelve-hour period, everything changed. She became dull and quiet, no longer wanting to play with Finn, and she had no interest in food at all. When Finn reached out his hand to pet her head and reassure her, she backed away, and yelped as if she was in pain.

Ginger was brought in to see me at once and it was obvious that she had a serious problem. She was painful all around her head, and she would not let me open her mouth at all. Was there something stuck inside her mouth? After my morning appointments were finished, I gave her a general anaesthetic, but to my surprise, even then I was unable to open her mouth more than one inch wide. I took x-ray pictures of her skull to see if there was some type of abnormality or injury. The bones and joints of her skull and neck looked completely normal in the x-rays. There were a few different possible causes of Ginger’s severe pain, but initially there was no easy way of finding out precisely what was going on. I sent her home with strong pain relief, and instructions to offer her tasty, moist food that she would find easy to eat without chewing.

Ginger came back in to see me two days later. She had developed the first of many complications in her illness. Her mouth seemed more comfortable, and she was eating, but she had a severe gastrointestinal upset. She had to stop all medication to allow her digestive system to return to normal. Of course, the lack of pain relief then meant that she started to yelp in pain again, and for a few days it was a case of juggling her medications to try to reach the right balance of effective drugs without the risk of digestive upsets.

Meanwhile, I was doing some background research about what could be causing her problem. I had sent blood samples to the laboratory for analysis, but as with the x-rays, everything was normal. I telephoned the University Veterinary Faculty to discuss the case, wondering if specialised tests such as “electromyography” (EMG) might be available. These tests are common in the human world, using electrical recording apparatus to assess the function of different muscle groups. They are rarely used in the veterinary world, but centres of excellence such as UCD are the most likely places to be carrying out such work.

As it happened, it was not going to be easy to organise such investigations in the immediate future, but the staff at UCD were exceptionally helpful. Somebody had come across interesting news from California. A specialised veterinary neuromuscular centre in San Diego had just published a report about eleven Cavalier King Charles Spaniel puppies that had developed severe jaw pain, just like Ginger. Full investigations – including electrical tests and even muscle biopsies – had proven that the puppies were suffering from a condition known as Masticatory Muscle Myositis. This rare condition happens when the body develops an immune reaction to its own muscle fibres. The muscle fibres around the jaws are “rejected”, in the same way as a new kidney can be rejected after a kidney transplant. As a result, the muscles become swollen and painful. Once the condition is diagnosed, it can be effectively treated by giving drugs to suppress the immune system.

I sent an email to the San Diego laboratory at once, explaining Ginger’s background. Their reply was encouraging. They had continued to see small numbers of Cavalier puppies with this problem, and they had developed a special antibody test that could be used to confirm the diagnosis without the need for complicated workups or muscle biopsies. If I could send them a small blood sample from Ginger, they would be able to confirm the diagnosis. I did this at once.

At this stage, to make things even worse, Ginger managed to aggravate a local cat, who swiped her across the head in anger, causing a nasty cat scratch to her right eye. She had to be rushed to a specialist eye surgeon for emergency surgery. She recovered well, but Ginger was not having an easy life. Poor Finn wondered if he was ever going to have a normal puppy as a playmate. Two weeks later, the results from the Californian blood tests arrived, and they confirmed the diagnosis. Ginger was definitely suffering from Masticatory Muscle Myositis. I started her onto a high level of immunosuppressive drugs to stop her body from rejecting her own jaw muscles. She responded well immediately, and she has been more-or-less pain-free since the drugs were started.

Ginger still has problems: her head muscles have been scarred, and she is unable to open her mouth properly. Her tongue lolls out of her mouth in a strange way, and she is smaller than other puppies of her age. Her illness has ensured that she was wriggled her way into the hearts of everyone in her household. Ginger plays enthusiastically now, and she will go on to have a normal life, thanks to the help of modern medicine.


  • Rare illnesses can affect pets, just like humans
  • A full diagnosis is essential in order to give the best possible treatment
  • Some puppies just seem to be prone to problems!

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Please note that I am unable to answer veterinary questions in comments. If you have questions or concerns about your pet's health it is always better to contact your vet.

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