What is Malignant Hyperthermia?
Malignant hyperthermia is a grim condition in dogs that can lead to muscular diseases, and is more prominent in Greyhounds. It is an inherited mutation of the dominant genes that results in serious physical reactions due to certain triggers.
These can range from a reaction to different medications, gaseous anesthetics, caffeine, hops, and any activity level that is too demanding, or when the dog is stressed out; because of this last reason it is also nicknamed “canine stress syndrome”.
Depending on the seriousness of malignant hyperthermia affecting your dog, the outlook ranges from fair to guarded, though with proper care and treatment, he can be expected to return to a level of living that is comparable to before malignant hyperthermia affected him.
Malignant Hyperthermia, though uncommon, is a life-threatening condition that is due to a genetic mutation, triggered by different sources. It can have a very sudden onset and can escalate quickly, and proving fatal if not caught and treated promptly.
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Symptoms of Malignant Hyperthermia in Dogs
Symptoms can develop quickly and these include:
- The first sign is usually a sudden and dramatic increase of carbon dioxide
- Fever that elevates quickly and stays elevated up to 113F (45C)
- Rapid heartbeat (tachycardia)
- Rapid breathing (tachypnea)
- Cyanosis (the discoloration of skin due to low oxygen levels)
- Rigid muscles
- Possible seizures
- Changes in blood pressure
- Fluid in the lungs
- Difficulty to form blood clots
- Kidney failure
The dogs that are affected by malignant hyperthermia have a predisposition to the condition because of a genetic mutation they inherited. The breeds more prone to malignant hyperthermia are:
- Bichon Frises
- Border Collies
- Doberman Pinschers
- German Shepherd/Doberman Pinscher mixes
- Golden Retrievers
- Greyhounds (this is the most commonly affected breed)
- Labrador Retrievers
- Saint Bernards
- Springer Spaniels
Causes of Malignant Hyperthermia in Dogs
The biggest cause of malignant hyperthermia is from drugs during anesthesia. The drugs that are unsafe for malignant hyperthermia susceptible dogs are:
- Inhaled general anesthetics
- Halothane (because of its extreme ability to trigger malignant hyperthermia, this drug is not used in western countries anymore)
- Succinylcholine (because of its extreme ability to trigger malignant hyperthermia, this drug has become restricted over time by international anesthesia societies)
Additional causes for malignant hyperthermia include:
Diagnosis of Malignant Hyperthermia in Dogs
Malignant hyperthermia is a difficult mutation to diagnose and tests that are minimally invasive and are helping to highlight the susceptibility a dog may have are being created.
The best way to diagnose malignant hyperthermia is to conduct a muscle biopsy, through means of a procedure called the In Vitro Contracture Test (IVCT) though this can give both false positive, and false negative results equally. The problem with this method is that the dog must be anesthetized for the biopsy to be collected, and most veterinarians will not put a dog that is suspected for malignant hyperthermia under anesthesia because of the risk associated with the drugs used.
Another means of diagnosis is through a DNA analysis. This will be done using a blood sample collected from your dog and then sent to a diagnostic laboratory where it will be tested for the RYR1 genetic mutation.
As malignant hyperthermia can have a sudden and unexpected onset in undiagnosed dogs, the clinical tests used to diagnose the condition will be rendered useless. A dog will only be officially diagnosed as malignant hyperthermia susceptible if one of the 31 known mutations are detected in the RYR1 screen. Other tests used in helping to diagnose are:
- Blood bicarbonate of EDTA blood
- Blood pH on EDTA blood
- Blood pressure test
- Serum chemistry
- Urine sedimentation
- Halothane-succinylcholine challenge exposure test (this test can result in death of a malignant hyperthermia positive dog, and because of this, is not a test that veterinarians like to use)
- Caffeine induced contraction test on muscle biopsies
- RBC fragility test
Treatment of Malignant Hyperthermia in Dogs
For dogs that are having an attack of malignant hyperthermia, there is unfortunately only one treatment option. It requires an injection of a muscle relaxer called Dantrolene done intravenously, while being kept on fluids through the IV as well. The dog needs to be instantly taken off of the anesthetics, while having his temperature brought back to a normal level and monitoring his breathing. Malignant hyperthermia, even if treated properly and quickly can still sometimes be deadly.
Recovery of Malignant Hyperthermia in Dogs
Recovery from an attack of malignant hyperthermia stands a better chance when it is caught early and the treatment is started immediately. The only way to manage malignant hyperthermia, as there is no cure for it, is to have your dog monitored non-stop before, during, and after any procedure requiring an anesthetic, and employing an anesthetic that will not trigger the disease.
Malignant Hyperthermia Questions and Advice from Veterinary Professionals
After a dozen different vets my heeler mix was finally diagnosed mh instead of fuo he gets bad almost weekly usually from over exertion he's only ten months and extremely hyper. I constantly struggle between attempts to let him blow off steam and him destroying everything because he's looking for an outlet for his excess energy and anxiety. Is there any medication I can put him on herbal or otherwise to help with that? Also when he relapses I have been giving him 10mg prednisone which seems to help as well as feeding him ice and chicken. Which is the only thing he will eat or keep down. The last vet said the prednisone is doing nothing but I swear it helps. Am I just fooling myself about its effectiveness? He also seems to be more prone to relapses if he doesn't eat every few hours almost. Symptoms bar isn't working he has shortness of breath convulsions extreme fever avg 106.5
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I saw Malignant Hyperthermia was prone in Border Collies, what other genetic diseases can they get? I want to know what my dog is at risk for so we can prepare for other possible problems.
Whilst Border Collies may be predisposed or may have a genetic trait (like MDR1 which is why ivermectin isn’t recommended in this breed), you shouldn’t get yourself too tied up worrying about possible problems which Xayah may develop; if you are wanting to get a better picture of Xayah from a genetic perspective it may be worth having a DNA test performed which will give you an indication of Xayah’s probability of being affected by certain traits.
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