Myasthenia gravis in dogs is a neuromuscular condition marked by abnormalities in the relaying of signals from the nerves to varied muscles. This can then hamper contraction of the muscles leading to increased weakness in affected dogs.
Causes of myasthenia gravis in dogs
- Myasthenia gravis in dogs is often familial, i.e., it tends to be passed down generations, or congenital, i.e., it is present from birth. The disease is marked by an autosomal recessive type of inheritance. It usually becomes easily noticeable when the affected dogs are 5 to 8 weeks old. Some of the breeds that are carriers of the genetic defect include English springer spaniels, Jack Russell terriers, miniature smooth-haired dachshunds, and smooth fox terriers.
- It is also possible for myasthenia gravis to not be an inherited disease, but be an acquired one which develops later in their lives. However, as is the case with most autoimmune disorders, myasthenia gravis in dogs can only occur if associated genetic defects are already present. The disease can get triggered due to varied factors such as infection, environment, and hormonal imbalances. It can commence in two age groups, i.e., when the dogs are between 1 to 4 years old or when they are 9 to 14 years old. Female dogs in the younger age group are somewhat more vulnerable than male dogs. This anomaly is not observed in the older age group. The acquired form of myasthenia gravis typically affects the Great Dane and Newfoundland species. It can also be found in other dog breeds such as German shepherds, golden retrievers, Labrador retrievers, Scottish terriers, dachshunds, and Akitas.
All types of dogs as well as both the genders are vulnerable to developing myasthenia gravis. It may be noted that dogs that experience the acquired form of the disease generally have a good prognosis as long as the treatment is timely and correct.
The below listed risk factors can increase the vulnerability of dogs to developing myasthenia gravis:
- An underlying cancer or tumor, especially tumor of the thymus gland
- The related genetic defects
- Non-sterilization in female dogs
- An underlying case of myasthenia gravis can deteriorate due to vaccination.
Symptoms
Myasthenia gravis in dogs refers to impulse transmission problems between the muscles and nerves and is marked by increased fatigue and weakness of the muscles.
The acquired type may come with a variety of signs and symptoms such as localized problems of the throat and esophageal muscles, mild overall muscular collapse, and defects of the muscles near the eyes. Affected dogs may also regurgitate, but this abnormality is different from vomiting.
It is imperative for pet owners to test for the presence of myasthenia gravis if their pet dog exhibits any abnormal symptoms such loss of or deficits in usual reflexes, esophageal enlargement over some time, or the development of an anomalous mass in the front middle section of the dog’s chest.
Some of the visible signs and symptoms of myasthenia gravis are as follows:
- Weakness associated with exercising, but normal appearance when resting.
- Changes in the voice
- Weakness that progressively worsens
- Acute collapse
- Even mild exercising can cause cramps and fatigue
- There is no abnormal loss of muscle mass
- Sleeping with open eyes
- Aspiration pneumonia along with breathing problems
- Difficulty in swallowing; affected dog may make many attempts to swallow.
- Increased drooling.
- Nervous system abnormalities include:
- The gag reflex may be absent or very poor
- Blink reflex is also absent or lowered
- Spinal reflexes are the same, but it is prone to easy tiredness
Diagnosis
- A vet will go for a complete neurologic and physical examination, study the medical history of the dog, and recommend specific tests in a lab before diagnosing myasthenia gravis in dogs. The vet will also check for other conditions with similar symptoms, like tick paralysis, and rule them out before arriving at a definite conclusion.
- A few diagnostic tests that a vet may go for include thyroid function tests, urinalysis, a complete blood test, and imaging tests like an ultrasound of the chest to check for tumors or an x-ray of the esophagus to verify any enlargement. Biopsy is performed if a tumor is found to verify if it is malignant.
Treatment
- Dogs with myasthenia gravis need to be hospitalized and relevant dosages of varied drugs are given as treatment.
- Tumors need to be removed via surgery.
- Aspiration pneumonia may need varied therapies such as intensive antibiotic therapy, oxygen therapy, supportive care, and intravenous fluid therapy.
- Feeding and swallowing problems are overcome with the use of a feeding tube. Affected dogs are given a high calorie diet to provide sufficient nutrition to the dog.
After treatment is over, muscle strength will return to normalcy in some weeks. Pet owners need to go for follow-up visits every few weeks as suggested by the vet. The disease cannot be prevented. Early detection and treatment is the only way to get a good prognosis.