Dog Owner's Home Veterinary Handbook.pdf - Mr. Walnuts

374 •DOG OWNER’S HOME VETERINARY HANDBOOK
Dachshunds, and Scottish Terriers, often occurring at 1 to 4 years of age or 9 to
13 years of age. Acquired myasthenia gravis is an immune-mediated disease in
which auto-antibodies are directed at and destroy the acetylcholine receptors.
Hypothyroidism can occur at the same time as autoimmune myasthenia
gravis. Occasionally, myasthenia gravis is related to a tumor of the thymus
gland, but this is rare.
The diagnosis of myasthenia gravis is based on neurological examination.
One test involves injecting a drug called edrophonium chloride. This drug
blocks the enzyme that breaks down acetylcholine, resulting in higher concentrations
of this neurotransmitter at the receptor sites. The test is positive if
muscle strength improves after the injection. A serologic test for diagnosing
autoimmune myasthenia gravis is available.
Treatment: Drugs are available that increase the concentration of acetylcholine
at receptor sites, thereby reversing muscle weakness. These drugs can
be given as a syrup or by injection. The dose varies according to the dog’s
activity and stress levels. Close veterinary monitoring is required. Drugs to
counter immune responses may also be helpful.
Megaesophagus is treated as described on page 258. Thymus gland tumors
are removed surgically. Hypothyroidism responds to thyroid replacement
therapy (see page 142). With appropriate treatment, the outlook for complete
recovery and the return of normal swallowing is good.
HYPOKALEMIA (LOW SERUM POTASSIUM)
Hypokalemia, a condition in which the dog has low serum potassium, is a
metabolic cause of generalized muscle weakness. Loss of potassium occurs with
severe vomiting. It also occurs with the long-term use of diuretics that cause
the kidneys to excrete potassium, such as Lasix (furosemide). Other causes of
hypokalemia include bloat, diabetic ketoacidosis, and Cushing’s syndrome.
Treatment: The diagnosis is made by measuring serum potassium levels.
Weakness disappears as potassium is replaced and the underlying cause is corrected.
Close veterinary supervision is required until normal levels are restored.
Spinal Cord Diseases
Injuries and diseases of the spinal cord generally produce weakness and paralysis
in one or more limbs and/or the tail. Spinal cord diseases do not cause
seizures, nor do they produce changes in personality or behavior. This sets
them apart from brain diseases. However, injuries to peripheral nerves may be
difficult to distinguish from spinal cord injuries.