Prevention and treatment of aspiration pneumonia is an essential consideration in animals with acquired MG. Frequent turning of recumbent animals, antibiotic therapy, nebulization and coupage are examples of treatment considerations for aspiration pneumonia.
Maintenance of adequate hydration is essential in animals with acquired MG. Intravenous fluid therapy may be necessary in animals that regurgitate liquids.
Special feeding procedures (e.g., feeding food and water from elevated feed bowls or holding an animal in a vertical position for AT LEAST 20 minutes after feeding), placement of a gastrotomy tube, and in some cases parenteral nutrition, must be considered. Construction of special chairs (“Bailey chair”) to aid in upright feeding can be invaluable.
Intensive care and ventilatory support may be required in animals with severe aspiration pneumonia or severe generalized weakness.
Modification of gastrointestinal tract function:
Management of dysphagia and megaesophagus, with associated complications of aspiration pneumonia, regurgitation and esophagitis, is an essential consideration. Drugs that may improve esophageal motility (e.g., metoclopramide), increase lower esophageal sphincter tone (e.g., cisapride), or increase the pH of gastrointestinal contents (e.g., cimetidine or ranitidine) should be considered.
Specific therapy for acquired MG is based on the severity of the disease in a specific animal. To facilitate treatment decisions, a classification system that addresses the heterogeneous and variable clinical signs of acquired MG has been introduced for use in dogs and cats:
Group 1: Mild or focal MG
Group 2: Moderate generalized MG
Group 3: Severe generalized or acute fulminating MG.
1) Anticholinesterase agents
Anticholinesterase agents, that act to enhance neuromuscular transmission by prolonging the action of acetylcholine at the neuromuscular junction, are used in all the above patient groups. Dosage must be adjusted for each dog or cat depending on individual tolerance of adverse effects and response to treatment. Drugs available include pyridostigmine bromide (Mestinon®, 1-3 mg/kg, orally BID or TID) and neostigmine bromide (Prostigmin®, 2 mg/kg/d, orally in divided doses to effect). Pyridostigmine bromide is available in four dosage forms syrup, conventional tablets, slow release tablets and injectable forms.
2) Immunosuppressive therapy
Should an optimal response to therapy not be achieved with supportive care and anticholinesterase drugs, immunosuppressive drugs may be used. Use of immunosuppressive drugs is controversial, particularly as a “first line” treatment, due to the high incidence of aspiration pneumonia (particularly in dogs) and the potential for glucocorticoids to exacerbate muscle weakness. Glucocorticoids. Low dose prednisone therapy (0.5 mg/kg every other day) has been recommended in mildly (Group 1) and moderately (Group 2) affected animals.
Contraindications for glucocorticoid therapy include ongoing infections or aspiration pneumonia, diabetes mellitus, severe obesity, uncontrolled hypertension, and gastrointestinal ulcerations.
Other immunosuppressive agents (e.g., azathioprine, cyclosporine, cyclophosphamide, mycophenolate mofetil) may be recommended for animals in Groups 1 and 2 where use of glucocorticoids is contraindicated, or should adverse effects of glucocorticoids become difficult to manage.
Should a concurrent thymic mass or other neoplasia be present, then surgical removal, with or without radiation therapy, should be considered. As a majority of dogs with thymoma and acquired MG also have megaesophagus and aspiration pneumonia, and because mortality rate after thymectomy in these dogs is high, it is recommended to delay thymectomy until clinical signs of MG are controlled by means of medical management.
Treatment of Acute Fulminating Myasthenia Gravis:
Management of severe generalized acquired MG (Group 3) is difficult. Affected animals should be managed in an intensive care unit. Anticholinesterase therapy and ventilatory support provide the basis for therapy. Ventilatory support usually is required due to weakness of intercostal muscles and diaphragm, or due to concurrent pulmonary infection (often resulting from aspiration pneumonia). Plasmapheresis and intravenous immunoglobulin have been used to treat people with acute fulminating MG.
Monitoring the Response to Treatment:
In the absence of immunosuppression, determination of serial AchR antibody titers may aid in determination of both disease status and duration of treatment.