Myasthenia gravis: Pharmacologic Rx

Pharmacologic management of myasthenia gravis [1] consists of symptom management with anticholinesterase agents, chronic immunosuppression, and in severe cases, rapid intravenous immunotherapy.

Acetylcholinesterase (ACh) inhibitors are often the first line of treatment for patients with symptomatic weakness. ACh inhibitors prevent the breakdown of acetylcholine that occurs naturally in the neuromuscular junction. As such, ACh inhibitors provide symptomatic relief by increasing the concentration of acetylcholine at the neuromuscular junction but do not treat the underlying condition. For adults, pyridostigmine is usually started at 30 mg TID. For children, the initial dose is 0.5 to 1 mg/kg q4-6h. These doses should be titrated to effect (i.e. increased muscle strength). Side effects include abdominal cramping, diarrhea, increased salivation and bronchial secretions, nausea, sweating, bradycardia, fasciculations, and muscle cramping.

Some patients remain symptomatic despite treatment with an ACh inhibitor, or become symptomatic again after a good but temporary response. In these cases, the underlying condition can be treated with immunosuppressive agents. These include glucocorticoids (i.e., prednisone), azathioprine, mycophenolate mofetil, cyclosporine, and rituximab. The choice of a specific agent is individualized based on patient factors, preferences, and cost.

Patients with a severe exacerbation of symptoms (i.e. myasthenic crisis) or who are preparing for surgery may require more rapid treatment. Plasmapheresis directly removes the pathologic acetylcholine receptor antibodies from circulation. Intravenous Immune globulin (IVIG) is anti-inflammatory and immunomodulatory, but the exact mechanism of action in treating myasthenia gravis is unknown.

Surgical treatment with thymectomy is the best intervention, even for most patients without a thymoma [2].