When the Dx is myasthenia gravis

Author: Shawnna Cunning
Issue: April, 2000 RN magazine

Diagnosing the illness

Treatment

Getting through a crisis

Patient education

Myasthenia gravis is a potentially debilitating disease that carries with it the ever-present risk of a clinical crisis. An awareness of signs and symptoms, coupled with diligent nursing care and medical management, can prevent complications and help patients live full, functional lives.

Five years ago, Diana Paisley, a 30-year-old mother of two, began to notice that her legs were getting weaker, and she had problems focusing when reading and driving.

A neurological exam by her primary care physician showed that Mrs. Paisley had trouble lifting her eyebrows and gazing upward. Her mouth also drooped slightly to the left when she smiled. Her left leg strength was 3/5-she could lift her limb against gravity but not against active resistance. Her right leg was a bit stronger; she could at least move it against moderate resistance.

A series of tests led to a diagnosis of myasthenia gravis (MG), an autoimmune, neuromuscular disorder characterized by fluctuating weakness of the voluntary muscles. Mrs. Paisley was started on drug therapy which, for the most part, has controlled her symptoms.

Not today. Today, for the third time in five years, Mrs. Paisley is admitted to the ICU with severe shortness of breath and dysphagia. She complains of extreme weakness and has a nonproductive cough.

She's having a myasthenic crisis-a sudden, severe relapse of myasthenic symptoms. Infection is a common trigger. In this case, a UTI is the suspected cause.

Myasthenia gravis is the most common primary disorder of neuromuscular transmission. [1] The Myasthenia Gravis Foundation of America estimates that 14 out of every 100,000 people in the United States have MG. The disease affects both women and men, and can occur at any age.

Nurses in many different settings have the opportunity to help MG patients lead lives that are as near to normal as possible--and to help recognize and manage emergencies. To do so, you need to be knowledgeable about the disorder, the treatment options, and the essentials of nursing care.

An insidious disease with disabling effects

In MG, antibodies attack the acetylcholine receptors (AChRs) of the neuromuscular junction, interfering with nerve impulse transmission to the muscles. (See the box on page 27 for more about pathophysiology.) Onset of symptoms is usually gradual, progressing over a period of five to seven years. [2] The severity of weakness and the muscles involved vary from patient to patient, and may vary from hour to hour in the same patient. Weakness tends to worsen with use of the affected muscles and improve with rest.

Ocular motor disturbances--such as ptosis or diplopia--are the most common initial symptoms. In about 15% of cases, MG remains confined to the eye muscles. [2] When it doesn't, early findings may include weakness of the facial and oropharyngeal muscles. A smile resembles a snarl, chewing muscles tire quickly, and swallowing or speaking becomes difficult. Even the vocal cords can become weak and sound nasal after talking.

The disease can also affect muscles in the limbs, neck, shoulders, hands, diaphragm, and abdomen. Patients may have trouble walking, sitting up, or raising their arms above the head. Without treatment, respiratory muscles may become so weak that mechanical ventilation is required.

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Treatment options: Long-term or short

No single treatment works for all patients, so an individualized management plan needs to be created once MG is diagnosed. (For an overview of diagnostic tests, see the box on the facing page.) There are a variety of treatment options.

Cholinesterase inhibitors. Drug therapy with ChE inhibitor drugs is the first-line choice for managing MG. These drugs enhance neuromuscular transmission of impulses by preventing degradation of ACh by the ChE enzyme. They are quite effective at alleviating symptoms; in many cases, MG goes into remission and muscle weakness disappears completely.

Mrs. Paisley has been taking pyridostigmine bromide (Mestinon), one of the most commonly used ChE inhibitor drugs. Another is neostigmine (Prostigmin). Dosage varies greatly with ChE inhibitors--both over time and from patient to patient.

These medications can cause a range of adverse reactions. Muscarinic side effects include nausea, vomiting, diarrhea, abdominal cramps, increased salivation and bronchial secretions, and diaphoresis. Nicotinic side effects include muscle cramps, fasciculation, and weakness.

Immunosuppressive drugs. For patients who don't respond to ChE inhibitors, long-term therapy with corticosteroids--which have an immunosuppressive effect--may be an option. The drug of choice is prednisone, which produces marked remission in 70% - 80% of cases. [1]

The goal of therapy is to prevent or minimize the body's attack on its own ACh receptor sites, while maintaining enough immune function to fight infection. Thus, there is a narrow therapeutic range in terms of dosing. The dosage of prednisone is gradually adjusted to find the lowest possible therapeutic dose.

Immunosuppressive medications other than steroids may be used to treat MG, including azathioprine (Imuran), cyclosporine (Sandimmune), and cyclophosphamide (Cytoxan).

Thymectomy. About 80% of patients with myasthenia gravis have hyperplasia of the thymus and 15% have thymomas. [1] Excision of the thymus reduces symptoms of MG in many of these patients. It is complex surgery, though, and patients with MG are at high risk for complications from anesthesia.

Plasma exchange. Plasmapheresis, which removes the destructive AChR antibodies from the patient's plasma, is used to stabilize a patient in myasthenic crisis or as a short-term, preop treatment for a patient under going thymectomy. The length of a treatment series varies by patient. Most patients have improved muscle strength within a day or two of treatment, but the effect lasts only weeks or months. [3]

Intravenous immune globulin. Another treatment option is the administration of IVIG, which is thought to reduce the function or production of AChR antibodies. But, again, any improvement in symptoms is only temporary. [3]

Getting patients through a crisis

As with Mrs. Paisley, even patients whose disease is being managed successfully may suddenly find themselves in a life-threatening situation. Since respiratory failure can develop within minutes once MG starts to affect the breathing muscles, patients having an acute exacerbation of symptoms must be closely monitored.

Assess respiratory rate and effort, oxygen saturation level, ABG values, and forced vital capacity (FVC). Depending on your findings, the physician may decide to have the patient intubated and put on a ventilator. As motor strength and respiratory function improve--generally within 48 hours--the patient can be weaned from the machine.

Determine exactly which muscle groups are affected by weakness. Establish baseline muscle strength on each side of the body--the weakness seen with MG is usually not symmetrical--and reassess that strength at least every half hour.

To prevent muscle atrophy, have the patient do active range-of-motion exercises; if the patient is too weak, perform passive ROM. Monitor exertion levels, and cluster nursing activities to avoid fatiguing the patient. For example, bathe her and do ROM in the same session. If possible, ADLs should be performed after the patient has had a night's sleep, when she is strongest. Throughout the day, provide rest periods between activities.

If the patient is at risk for aspiration because of weak swallowing muscles or a poor gag reflex, closely monitor eating and swallowing patterns. Position the patient on her side to drain pulmonary secretions, and regularly auscultate for breath sounds. Use chest physiotherapy, coughing exercises, and frequent suctioning to help keep the airway open and prevent pneumonia.

If the cause of a myasthenic crisis can be determined, it needs to be addressed aggressively. Mrs. Paisley's doctor, for example, orders trimethoprim-sulfamethoxazole (Bactrim) to treat her UTI. Other clinical conditions that can trigger a myasthenic crisis, besides infection, include fever and metabolic disorders such as hypokalemia [4]

Drugs that diminish transmission across the neuromuscular junction can also precipitate a crisis. Examples include aminoglycoside antibiotics, local anesthetics, antiarrhythmics, morphine, beta-blockers, calcium channel blockers, and penicillamine (Cuprimine).

Observe patients for physical changes after any new drug is given. Also monitor for adverse reactions to medications they have been taking for a while--namely, ChE inhibitors. An overdose could lead to a cholinergic crisis, in which patients experience severe cholinergic side effects, including profound muscle weakness that may lead to respiratory failure.

It may be hard to differentiate a cholinergic crisis from a myasthenic one. The Tension test (discussed in the box on page 29) can help: Improvement in muscle strength with administration of this drug suggests a myasthenic crisis. No improvement, or further deterioration, suggests a cholinergic crisis. With the latter, the patient will be given atropine, the antidote for an anticholinesterase overdose. See that this drug is kept at the bedside of any MG patient on ChE inhibitor therapy.

Even in cases of myasthenic crisis, ChE inhibitor drugs should be withheld until the patient's condition stabilizes. Before leaving the hospital, the patient's drug regimen will need to be reevaluated and adjusted and her response to the new dosage monitored.

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Teaching improves disease management

Whether newly diagnosed, or just discharged after a crisis, patients should be instructed to take their medication as prescribed, and to take it early enough before eating or engaging in activities to obtain maximum relief when it's needed most. For example, patients on pyridostigmine who have trouble chewing or swallowing should take the drug one to two hours before meals. [2,5]

Teach patients about potential side effects of their drug regimen. In addition, be sure to review the factors that can exacerbate symptoms of MG, including certain drugs, emotional stress, infection, temperature extremes, menstruation, and extensive exposure to ultraviolet light.

Advise patients to wear a medical alert bracelet that identifies them as having MG and to carry a card that has information regarding their medications and primary care physician. Instruct them to call the doctor if weakness develops or facial or upper eyelid drooping occurs, as it could herald an exacerbation of symptoms.

Suggest to patients that they wear sensible shoes to combat muscle fatigue and potential loss of balance. Encourage them to eat regular, balanced meals to prevent fatigue from lack of protein.

The quality of life of a patient with myasthenia gravis can be dramatically improved with proper education and medical management. Nurses, using their assessment and teaching skills, can be a vital link in the continuum of care for patients with MG.

SHAWNNA CUNNING is a former program coordinator for the Chicago Institute of Neurosurgery and Neuroresearch at Riverside Medical Center, Kankakee, Ill. She is currently a clinical nurse specialist in cardiology at Riverside Medical Center.

REFERENCES

(1.) Hickey, J. (1997). Selective degenerative diseases of the nervous system. In The clinical practice of neurological and neurosurgical nursing (4th ed.). (pp. 678 - 684). Philadelphia: Lippincott.

(2.) Keesey, J. C., & Sonshine, R. "A practical guide to myasthenia gravis." www.myasthenia.org/information/practical.htm (4 Jan. 2000).

(3.) Howard, J. F. (1997). "Myasthenia gravis: A summary." http://www.med.unc.edu/mgfa/mgf-sum.htm (4 Jan. 2000).

(4.) Pourmand, R., (1995). Recognizing and managing myasthenic crisis. Emerg. Med. 27(9), 74.

(5.) Becker, A, Grohar-Murray, M. E., et al. (1998). Self-care actions to manage fatigue among myasthenia gravis patients. J. Neurosci. Nurs., 30(3), 191.

KEY WORDS

* myasthenia gravis

* myasthenic crisis

* cholinesterase inhibitors

* immunosuppressive Therapy

* thymectomy

* plasmapheresis

* intravenous immune globulin

* cholinergic crisis

Diagnosing myasthenia gravis

Since muscle fatigue and other symptoms of MG are nonspecific, nurses and other clinicians need to maintain a high index of suspicion for the disease. Several tests can help confirm or rule out the diagnosis.

One of the most common is the edrophonium chloride (Tensilon) test. If the patient's strength improves for at least live to 10 minutes after IV administration of this drug, the test is considered positive. Some patients who don't respond to Tensilon may respond to TM administration of neostigmine (Prostigmin), which has a longer duration of action.

Another diagnostic option is serum testing for antibodies to acetylcholine receptors. In general, an elevated AChR-antibody level in conjunction with clinical symptoms confirms the diagnosis. However, normal antibody concentrations do not necessarily exclude a diagnosis of MG.

Also, elevated AChR-antibody levels may be caused by factors unrelated to MG, such as general anesthesia, muscle relaxants, lupus erythematosus, inflammatory neuropathy, and amyotrophic lateral sclerosis. Levels are also high in rheumatoid arthritis patients who take penicillamine and in healthy relatives of patients with MG.

Another test, single fiber electromyography, can detect delays or failure of neuromuscular transmission in pairs of muscle fibers. It's 99% sensitive in diagnosing MG, but it's also less readily available than either the Tensilon test or serum testing. [1]

REFERENCE

(1.) Hickey. J. (1997). Selective degenerative diseases of the nervous system. In The clinical practice of neurological and neurosurgical nursing (4th ed.) (pp. 678 - 684). Philadelphia: Lippincott.

Nursing diagnoses for patients with MG

* Motor weakness related to impaired mobility

* Ineffective breathing pattern related to weakness of respiratory muscles

* High risk for aspiration related to weakness of swallowing muscles

* Knowledge deficit related to hospitalization/disease process

* Anxiety related to body changes and loss of control

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