Assessment

HISTORY. Elicit a careful history of the patient's symptoms and pay particular attention to changes that involve the eyes, which are often the earliest signs of MG. These changes include ptosis (eyelid drooping), diplopia (double vision), reduced eye closure, and blurred vision. Ask if the patient has to tilt the head back to see properly. Question the patient about weight loss because of problems with chewing and swallowing. Determine the patient's ability to perform sustained or repetitive movements of the extremities, such as brushing the hair or carrying groceries. Determine if the symptoms are milder in the morning, worsen as the day progresses, and subside after short rest periods. Ask the patient if the head bobs when she or he is tired or if the jaw hangs open.

PHYSICAL EXAMINATION. You may note a "masklike" or "snarling" appearance because of the involvement of the facial muscles. Note if the patient has weak neck muscles that cause difficulty in maintaining head position. Assess the patient's posture and body alignment because the patient may slouch or walk with a slow gait. The patient's voice may fade during conversation. Determine the symmetry of muscle strength and movement. Perform an eye examination to determine visual acuity and eye movement, which are often abnormal. When you auscultate the patient's lungs, you may hear decreased breath sounds resulting from hypoventilation.

The patient who has confirmed MG may develop acute exacerbations, which can occur in two forms: myasthenic or cholinergic crisis. Myasthenic crisis is caused by undermedication and is also characterized by hypoxia (associated with tachycardia and possible elevated blood pressure), absence of the cough and gag reflexes, ptosis, diplopia and mydriasis (large pupils), and a positive response to the medication edrophonium (Tensilon). In comparison, a cholinergic crisis results from excessive anticholinesterase medication and is likely to occur within 45 to 60 minutes after the last drug dose. Side effects of overmedication include diarrhea and abdominal cramping, bradycardia and possible hypotension, a flushed diaphoretic appearance, miosis (small pupils), and increased secretions (saliva, tears, and bronchial secretions). Response to Tensilon is negative, and twitching and "thick tongue" dysphagia may occur.

PSYCHOSOCIAL. The course of MG is unpredictable because of its exacerbations and remissions. Patients live in fear of not being able to breathe adequately. Depression may occur in patients who experience exacerbations and functional limitations in their lifestyles and role responsibilities. Assess the family's support system and ability to deal with chronic disease and any emergency situation that may occur.

Diagnostic Highlights

Test

Normal Result

Abnormality with Condition

Explanation

Anti-acetylcholine receptor antibody (AChr) antibody

Negative

Positive

Reliable for diagnosing autoimmune MG; positive result for anti-AChR antibody (Ab) in 74% of patients; positive in 80% of patients with generalized myasthenia; positive in 50% of those with ocular myasthenia

Acetylcholine receptor antibody test

Negative = 0.03 nmol/L

Positive

Detects presence of antibodies against the acetylcholine receptor in serum; antibody interferes with acetylcholine binding, preventing muscle contraction

Electromyography (EMG)

Normal response to repeated nerve stimulation

Decremental response to repetitive nerve stimulation

Skeletal muscle action potential is tested to determine the response to repeated stimulations

Edrophonium (Tensilon) Test: After administration, there is a marked, temporary improvement of strength; administration of 10 mg of edrophonium IV over 30 sec to determine if blocking cholinesterase improves symptoms temporarily.

648 Myasthenia Gravis

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