A nurse is assessing a 45-year-old patient with suspected myasthenia gravis. Which assessment finding would be most indicative of this condition?
1Muscle rigidity and bradykinesia that improves with movement
2Fasciculations and muscle atrophy in the hands and feet
3Tremor at rest that decreases with purposeful movement
4Ptosis and diplopia that worsen with sustained activity✓ 정답
해설
Ptosis and diplopia worsening with sustained activity are characteristic ocular signs of myasthenia gravis, reflecting fatigable weakness. Other options describe Parkinson's (rigidity/bradykinesia), ALS (fasciculations/atrophy), or Parkinson's tremor (resting tremor).
Clinical Judgment
This question assesses the ability to identify the most specific physical examination finding for Myasthenia Gravis. The key is understanding the nature of the disease—"muscle weakness that worsens with activity and improves with rest"—and selecting the objective assessment method that most clearly demonstrates this. Option 4, "ptosis that worsens with sustained upward gaze," is a specific finding that directly demonstrates the core pathology of muscle fatigability, which a nurse can observe by watching the patient's facial expressions and eye movements during conversation. The other options are more characteristic of other neurological conditions, such as Parkinson's disease or Guillain-Barré syndrome.
Memory Tip:
The hallmark of Myasthenia Gravis is Fatigable Weakness. Remember the mnemonic: "Myasthenia Gravis gets Grave with Gravity." Muscles that work against gravity, such as lifting the eyelids or arms, become particularly weak.
KR vs US:
In Korea, neurologists primarily perform the Tensilon (edrophonium) test or antibody tests to diagnose Myasthenia Gravis. In the US NGN/CJMM, the nurse's initial assessment and clinical judgment are emphasized more as the first step in the diagnostic process. As in this question, the ability to recognize specific signs that a nurse can detect during history-taking and physical examination is very important.
Clinical Assessment for Suspected Myasthenia Gravis
When evaluating a patient for myasthenia gravis (MG), focus on eliciting fatigable weakness. The ocular muscles are affected in over 50% of initial presentations. Key examination techniques include:
Sustained Upgaze Test: Ask the patient to maintain upward gaze for 30-60 seconds. Progressive ptosis or diplopia strongly supports MG.
Ice Pack Test: Apply an ice pack to the closed eyelid for 2 minutes. Improvement in ptosis is a sensitive bedside sign due to enhanced neuromuscular transmission at cooler temperatures.
Edrophonium (Tensilon) Test: Historically used, a short-acting acetylcholinesterase inhibitor is administered intravenously with transient improvement in muscle strength. This is rarely performed now due to cardiac risks; have atropine ready as an antidote.
Diagnostic Workup
Confirmatory testing includes:
Serologic Testing: Acetylcholine receptor (AChR) binding antibodies are positive in approximately 85% of generalized MG. If negative, test for muscle-specific kinase (MuSK) antibodies.
Electrodiagnostic Studies: Repetitive nerve stimulation shows a decremental response (>10% decrease in compound muscle action potential amplitude). Single-fiber electromyography is the most sensitive test.
Imaging: CT or MRI of the chest is mandatory to evaluate for thymoma, present in 10-15% of MG patients.
Nursing Considerations
Nurses must monitor for myasthenic crisis (respiratory muscle weakness) versus cholinergic crisis (excessive anticholinesterase medication). Both present with respiratory distress, but cholinergic crisis includes excessive salivation, lacrimation, diarrhea, and fasciculations. Schedule activities and medications to maximize strength during meals and self-care. Administer pyridostigmine 30-60 minutes before meals to improve swallowing and prevent aspiration.
Fatigable Weakness — Muscle weakness that worsens with sustained or repeated activity and improves with rest, the hallmark clinical feature of myasthenia gravis.
Ptosis — Drooping of the upper eyelid due to weakness of the levator palpebrae superioris muscle, commonly seen in myasthenia gravis.
Diplopia — Double vision resulting from weakness of extraocular muscles, a frequent initial symptom of myasthenia gravis.
Acetylcholine Receptor Antibodies — Autoantibodies that attack and destroy postsynaptic nicotinic acetylcholine receptors at the neuromuscular junction, causing impaired transmission in myasthenia gravis.