AANP Family Nurse Practitioner (FNP) Certification ExamAssessmentMedium
A 42-year-old female presents with a 6-month history of fatigue, generalized muscle weakness that worsens with activity and improves with rest, and fluctuating ptosis and diplopia, particularly in the evenings. On examination, she has symmetric proximal muscle weakness. Which of the following is the most appropriate initial diagnostic test?
- ATensilon (edrophonium) test
- BThyroid function tests
- CElectromyography (EMG) with nerve conduction studies (NCS)
- DAcetylcholine receptor (AChR) antibody test
Show answer & explanationAnswer & explanation
Correct answer: D. Acetylcholine receptor (AChR) antibody test
The patient's fluctuating muscle weakness, worsening with activity and improving with rest, and specific ocular symptoms (ptosis, diplopia) are highly characteristic of myasthenia gravis. The most appropriate initial diagnostic test to confirm this autoimmune disorder is the acetylcholine receptor (AChR) antibody test, which is highly specific and sensitive.
Why the other options are wrong
- A. The Tensilon test (edrophonium) is a pharmacological test that can provide rapid, temporary improvement in symptoms, but it carries risks and is often used after antibody testing or if results are unclear.
- B. Thyroid dysfunction can cause muscle weakness but doesn't explain the characteristic fluctuating, activity-dependent pattern or the specific ocular symptoms of myasthenia gravis.
- C. EMG with NCS can show a decremental response to repetitive nerve stimulation, which supports the diagnosis, but the antibody test is usually performed first due to its high specificity.
Myasthenia Gravis Diagnosis
The process of identifying an autoimmune neuromuscular disorder characterized by fluctuating muscle weakness and fatigue.
- Weakness worsens with activity, improves with rest.
- Often involves ocular (ptosis, diplopia) and bulbar muscles.
- Diagnosis confirmed by AChR antibody test.
Memory trick: Myasthenia: 'M'uscle 'G'et 'A'ntibodies.