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Author [[PageAuthor::Ahmed Zaghw, M.D. [1]]]
Exam Type USMLE Step 2 CK
Main Category
Sub Category Head and Neck, Musculoskeletal/Rheumatology
Prompt A 45 year old female comes to the clinic with a weakness and not feeling well. She has been in bad mood since he lost her two sons in car accident two months ago. Since then, she has been worrying alot about of issues in her life. She has sought a psychiatric consultation for the frequent nightmares and panic attacks. She also noticed that he has difficulty raising his right eyelid for the last 6 weeks. His medical history is significant for a rheumatoid arthritis has failed to respond to DMARDs for the last 3 years. she drinks a couple beers at weekends. She does not smoke nor take illicit drugs. Her medications are Etanercept, analgesics and Fluxetine. The physical examination shows a ptosis of right eye lid, however the extraocular muscles movement are intact. The full neurological examination does not reveal any abnormality. What would be the best next step in management?
Answer A Tensilon test
Answer A Explanation Correct.- The edrophonium (Tensilon) is the first bed side test to be performed is such a case. This test should be used only in those patients with obvious ptosis or ophthalmoparesis, in whom improvement after infusion of the drug can easily be observed.
Answer B Antibodies to the MUscle specific tyrosine Kinase receptor(MuSK)
Answer B Explanation Incorrect.'-MuSK antibodies are generally not present in those with well-established ocular myasthenia gravis, but they have been detected in a few cases (Arch Neurol. 2005;62(6):1002.). Although nearly half of patients with AChR-Ab negative myasthenia gravis will have MuSK antibodies, those with AChR-Ab positive myasthenia do not have antibodies to MuSK in most studies to date (Ann Neurol. 2004;55(4):580, Neurology. 2003;60(12):1978.)
Answer C Acetylcholine receptor antibodies
Answer C Explanation Incorrect.'- An immunologic assay to detect the presence of circulating acetylcholine receptor antibodies (AChR-Ab) is the first step in the laboratory confirmation of myasthenia.There are three AChR-Ab assays: binding, blocking, and modulating. The test has high specificity, that is why (AChR-Ab) should be performed on all patients.The binding type antibodies is 80-90% of patients with generalized disease, provides the laboratory confirmation of myasthenia gravis(Ann N Y Acad Sci. 1987;505:526).
Answer D Repetitive nerve stimulation test
Answer D Explanation Incorrect.- Electrophysiologic tests usually allow confirmation of the diagnosis in patients who have seronegative myasthenia gravis.Repetitive nerve stimulation (RNS) studies and single-fiber electromyography (SFEMG) have a diagnostic sensitivity in generalized myasthenia of about 75 % and 95 % respectively.
Answer E Chest and neck CT
Answer E Explanation Incorrect.- The role of Chest and neck CT in Myasthenia gravis is to evaluate a thymoma as a possible cause for myasthenia. Usually it is ordered in old age, when the thymoma is usually the causative factor.
Right Answer A
Explanation Educational Objective:

Tensilon test is the first bed site test to evaluate a myasthenia gravis.

References: First Aid for STEP 2 2013, Rheumatology Chapter.
Educational Objective:

Approved No
Keyword Tensilon test
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