386 Emergency Medicine
the vertebrobasilar system can present with vertigo but is an unlikelydiagnosis
in this case of recurrent positional vertiginous symptoms.
347.The answer is a.(Rosen, p 1522.)High clinical suspicion in this case
is for myasthenia gravis,an autoimmune condition in which acetylcholine
receptor antibodiesblock acetylcholine binding and prevent normal neu-
romuscular conduction. The disease typically affects young women and older
men and presents with generalized weakness worsening with repetitive
muscle use that is usually relieved with rest.Ptosis and diplopia are usually
present. The edrophonium testis used to help diagnose myasthenia gravis. It
involves administering edrophonium, a short-acting anticholinesterase, which
prevents acetylcholine breakdown. With the increased acetylcholine levels
at the neuromuscular junction, the patient experiences a subjective and
objective improvement of symptoms by preventing rapid breakdown of
acetylcholine at the myoneural junction. Serologic testing (b)for antibodies
to acetylcholine receptors is useful when positive and should be obtained
in the workup of this patient. A negative test does not exclude the disorder.
The electromyogram is diagnostic.(c)You may consider a CT scan to evalu-
ate the patient for possible mass lesion or aneurysm that is causing her ptosis
and diplopia. However, the clinical scenario is more consistent with myas-
thenia gravis.(d)An electrolyte panel will likely be normal.(e)If the edro-
phonium test is normal, a lumbar puncture should be considered.
348.The answer is b.(Rosen, pp 120-122.)The patient has a progressive
ascending peripheral neuropathy,also known as Guillain-Barrésyndrome.
Peripheral vertigo Central vertigoPathophysiology Disorder of vestibular Disorder of brain
nerve (CN VIII) stem or cerebellum
Severity Intense Less intense
Onset Sudden Slow
Pattern Intermittent Constant
Nausea and vomiting Usually present Usually absent
Exacerbated by position Most of the time Less of the time
Hearing abnormalities May be present Usually absent
Focal neurologic deficits Usually absent Usually present
Fatigability of symptoms Yes No
Nystagmus Horizontal, vertical, Vertical
rotary