A 31-year-old woman comes to the office due to vision disturbances. The patient is a software developer and works on a computer most of the time. She first noticed blurry vision 2 months ago. Since then, she has had several episodes of blurry and double vision, especially toward the end of the workday. Two days ago, she experienced neck discomfort and had difficulty holding her head up, which resolved after a night's rest. The patient does not use tobacco, alcohol, or illicit drugs. Vital signs are within normal limits. On physical examination, pupils are 3 mm, round, and reactive to light. There is no ptosis, and ocular movements are normal. No neck deformity or tenderness is present. Muscle strength, deep tendon reflexes, and sensation are normal in the bilateral upper and lower extremities. Further evaluation reveals antibodies directed against nicotinic receptors on the motor endplate. Which of the following is the most appropriate next step in evaluation of this patient?

Question

A 31-year-old woman comes to the office due to vision disturbances.  The patient is a software developer and works on a computer most of the time.  She first noticed blurry vision 2 months ago.  Since then, she has had several episodes of blurry and double vision, especially toward the end of the workday.  Two days ago, she experienced neck discomfort and had difficulty holding her head up, which resolved after a night's rest.  The patient does not use tobacco, alcohol, or illicit drugs.  Vital signs are within normal limits.  On physical examination, pupils are 3 mm, round, and reactive to light.  There is no ptosis, and ocular movements are normal.  No neck deformity or tenderness is present.  Muscle strength, deep tendon reflexes, and sensation are normal in the bilateral upper and lower extremities.  Further evaluation reveals antibodies directed against nicotinic receptors on the motor endplate.  Which of the following is the most appropriate next step in evaluation of this patient?

Quizplus · Accepted Answer

11ec25c8_d5b6_8cbd_bc81_a7582ae0b54a_MD0003_00 This patient with fatigable diplopia and neck weakness that resolved with rest has myasthenia gravis (MG), a neuromuscular disorder caused by autoantibodies directed against nicotinic acetylcholine receptors at the neuromuscular junction. Patients classically experience fluctuating and fatigable weakness that involves the ocular (eg, diplopia, ptosis) and/or bulbar (eg, dysphagia, dysarthria) muscles, is often worse at the end of the day, and resolves with rest. Confirmatory diagnosis is with testing for acetylcholine receptor (AChR) antibodies, which are highly specific. Patients with established MG should undergo chest imaging (eg, CT scan, MRI) to evaluate for a thymoma. The thymus is involved in differentiation of T cells, which can stimulate B cells/antibody production and which can bind to AChR. Thymic abnormalities are seen in most patients with AChR antibodies, with thymic hyperplasia in ~70% and thymoma in ~15% of cases. Chest imaging helps with possible surgical planning, as thymectomy is associated with long-term clinical improvement in both patients with and without thymoma (Choice F). thymoma (Choices A and E) Cerebrospinal fluid analysis and MRI of the brain can be used to evaluate for demyelinating diseases (eg, multiple sclerosis). MRI may be considered to evaluate for central nervous system lesions (eg, tumor, stroke) in patients with diplopia. However, acetylcholine receptor antibodies are not characteristic of these diseases. (Choice B) Cervical spine imaging can detect cervical spondylosis, which can cause neck pain and cervical radiculopathy, resulting in weakness of associated myotomes (typically in the arm or shoulder). However, the weakness would not fluctuate, and vision would not be affected. (Choice D) Echocardiography is used to evaluate cardiac and valvular structure and function (ie, ejection fraction). It is not used to assess the thymus and is less specific than chest imaging, (Choice G) Slit-lamp ocular examination is typically used to evaluate for abnormalities of the anterior segment of the eye (eg, conjunctiva, cornea, anterior chamber, iris). This patient's normal eye examination and absence of pain or redness make anterior eye abnormalities unlikely. Educational objective: Individuals with features of myasthenia gravis (eg, fluctuating and fatigable ocular/bulbar weakness) should undergo confirmatory testing with acetylcholine receptor antibodies, which are highly specific. Those with an established diagnosis should subsequently undergo chest imaging (eg, CT scan, MRI) to evaluate for thymoma and for possible surgical planning, as thymectomy is associated with long-term clinical improvement in both patients with and without thymoma. References: Myasthenia gravis: a review. (http://www.ncbi.nlm.nih.gov/pubmed/23193443)

A 31-Year-Old Woman Comes to the Office Due to Vision