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Simple Q

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epica

06/16/07 - 10:37 PM

A 45-year-old woman comes to the physician complaining of weakness in her legs for the past 3 months. She has difficulty climbing stairs and rising from a chair. She also states that she has been seeing double on vertical gaze and that her eyes appear droopy. Repetitive nerve stimulation of the femoral nerves at 1 Hertz shows action potential amplitudes in the rectus femoris muscles that are 10 percent of normal. Repetitive stimulation at 30 Hertz shows a doubling in the action potential amplitudes. Creatine kinase levels are normal. What is the most likely diagnosis?
A. Myasthenia gravis
B. Lambert-Eaton myasthenia syndrome
C. Polymyositis
D. Dermatomyositis
E. Amyotrophic lateral sclerosis

new_n_lost
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06/16/07 - 10:44 PM

B. Lambert-Eaton myasthenia syndrome

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silver
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06/16/07 - 10:44 PM

B. Lambert-Eaton myasthenia syndrome

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epica

06/16/07 - 11:18 PM

Choice (B) is the correct answer. The patient is presenting with Lambert-Eaton myasthenia syndrome which is an autoimmune disease associated with auto-antibodies to voltage-gated calcium channels (VGCC). Weakness is characteristic, particularly in the proximal lower extremities. Approximately 25 percent of patients with LEMS have ocular manifestations, and many patients report dry mouth. Repetitive nerve stimulation shows that with low frequency stimulation, action potential amplitude is significantly abnormal but increases with increased stimulation frequency. Clinically, this is represented by increasing strength with sustained muscle contraction and is a distinguishing feature between LEMS and myasthenia gravis

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