A 38-year-old woman is evaluated in the clinic due to swallowing difficulty that began a month ago while eating dinner. Halfway through the meal, she had difficulty chewing her steak and was unable to swallow it. Since then, the patient has had 2 similar episodes associated with food and water regurgitation through her nose. Medical history is significant for gastroesophageal reflux disease. Blood pressure is 138/76 mm Hg and pulse is 82/min. Oropharyngeal examination is unremarkable. Lung auscultation is normal. Heart sounds are normal with no murmurs. The abdomen is soft and nontender with no organomegaly. The patient has no focal weakness or sensory loss, and reflexes are normal. Upper gastrointestinal endoscopy and esophageal manometry are normal. CT scan of the chest is shown in the image below: Which of the following is the most likely cause of this patient's symptoms?

Question

A 38-year-old woman is evaluated in the clinic due to swallowing difficulty that began a month ago while eating dinner.  Halfway through the meal, she had difficulty chewing her steak and was unable to swallow it.  Since then, the patient has had 2 similar episodes associated with food and water regurgitation through her nose.  Medical history is significant for gastroesophageal reflux disease.  Blood pressure is 138/76 mm Hg and pulse is 82/min.  Oropharyngeal examination is unremarkable.  Lung auscultation is normal.  Heart sounds are normal with no murmurs.  The abdomen is soft and nontender with no organomegaly.  The patient has no focal weakness or sensory loss, and reflexes are normal.  Upper gastrointestinal endoscopy and esophageal manometry are normal.  CT scan of the chest is shown in the image below:  Which of the following is the most likely cause of this patient's symptoms?

Quizplus · Accepted Answer

11ec25c8_d0fa_641b_bc81_f5984403ae4f_MD0003_00 This patient's symptoms are concerning for myasthenia gravis (MG), a neuromuscular disorder that typically presents with fluctuating, fatigable muscle weakness that worsens with repetitive motion and improves with rest. Ocular symptoms (eg, ptosis, diplopia) and bulbar dysfunction are the most common manifestations, the latter of which may lead to fatigable chewing or dysphagia with nasopharyngeal regurgitation, as in this patient. Early in the disorder course, weakness is often limited to specific muscle groups (eg, ocular or bulbar), then becomes generalized (eg, limb and respiratory involvement) over the next 2 years. MG is caused by autoantibodies (originating in the thymus) directed against nicotinic acetylcholine receptors at the neuromuscular junction. Antibody binding leads to complement activation with receptor degradation, causing impaired action potential propagation and muscle weakness. Most patients with acetylcholine receptor antibodies have thymic abnormalities (eg, thymoma, thymic hyperplasia), which may appear as an anterior mediastinal mass on chest imaging. A CT scan of the chest is typically performed in patients with MG to evaluate for thymoma because thymectomy can result in long-term disease remission. (Choice A) Foodborne botulism and Lambert-Eaton syndrome (LES) result in decreased acetylcholine release from the presynaptic terminal of motor neurons, which can affect cranial nerves and cause difficulty swallowing. However, botulism typically causes rapidly progressive, symmetric descending flaccid paralysis, and LES typically causes proximal lower extremity weakness (vs normal strength). Both would be expected to have decreased or absent reflexes (vs normal reflexes). (Choice C) Achalasia occurs due to degeneration of neurons within the myenteric plexus and can cause gradual onset of solid and liquid dysphagia due to uncoordinated peristalsis and failed relaxation of the lower esophageal sphincter (LES). However, esophageal manometry typically reveals high LES resting pressure. (Choice D) Systemic sclerosis is a progressive connective tissue disease characterized by fibrosis of the skin and visceral organs. Esophageal involvement can cause dysphagia due to fibrous tissue replacement of smooth muscle; however, esophageal manometry classically reveals dysmotility and low LES pressure. (Choice E) Multiple sclerosis (MS) is an autoimmune disorder characterized by inflammatory demyelination of axons in the central nervous system, which can lead to variable relapsing-remitting neurologic deficits, including dysphagia. However, initial manifestations are more commonly ocular (eg, optic neuritis, intranuclear ophthalmoplegia) than bulbar, and MS is not associated with a mediastinal mass. Educational objective: Myasthenia gravis is caused by autoantibody-mediated degradation of acetylcholine receptors at the neuromuscular junction, which often leads to fatigable ocular and bulbar muscle weakness. Most patients with acetylcholine receptor antibodies have thymic abnormalities (eg, thymoma), which appear as an anterior mediastinal mass on chest imaging. References: Myasthenia gravis: a review. (http://www.ncbi.nlm.nih.gov/pubmed/23193443)

A 38-Year-Old Woman Is Evaluated in the Clinic Due to Swallowing