Myasthenia Gravis

A 50-year-old man comes to the physician because of diffuse weakness for the past several months. A lateral chest x-ray that was recently obtained as part of a pre-employment medical evaluation shows an anterior mediastinal mass. He has gastroesophageal reflux disease. His only medication is rabeprazole. He is 178 cm (5 ft 10 in) tall and weighs 77 kg (170 lb); BMI is 24 kg/m². Vital signs are within normal limits. There is no cervical or axillary lymphadenopathy. Cardiopulmonary examination shows no abnormalities. The abdomen is soft and nontender; there is no splenomegaly. Further evaluation of this patient is most likely to show which of the following?

A 63-year-old man comes to the physician for the evaluation of difficulty walking for the last 6 months. He reports weakness in his lower legs that improves with exercise and throughout the day. Three months ago, he started adding flax seeds to his breakfast because he is frequently constipated. He has hypertension and type 2 diabetes mellitus. He has smoked 2 packs of cigarettes daily for the last 45 years. His current medications include enalapril and metformin. Vital signs are within normal limits. Examination shows dry mucous membranes. Muscle strength in the lower extremities is decreased. Sensation to pinprick and light touch is normal. Deep tendon reflexes are 1+ bilaterally. Active muscle contraction or repeated muscle tapping increases reflex activity. Which of the following is most likely to confirm the diagnosis?

A 34-year-old woman is brought to the emergency department because of a 3-hour history of weakness, agitation, and slurred speech. She speaks slowly with frequent breaks and has difficulty keeping her eyes open. Over the past three days, she has had a sore throat, runny nose, and low-grade fever. She says her eyes and tongue have been “heavy” for the past year. She goes to bed early because she feels too tired to talk or watch TV after dinner. She appears pale and anxious. Her temperature is 38.0°C (100.4°F), pulse is 108/min, respirations are 26/min and shallow, and blood pressure is 118/65 mm Hg. On physical examination, there is bluish discoloration of her lips and around the mouth. Her nostrils dilate with every breath. The lungs are clear to auscultation. There is generalized weakness of the proximal muscles. Which of the following is the most appropriate next step in management?

A 51-year-old woman with hyperlipidemia comes to the physician because of weakness for one month. At the end of the day, she feels too fatigued to cook dinner or carry a laundry basket up the stairs. She also complains of double vision after she reads for long periods of time. All of her symptoms improve with rest. Her only medication is pravastatin. Physical examination shows drooping of the upper eyelids. Strength is initially 5/5 in the upper and lower extremities but decreases to 4/5 after a few minutes of sustained resistance. Sensation to light touch is intact and deep tendon reflexes are normal. Which of the following best describes the pathogenesis of this patient's condition?

A 63-year-old man comes to the physician for blurry vision and increased difficulty walking over the past month. He feels very fatigued after watering his garden but feels better after taking a nap. He has not had any recent illness. He has smoked one pack of cigarettes daily for 35 years. Examination shows drooping of the upper eyelids bilaterally and diminished motor strength in the upper extremities. Sensation to light touch and deep tendon reflexes are intact. An x-ray of the chest shows low lung volumes bilaterally. A drug with which of the following mechanisms of action is most appropriate for this patient?

A 53-year-old man comes to the physician because of a 3-month history of cough and progressively worsening difficulty walking up the stairs in his apartment. He has noticed that it is easier for him to climb the stairs after he has exercised. He has also had a 4.6-kg (10-lb) weight loss over the past 6 months. He has smoked one pack of cigarettes daily for 35 years. Examination shows dry mucous membranes. The pupils are equal and react sluggishly to light. Muscle strength in the proximal lower extremity is initially 3/5 but increases to 5/5 after repeated muscle tapping. His Achilles reflex is 1+. Which of the following is the most likely diagnosis?

A 59-year-old woman comes to the physician because of upper extremity weakness and fatigue for the past 4 months. She has had difficulty combing her hair and lifting objects. She has also had difficulty rising from her bed in the mornings for 2 months. Over the past month, she started using over-the-counter mouth rinses for dry mouth. She has smoked 1 pack of cigarettes daily for 40 years. Examination shows decreased deep tendon reflexes. Repetitive muscle tapping shows increased reflex activity. There are no fasciculations or muscle atrophy. A low-dose CT scan of the chest shows a 3-cm mass with heterogeneous calcifications in the center of the right lung. Which of the following is the most likely underlying mechanism responsible for this patient’s current symptoms?

A 28-year-old woman comes to the physician because of a 1-year history of progressive weakness. During this time, she has had increasing difficulty climbing the stairs to her 5th-floor apartment, worsening double vision, and fatigue. There is no personal or family history of serious illness. She works as a teacher and finds it increasingly difficult to pursue her occupation because of her symptoms. She has smoked two packs of cigarettes daily for 10 years. Temperature is 36.5°C (97.7°F), pulse is 62/min, and blood pressure is 120/60 mm Hg. Examination of the heart and lungs shows no abnormalities. Muscle strength is 3/5 on abduction of the shoulders and flexion of the hips, and 4/5 in the remaining muscle groups of all extremities. Sensation is intact bilaterally. Deep tendon reflexes are 2+ and symmetric. On cranial nerve examination, there is drooping of the upper eyelids and she reports double vision when moving her eyes. Placement of an ice pack on her eyelids for 2 minutes improves the eyelid drooping. Her serum thyroid-stimulating hormone (TSH) concentration is 4.2 μU/mL. Results of other screening laboratory studies are within the reference ranges. Which of the following is the most likely diagnosis?