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{{WBRQuestion
{{WBRQuestion
|QuestionAuthor={{Rim}}
|QuestionAuthor= {{YD}} (Reviewed by  {{YD}})
|ExamType=USMLE Step 1
|ExamType=USMLE Step 1
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
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|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|SubCategory=Musculoskeletal/Rheumatology
|SubCategory=Musculoskeletal/Rheumatology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
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|MainCategory=Pathophysiology
|MainCategory=Pathophysiology
|SubCategory=Musculoskeletal/Rheumatology
|SubCategory=Musculoskeletal/Rheumatology
|Prompt=A 26 year old female patient, previously healthy, presents to the physician's office complaining of generalized weakness. The patient explains that she also has drooping of the eyelids with difficulty chewing and swallowing her foods. Additionally, she complains of having a "flat" smile that started with her other symptoms. When asked, the patient denies any shortness of breath. Physical examination shows progressive weakness of her extremities upon repetitive movement. Which of the following factors does not necessarily correlate with a more severe disease in this patient's condition?
|Prompt=A 26-year-old woman with no past medical history presents to the physician's office with complaints of generalized weakness for the past 4 weeks. The patient explains that she has recently noticed her eyelids have drooped down, and she has been having difficulty chewing and swallowing her foods. She also complains she has been having a "flat" smile that she never noticed in the past. When asked, the patient denies any shortness of breath or chest pain. Physical examination is remarkable for progressive bilateral weakness of the upper extremities upon repetitive movement. Which of the following factors is not associated with the severity of symptoms in this patient's condition?
|Explanation=The patient presents with signs and symptoms consistent with myasthenia gravis (MG). MG is characterized by a decrease in the numbers of the acetylcholine receptors at the neuromuscular junction. The quantity of receptor loss correlates with the severity of the disease and intensity of symptoms, manifested by muscle weakness.
|Explanation=Myasthenia gravis (MG) is an autoimmune disorder characterized by a decrease in the numbers of the acetylcholine receptors at the neuromuscular junction. Physiologically, acetylcholine binds to its cationic receptor, which in turn, is stimulated to open temporarily, and an electrical potential is generated when the receptors open. The electrical potentials in the end-plate normally generate enough power to cause an action potential given the abundance of available receptors. In patients with MG, the decreased available receptors fail to produce sufficient electrical power to generate an action potential. MG manifests with symptoms of neuromuscular fatigue, whereby repeated contractions result in a progressive decrease of transmission of electric signals following repetitive stimulation ("acetylcholine rundown" phenomenon). The quantity of receptor loss is associated with a more severe disease and worse outcomes among patients with MG. The immunopathogenesis of MG is based on the presence of antibodies that target acetylcholine receptors at the post-synaptic neuromuscular junction. However, the amount of acetylcholine receptor antibodies is not associated with the severity of the disease or worse outcomes.
 
|AnswerA=Involvement of more organs beyond the eyes
Physiologically, acetylcholine binds to its cationic receptor, causing the latter to open temporarily. An electrical potential is generated when the receptors open. The electrical potentials in the end-plate normally generate enough power to cause an action potential due to the abundance of available receptors. In the case of MG, the decreased available receptors will fail to produce sufficient electrical power to generate an action potential. The immunopathogenesis of MG is based on the presence of antibodies that target acetylcholine receptors at the post-synaptic neuromuscular junction. However, the amount of acetylcholine receptor antibodies does not correlate with the severity of the disease.
|AnswerAExp=Myasthenia gravis (MG) grading of severity is based on clinical features. While MG limited to ocular manifestations is grade I, whereas MG with myasthenic crisis or involvement of the diaphragm is grade IV.
 
|AnswerB=Greater quantity of antibodies against target receptors
MG is also characterized by "neuromuscular fatigue", a condition whereby repeated contractions lead to progressive decrease of transmission of electric signals due to decreased amount of released acetylcholine following repetitive stimulation. This phenomenon is called "acetylcholine rundown", which is physiologically seen in normal individuals, but is usually clinically manifested in patients with MG to the baseline decreased numbers of receptors.
|AnswerBExp=The concentration of IgG antibodies that target acetylcholine receptors is not associated with the severity of the disease. In contrast, the function of the antibodies is more important than their quantity. Antibody function, namely the acceleration of receptor degradation, is associated with disease severity.
|AnswerA=Involvement of more organs beyond ocular symptoms
|AnswerC=Fewer available receptors at the level of the muscle
|AnswerAExp=Grading of myasthenia gravis (MG) is based on clinical features. Mere ocular findings are considered grade I MG, whereas involvement of the diaphragm is considered myasthenia crisis or grade IV.
|AnswerCExp=The availability of acetylcholine is inversely associated with the severity of symptoms.
|AnswerB=Quantity of antibodies against target receptors
|AnswerBExp=The level of IgG antibodies that target acetylcholine receptors does not necessarily correlate with the severity of the disease. In contrast, the function of the antibodies is more important than their quantity. Their function and the acceleration of degradation of receptors is thus associated with severity of disease.
|AnswerC=Quantity of available receptors at the level of the muscle.
|AnswerCExp=Availability of acetylcholine receptors correlates directly with the severity of symptoms. As the number of receptors is reduced, MG becomes more severe.
|AnswerD=Difficulty of breathing
|AnswerD=Difficulty of breathing
|AnswerDExp=Involvement of the diaphragm is the hallmark of severe myasthenia crisis.
|AnswerDExp=Involvement of the diaphragm is the hallmark of severe myasthenia crisis.
|AnswerE=Female gender
|AnswerE=Need for plasma exchange
|AnswerEExp=Females are more commonly affected by MG. However, female gender is not associated with more severe disease.
|AnswerEExp=Plasma exchange in MG is usually reserved for severe cases only.
|EducationalObjectives=Myasthenia gravis (MG) is an autoimmune disorder characterized by a decrease in the numbers of the acetylcholine receptors at the neuromuscular junction. The concentration of IgG antibodies that target acetylcholine receptors is not associated with the severity of the disease.
|References=Drachman DB. Myasthenia gravis. N Engl J Med. 1994; 330:1797-1810.<br>
First Aid 2014 page 429
|RightAnswer=B
|RightAnswer=B
|WBRKeyword=myasthenia, gravis, receptor, receptors, antibody, antibodies, IgG, acetylcholine, autoimmune, repetitive, muscle, weakness, fatigue, fatiguability, ocular, extraocular
|WBRKeyword=Myasthenia gravis, Receptors, IgG antibodies, Autoimmune disorder, Acetylcholine receptor, Acetylcholine rundown
|Approved=No
|Approved=Yes
}}
}}

Latest revision as of 01:36, 28 October 2020
Author [[PageAuthor::Yazan Daaboul, M.D. (Reviewed by Yazan Daaboul, M.D.)]]
Exam Type ExamType::USMLE Step 1
Main Category MainCategory::Pathophysiology
Sub Category SubCategory::Musculoskeletal/Rheumatology
Prompt [[Prompt::A 26-year-old woman with no past medical history presents to the physician's office with complaints of generalized weakness for the past 4 weeks. The patient explains that she has recently noticed her eyelids have drooped down, and she has been having difficulty chewing and swallowing her foods. She also complains she has been having a "flat" smile that she never noticed in the past. When asked, the patient denies any shortness of breath or chest pain. Physical examination is remarkable for progressive bilateral weakness of the upper extremities upon repetitive movement. Which of the following factors is not associated with the severity of symptoms in this patient's condition?]]
Answer A AnswerA::Involvement of more organs beyond the eyes
Answer A Explanation AnswerAExp::Myasthenia gravis (MG) grading of severity is based on clinical features. While MG limited to ocular manifestations is grade I, whereas MG with myasthenic crisis or involvement of the diaphragm is grade IV.
Answer B AnswerB::Greater quantity of antibodies against target receptors
Answer B Explanation [[AnswerBExp::The concentration of IgG antibodies that target acetylcholine receptors is not associated with the severity of the disease. In contrast, the function of the antibodies is more important than their quantity. Antibody function, namely the acceleration of receptor degradation, is associated with disease severity.]]
Answer C AnswerC::Fewer available receptors at the level of the muscle
Answer C Explanation AnswerCExp::The availability of acetylcholine is inversely associated with the severity of symptoms.
Answer D AnswerD::Difficulty of breathing
Answer D Explanation AnswerDExp::Involvement of the diaphragm is the hallmark of severe myasthenia crisis.
Answer E AnswerE::Need for plasma exchange
Answer E Explanation AnswerEExp::Plasma exchange in MG is usually reserved for severe cases only.
Right Answer RightAnswer::B
Explanation [[Explanation::Myasthenia gravis (MG) is an autoimmune disorder characterized by a decrease in the numbers of the acetylcholine receptors at the neuromuscular junction. Physiologically, acetylcholine binds to its cationic receptor, which in turn, is stimulated to open temporarily, and an electrical potential is generated when the receptors open. The electrical potentials in the end-plate normally generate enough power to cause an action potential given the abundance of available receptors. In patients with MG, the decreased available receptors fail to produce sufficient electrical power to generate an action potential. MG manifests with symptoms of neuromuscular fatigue, whereby repeated contractions result in a progressive decrease of transmission of electric signals following repetitive stimulation ("acetylcholine rundown" phenomenon). The quantity of receptor loss is associated with a more severe disease and worse outcomes among patients with MG. The immunopathogenesis of MG is based on the presence of antibodies that target acetylcholine receptors at the post-synaptic neuromuscular junction. However, the amount of acetylcholine receptor antibodies is not associated with the severity of the disease or worse outcomes.

Educational Objective: Myasthenia gravis (MG) is an autoimmune disorder characterized by a decrease in the numbers of the acetylcholine receptors at the neuromuscular junction. The concentration of IgG antibodies that target acetylcholine receptors is not associated with the severity of the disease.
References: Drachman DB. Myasthenia gravis. N Engl J Med. 1994; 330:1797-1810.
First Aid 2014 page 429]]

Approved Approved::Yes
Keyword WBRKeyword::Myasthenia gravis, WBRKeyword::Receptors, WBRKeyword::IgG antibodies, WBRKeyword::Autoimmune disorder, WBRKeyword::Acetylcholine receptor, WBRKeyword::Acetylcholine rundown
Linked Question Linked::
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