MSK Flashcards
A 55-year-old woman is having a thymectomy done for the treatment of her symptoms. She has a history of double vision that worsens near the end of the day. On physical examination, the patient has drooping eyelids, as well as difficulty talking and swallowing. She has a nasal tone in her voice, and weakness in the upper extremities is noticed. Administering a small amount of edrophonium results in the improvement of symptoms. What is the most likely diagnosis?
A. Guillain-Barre syndrome (GBS)
B. Botulism
C. Lambert-Eaton myasthenic syndrome (LEMS)
D. Myasthenia gravis
The most likely diagnosis, in this case, is myasthenia gravis. Myasthenia gravis is an autoimmune disorder, characterized by descending paralysis with normal deep tendon reflexes. It is a chronic neuromuscular disease that leads to skeletal muscle weakness and fatigue. Skeletal muscles innervated by cranial nerves are most commonly affected, thus causing extraocular and facial muscle weakness. Bulbar and oropharyngeal weakness may result in difficulties in talking, chewing, and swallowing, and an increased risk of pulmonary aspiration of gastric or oral contents. The symptoms worsen with physical activity or throughout the day and improve after rest. Autoimmune destruction of nicotinic acetylcholine receptors at the neuromuscular junction is the most likely mechanism involved in the pathogenesis of this disorder. Myasthenia gravis is often associated with an enlarged thymus gland. Thymectomy may improve symptoms in certain cases.
Guillain-Barre syndrome (GBS) is an acute, autoimmune, and often severe polyradiculopathy that is characterized by ascending paralysis with a loss of deep tendon reflexes.
Botulism, caused by clostridium botulinum, is also characterized by descending muscle paralysis similar to myasthenia gravis. However, edrophonium (tensilon) test can help distinguish the two conditions.
Lambert-Eaton myasthenic syndrome (LEMS) is associated with muscle weakness that improves with physical activity and worsens after rest.
A 21-year-old woman is scheduled to undergo tonsillectomy. She has recently been diagnosed with myasthenia gravis and is using pyridostigmine for her symptoms. She seems to be responding well to the treatment. No other comorbidities are present. Which of the following statements best describes the use of anticholinesterase medications for myasthenia gravis in the perioperative period?
A. Anticholinesterase medications should be discontinued 6 hours prior to surgery
B. Their dose should be reduced in the perioperative period
C. An increased dose of anticholinesterase medications is required for surgery
D. The usual dose of anticholinesterases should be continued in the perioperative period
Anticholinesterase medications should be continued according to the usual dosage during the immediate perioperative period in patients with myasthenia gravis. Myasthenia gravis is an autoimmune neuromuscular disorder characterized by muscle weakness and fatigue.
Anticholinesterase medications, such as pyridostigmine, and neostigmine, are used for the symptomatic treatment of myasthenia gravis. Patients with myasthenia gravis who are maintained on anticholinesterase medications can be quite sensitive to the discontinuation of the medication and may be at an increased risk of developing respiratory and bulbar weakness if the medication is withheld. Therefore, even though anticholinesterases may cause bradycardia, salivation, and altered effects of neuromuscular blocking agents, the patients should keep taking them in the perioperative period according to the usual regimen.
However, the drug interactions of anticholinesterase medications with neuromuscular blocking agents should be kept in mind, and the patients should be informed about the possibility of postoperative ventilator support. Avoidance of drugs that can exacerbate the symptoms of myasthenia gravis is also necessary.
A 57-year-old woman is scheduled to undergo mastectomy for breast carcinoma. The patient has a history of myasthenia gravis. She is taking pyridostigmine, and her symptoms are under control. She also has type II diabetes and is taking insulin. Her lab tests, ECG, chest X-ray, and pulmonary function tests are normal. Which of the following statements best describes the use of succinylcholine in patients with myasthenia gravis?
A. Succinylcholine is absolutely contraindicated in patients with myasthenia gravis
B. Effects of succinylcholine may be prolonged by anticholinesterase medications
C. Smaller doses of succinylcholine are required in myasthenia patients
D. Myasthenia patients have increased sensitivity towards succinylcholine
The effects of succinylcholine may be prolonged by anticholinesterase medications. Myasthenia gravis is an autoimmune neuromuscular disorder characterized by muscle weakness and fatigue. Anticholinesterase medications, such as pyridostigmine, and neostigmine, are used for the symptomatic treatment of myasthenia gravis.
Succinylcholine is a muscle relaxant used to cause short-term paralysis as a part of general anesthesia. It is a depolarizing neuromuscular blocking agent that works by blocking the action of acetylcholine on skeletal muscles. It is metabolized by plasma cholinesterase. Therefore, a decrease in cholinesterase activity achieved by anticholinesterase medications may prolong the effects of succinylcholine.
Succinylcholine is not absolutely contraindicated in myasthenia patients and can be used for rapid tracheal intubation if its administration is absolutely necessary. However, larger doses are required in patients with myasthenia gravis, because of the decreased number of functional acetylcholine receptors.
Myasthenic patients have increased sensitivity towards non-depolarizing neuromuscular blockers, which should, therefore, be used with great caution in patients with myasthenia gravis.
A 35-year-old man is scheduled to have anesthesia evaluation for inguinal hernia repair. A day before the evaluation, he presents with complaints of “heaviness” of the legs that started two days ago. The patient gives a history of loose stools about three weeks ago. Diarrhea resolved on its own. On neurologic examination, bilateral lower extremity weakness and a loss of deep tendon reflexes are noticed. Which of the following is the most likely diagnosis?
A. Myasthenia gravis
B. Guillain Barre syndrome (GBS)
C. Botulism
D. Amyotrophic lateral sclerosis (ALS)
Guillain-Barre syndrome (GBS) is the most likely diagnosis in this patient. GBS is an acute, autoimmune, and often severe polyradiculopathy that involves damage to the peripheral nervous system. The hallmark signs of GBS include an acute ascending flaccid paralysis, i.e., muscle weakness beginning in the lower extremities and moving upwards, accompanied by a loss of deep tendon reflexes. In addition to motor weakness, sensory disturbances, such as pain or tingling dysesthesias may also be present. A history of a respiratory or gastrointestinal infection, about one to three weeks before the onset of symptoms, is usually reported. The underlying mechanism involves the autoimmune destruction of the myelin insulation of peripheral nerves.
Myasthenia gravis is an autoimmune, descending paralysis with normal deep tendon reflexes.
Botulism, caused by clostridium botulinum, is also characterized by descending muscle paralysis.
Amyotrophic lateral sclerosis (ALS) is a motor neuron disease that involves muscle weakness, atrophy, and muscle spasms caused by the degeneration of upper and lower motor neurons.
A 60-year-old man is scheduled to undergo surgery for colorectal carcinoma. He is a known hypertensive and is taking lisinopril for it. His blood pressure is well maintained. He has also been diagnosed with Lambert-Eaton myasthenic syndrome (LEMS) and is taking a combination of pyridostigmine and diaminopyridine. Which of the following malignancies is most likely to be found in association with LEMS?
A. Lymphosarcoma
B. Small-cell lung carcinoma
C. Malignant thymoma
D. Prostate carcinoma
Lambert-Eaton myasthenic syndrome (LEMS) is most commonly associated with small-cell carcinoma of the lung. LEMS is a rare autoimmune, neuromuscular disorder that is characterized by muscle weakness and fatigability, generally of the proximal lower extremities, which improves after brief physical effort and worsens after rest. Autoantibody formation against presynaptic voltage-gated calcium channels at the neuromuscular junction leads to a decreased release of acetylcholine and is the underlying pathologic mechanism in LEMS. LEMS is frequently associated with lung cancer, specifically small-cell carcinoma, making LEMS a paraneoplastic syndrome. LEMS associated with lung carcinoma may be more severe.
Other less frequently associated malignancies include non-small cell lung carcinoma, lymphosarcoma, malignant thymoma, or carcinoma of the breast, stomach, colon, prostate, etc. In most of the LEMS patients with associated cancer, symptomatic onset of myasthenia precedes the diagnosis of cancer. However, LEMS can also occur without associated cancer. Autoimmune diseases, such as hypothyroidism or type I diabetes mellitus, may also be found in association with LEMS.
