USMLE-Rx Step 1 Practice Q's

USMLE-Rx Step 1 Qmax Challenge #1640

Check out today’s Step 1 Qmax Question Challenge.

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USMLE-Rx Step 1 Qmax Challenge #1640A 69-year-old smoker presents with double vision, lower extremity muscle weakness that improves with exertion, and diminished deep tendon reflexes. Results of neurologic, cardiovascular, and ophthalmologic examinations are negative. An X-ray of the chest is shown. A full cancer work-up reveals metastases throughout the body.

Which of the following is the most likely cause for this man’s diplopia and weakness?

A. Antibodies against presynaptic calcium channels at the neuromuscular junction
B. Autoantibodies to acetylcholine receptors at the neuromuscular junction
C. Autoimmune disease with anti-double-stranded DNA, anti-DNA, and anti-Smith antibodies
D. Inflammatory disorder of synovial joints with pannus formation
E. Reactivation of a peripheral subpleural parenchymal lesion and hilar lymph nodes

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4 replies »

  1. I do not see any answer choices to choose from. My guess is that lower extremity muscle weakness (that improves with exertion), diplopia, lung cancer (shown on X-ray), older pt who smokes is related to Lambert-Eaton syndrome.

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  2. Shree,

    Myasthenia weakness tends to worsen with muscle use. Lambert-Eaton myasthenic syndrome is usually associated with “proximal muscle weakness . . . improves with muscle use/[exertion]” (First Aid 2015, pg 435).

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  3. A. Antibodies against presynaptic calcium channels at the neuromuscular junction
    B. Autoantibodies to acetylcholine receptors at the neuromuscular junction
    C. Autoimmune disease with anti-double-stranded DNA, anti-DNA, and anti-Smith antibodies
    D. Inflammatory disorder of synovial joints with pannus formation
    E. Reactivation of a peripheral subpleural parenchymal lesion and hilar lymph nodes

    The correct answer is A. This patient is 69 years old and presents with diplopia, weakness in his lower extremities that improves with exertion, and diminished deep tendon reflexes. He has a history of smoking, and a cancer work-up reveals metastasis throughout the patient’s body.

    His X-ray shows a central lung cancer, which is likely the primary malignancy. His proximal muscle weakness, decreased deep tendon reflexes, and diplopia point toward a paraneoplastic syndrome.

    B is not correct. Myasthenia gravis involves the production of autoantibodies to acetylcholine receptors at the neuromuscular junction and is occasionally seen with thymoma. Symptoms often include muscle weakness and diplopia. Muscle weakness worsens with use in MG, whereas this patient finds that muscle weakness improves with exertion.

    C is not correct. Systemic lupus erythematosus is associated with multiple symptoms, including skin rash, hair loss, fever, and anorexia, which are not reported in this patient. The patient is a 66-year-old man, and this condition is usually seen in females 14–45 years old.

    D is not correct. This describes rheumatoid arthritis (RA). RA manifests with symmetric morning stiffness, joint inflammation, and systemic symptoms (fever and fatigue), which are not seen in this patient. The disease is also seen mostly in females.

    E is not correct. This describes secondary tuberculosis, which is uncommon except in immunocompromised patients. This patient has evidence of a primary tumor with metastases, making tuberculosis highly unlikely.

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