young_doc
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6. A 57-year-old woman is evaluated because of a 6-month history of progressive dyspnea. She has never smoked cigarettes. She has been treated on several occasions for a “COPD exacerbation” with intravenous corticosteroids, with some relief of symptoms. She states that symptoms are particularly bothersome in the evening. Pulmonary function test results are as follows:
Laboratory Studies Forced expiratory volume in 1 sec (FEV1) 2.06 L (84% of predicted)
Forced vital capacity (FVC) 2.74 L (83% of predicted)
FEV1/FVC 75% Maximum voluntary ventilation 63 L/min (65% of predicted)
Maximum inspiratory pressure 39 cm H2O (52% of predicted)
Maximum expiratory pressure 58 cm H2O (42% of predicted)
Total lung capacity 4.01 L (76% of predicted)
Functional residual capacity 2.13 L (72% of predicted)
Residual volume 1.42 L (73% of predicted)
Diffusing lung capacity for carbon monoxide (DLco) 19.39 mL/min/mm Hg (99% of predicted)
Which of the following is the most likely cause of this patient's dyspnea?
( A ) Chronic thromboembolic disease
( B ) Chronic obstructive pulmonary disease
( C ) Idiopathic pulmonary fibrosis
( D ) Myasthenia gravis
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| vradojc1
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Although it's weird for Myastenia to present that late, I'd pick it because of the low pressures - that are mediated by extrinsic factors to the lung (respiratory muscles).
All the other ones should have DLCO affected (although chronic bronchitis-one side of COPD-later in the course)
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| Justice
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( D ) Myasthenia gravis
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| young_doc
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Ans: D
" The patient probably has myasthenia gravis. Spirometry and lung volumes reveal mild restriction. Reduced maximum voluntary ventilation and maximum inspiratory and expiratory mouth pressures suggest muscle weakness. A history of symptoms that worsen during the course of the day also suggests this diagnosis.
Chronic thromboembolic disease and idiopathic pulmonary fibrosis are unlikely in the setting of a normal diffusion capacity. Chronic obstructive pulmonary disease is unlikely in someone who has never smoked, and this diagnosis would not explain the reduced maximum voluntary ventilation and maximum inspiratory and expiratory pressures. "
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