United States Medical Licensing Step 3: USMLE-STEP-3

Correct Answer: E Section: (none)

Explanation:

COPD is a group of chronic and progressive pulmonary disorders that cause reduced expiratory flow. Most of the obstruction is fixed, although some reversibility can be found. COPD affects approximately 16 million Americans and smoking is, by far, the greatest risk factor. Onset is typically in the fifth decade and the typical presenting symptoms are dyspnea and cough. Patients often relate these to an acute illness (walking pneumonia in this case) but the decline in pulmonary function has been present for some time prior to the onset of symptoms. The physical examination has poor sensitivity and may, in early disease, only show wheezing on forced expiration and a prolonged expiratory phase of respiration. Clubbing is not typically a manifestation of COPD and its presence should lead to a search for another cause, such as lung cancer. In the setting of pulmonary hypertension, sometimes one can hear a pronounced pulmonic component to the second heart sound, although hyperinflation may obscure this finding. Bilateral pulmonary crackles would be more consistent with pulmonary edema. Supraclavicular adenopathy should lead to a workup to exclude cancer, especially of breast, lung, ovarian, or GI origin. Hyperinflation of the lungs is the most likely CXR finding in this case. This would manifest as flattened diaphragms with elongated lungs and a long, narrow cardiac shadow. Kerley B lines would be more characteristic of pulmonary edema from left-sided heart failure, rather than COPD. A pulmonary mass with adenopathy would be more consistent with lung cancer--certainly a possibility in a long-time smoker, but much less common than COPD. A residual infiltrate from pneumonia a year ago would be highly unlikely.

Correct Answer: D Section: (none)

Explanation:

Menstrual disorders, primarily oligo-and amenorrhea, are particularly common among women with eating disorders and are thought to be the result of hypothalamic hypoestrogenism. This patient demonstrates estrogen deficiency (decreased breast size, urogenital atrophy). Her dental caries, oral sores, and hand sores might be a result of self-induced vomiting. Hyperthyroidism would be considered in the differential diagnosis of a young woman with weight loss and menstrual irregularities. In contrast to persons with a medical condition that causes weight loss, those with an eating disorder express a disordered body image and, often, a desire to be underweight. This patient requires additional investigation to assess for the possibility of inpatient admission. Patients with a prolonged, severe eating disorder are at risk for developing dehydration, electrolyte imbalance (especially hypokalemia), cardiac dysrhythmias, and hypothermia. Hospitalization would be considered for those who are severely dehydrated, who have marked electrolyte abnormalities who are <75% of their ideal body weight, or who have a comorbid condition that would require hospitalization, such as a severe psychiatric disorder. Although weight-bearing exercise favors bone formation, when excessive exercise and/or an eating disorder results in amenorrhea, estrogen levels fall. Subsequently, bone mineral density decreases. Persons with eating disorders are at increased risk for comorbid psychiatric conditions including depression, anxiety, obsessive-compulsive disorder, and personality disorders.

Correct Answer: A Section: (none)

Explanation:

Explanations:

Understanding the concepts of sensitivity, specificity, PPV, and NPV is crucial to interpreting diagnostic test

results. Sensitivity is defined as the percentage of people who have a disease who test positive for that

disease. Specificity is defined as the percentage of people who are free of a disease who test negative.

These two concepts are considered characteristics of the specific test in question and are independent of

the prevalence of the disease in the population. The PPVs and NPVs of a test are the test's clinical

characteristics and these concepts are directly related to the prevalence of the disease in the population.

The PPV is the percentage of people who have a positive test result who actually have the disease.

Similarly, the NPV is the percentage of people who have a negative test result who don't have the disease.

While the definitions may seem subtly different, the implications are significant. The usual way to calculate sensitivity, specificity, PPV, and NPV is with the table, using the following definitions

The definitions of sensitivity, specificity, PPV, and NPV would then be:

Sensitivity = a/(a + c)

Specificity = d/(d + b)

PPV = a/(a + b)

NPV = d/(d + c)

The specific information in this question comes from an article describing a study of B-type natriuretic

peptide (BNP) for the diagnosis of CHF. The data presented show that 106 persons tested positive using

the BNP test. After comparison with the "gold standard," in this case, a review by expert cardiologists, 95 of

these 106 were determined to truly have CHF. Therefore, 11 of the 106 were false positives and 95 were

true positives. Similarly, 144 persons tested negative using the BNP test. Of these, 142 were confirmed as

true negatives and 2 were determined to be false negatives.

Putting these numbers into a table reveals:

The calculations then become:

Sensitivity = a/(a + c) = 95/(95 + 2) = 98%

Specificity = d/(d + b) = 142/(142 + 11) = 93%

PPV = a/(a + b) = 95/(95 + 11) = 90%

NPV = d/(d + c) = 142/(142 + 2) = 99%