USMLE-STEP-3 Online Practice Questions and Answers

Correct Answer: D Section: (none)

Explanation:

This patient's presentation is consistent with primary syphilis. Primary syphilis manifests itself usually in the form of solitary or multiple raised, firm papules which eventually erode to form ulcerative craters with raised, indurated margins surrounding the centralized ulcer. These lesions, called chancres, most commonly involve the glans penis in males and the vulva or cervix in females, although they may appear rarely in other areas. Syphilis is caused by the spirochete, T. pallidum, which can be visualized by darkfield microscopy, by silver stain, or by fluorescent antibody microscopy. There is an incubation period of approximately 3 weeks separating the time of initial exposure to T. pallidum and the time of chancre formation. Syphilis is characterized by the presence of latent stages in which there are no signs of clinical disease present. Penicillin is the drug of choice for the treatment of syphilis. In addition to treating patients with diagnosed syphilis, it is recommended that treatment also be administered to all sexual contacts of the past 90 days. It has been demonstrated that up to 30% of asymptomatic sexual contacts of patients with infectious lesions within the past 30 days go on to develop syphilis if left untreated. If left untreated, patients may ultimately develop tertiary syphilis characterized by significant destructive neurologic and cardiovascular symptoms. The mortality rate for untreated tertiary syphilis is approximately 20%.

Cephalosporins and penicillin antibiotics act by interfering with the late stages of bacterial cell wall synthesis, although the precise biochemical reactions are not entirely understood. Peptidoglycan provides mechanical stability to the cell wall because of its high degree of cross-linking with alternating amino pyranoside sugar residues (N-acetylglucosamine and N-acetylmuramic acid). The completion of the cross-linking occurs by the action of the enzyme transpeptidase. This transpeptidase reaction, in which the terminal glycine residue of the pentaglycine bridge is joined to the fourth residue of the pentapeptide (Dalanine) thereby releasing the fifth residue (D-alanine), is inhibited by beta-lactams.

Correct Answer: E Section: (none)

Explanation:

This patient has sickle cell anemia. This is evident from sickle cells forms on the peripheral blood smear in Figure 1-13. Pain medication is an important initial concern. It is often difficult to determine whether a patient in sickle cell crisis has an ongoing infection. Infections can precipitate sickle cell crisis. With respect to community-acquired pneumonia, the diagnosis is difficult. A patient with sickle cell crisis can have fever as a result of the sickle crisis. They can have an increased respiratory rate, physical examination, and CXR findings which suggest pneumonia as a result of pulmonary infarctions. A white blood count can be elevated due to marrow stimulation. In the presence of the acute chest syndrome, characterized by chest pain, hypoxia, and CXR infiltrates, antibiotics would be indicated. Without further information, it is hard to decide to empirically start broad-spectrum antibiotics for community-acquired pneumonia. Transfusions should generally be avoided in patients with sickle cell anemia who are not symptomatic due to the anemia. Since patients in sickle cell crisis have intravascular hemolysis, their reticulocyte counts are usually high and they can replace their blood quickly. Repeated small transfusions will lead to autoantibodies that will make further transfusions difficult. Arterial blood gas determination should not be the first step, given the above information. A CT scan of the abdomen is not indicated given the nonspecific nature of the patient's abdominal findings. Parvovirus B19 can cause aplastic crisis in patients with hemoglobinopathies, including sickle cell disease. A tip to this diagnosis is the decreased reticulocyte count in a patient who normally would have a high reticulocyte count. Given the information listed above, there is no indication for broad-spectrum antibiotics. Splenectomy is not a reasonable alternative at this point. Patients with sickle cell disease have autosplenectomy by the time they are adults. A bone marrow biopsy maybe indicated because of the low platelet count, but not initially. GnCSF is not indicated because the patient does not have neutropenia. Patients with sickle cell disease typically have isosthenuria.

This is due to repeated infarction of the renal papilli. This causes destruction and interference with the counter current mechanism that causes urine concentration. As a result, patients with sickle cell anemia have the inability to concentrate their urine. This results in fluid and electrolyte abnormalities. Patients in sickle cell crisis are usually fluid depleted. This and the sickled blood cells cause hyperviscosity and microinfarctions. There is no evidence that the patient has diabetes insipidus, which usually has a urine specific gravity less than 1.005. Patients with UTIs do not have isosthenuria due to RBCs and WBCs that increase the urine specific gravity. Sickle cell patients may have zinc deficiency, but this is not a cause of isosthenuria.

Correct Answer: E Section: (none)

Explanation:

Toxic nodular goiter, also known as Plummer's disease, is a consequence of one or more thyroid nodules secreting inappropriately high levels of thyroid hormone independently of thyroid-stimulating hormone (TSH) control. Hyperthyroidism in patients with toxic nodular goiter is milder than in those with Graves' disease, and the condition is not accompanied by extrathyroidal manifestations such as ophthalmopathy, pretibial myxedema, vitiligo, or thyroid acropathy. Patients with toxic multinodular goiter are older at presentation than those with Graves' disease. The thyroid gland characteristically has one or more nodules on palpation. Local symptoms of compression, such as dysphagia and dyspnea, may occur. The diagnosis is suggested by a thorough history and physical examination and confirmed by documenting suppressed serum TSH level and raised serum thyroid hormone level.

Correct Answer: B Section: (none)

Explanation:

G. lamblia is a common protozoan which can be acquired by ingesting unfiltered water. It is seen frequently in people who drink fresh stream water. It is a cause of chronic, nonbloody diarrhea. There is typically a large amount of gas and cramping associated with Giardia infections. RMSF does not typically cause a gastroenteritis. Children with RMSF will commonly have fevers, headaches, and a petechial rash. Rotavirus and Norwalk viruses typically cause acute, self-limited gastroenteritis. The diarrhea is nonbloody, nonmucousy, and typically lasts a few days. The most appropriate treatment for giardiasis is oral metronidazole. Oral rehydration is an important mainstay in the treatment of diarrhea of any cause but is not a specific treatment for giardiasis. Ciprofloxacin is commonly used for traveler's diarrhea caused by E. coli.

Correct Answer: B Section: (none)

Explanation:

The most common infectious cause of blindness in the world is trachoma. Trachoma is the chronic effect of a C. trachomatis infection acquired in the perinatal period. The most common cause of blindness in the world is noninfectious

Correct Answer: C Section: (none)

Explanation:

Falling on outstretched arms is one of the most common injuries among school-aged children. This can result in a buckle, or torus, fracture of the distal radius and/or ulna. This is a common accidental mechanism and should not, by itself, raise suspicions for an inflicted injury. AP and lateral x-rays of the wrist and elbow would be diagnostic of this type of injury. Nursemaid's elbows occur from a pulling or twisting mechanism to the upper extremity and are not the result of falls. An MRI of this injury would be overkill.

Correct Answer: E Section: (none)

Explanation: VAIN is frequently found in women who have a history of cervical dysplasia. Although the etiology of VAIN has not been thoroughly elucidated, like cervical intraepithelial neoplasia (CIN), it is thought that HPV is the carcinogenic agent. Thus, when vaginal cytology is abnormal, the evaluation is very similar to that of an abnormal pap smear. It is important to assess the histologic severity and the extent of the lesion. To do this, the next step in management is a thorough colposcopic evaluation of the entire vaginal canal, especially because many patients will have multifocal disease.

During colposcopy the application of acetic acid (4%) is useful. The speculum should be fully inserted to visualize the upper vagina and then slowly removed while rotating the speculum, being careful to view the entire vaginal mucosal surface. Most vaginal lesions are not grossly visible. However, a raised white epithelium may occasionally be seen. If a lesion is visible, then directed biopsy of the lesion is indicated to confirm the diagnosis. The image provided shows HGSIL. In the presence of high-grade vaginal cytology, repeat cytology in 6 months, and observation are not viable management options given the concern for carcinoma in situ or for invasive carcinoma of the vagina. Random vaginal biopsies are also not likely to be helpful since they will most likely miss the involved area and lead to a false negative result. Intravaginal estrogen cream is reserved for postmenopausal women with vaginal atrophy and low-grade VAIN without evidence of invasion. Estrogen is not a treatment for VAIN 3, or high-grade VAIN.

Correct Answer: B Section: (none)

Explanation:

Cystic fibrosis is the most common hereditary condition in Whites with a carrier frequency of 1 in 25. The American College of Obstetricians and Gynecologists, the American College of Medical Genetics, and the National Institutes of Health have recommended that cystic fibrosis carrier screening be offered to all White couples either pregnant or considering a pregnancy, and that the availability of screening be discussed with members of other ethnic groups who have a lower frequency of cystic fibrosis carrier state. Cystic fibrosis is inherited in an autosomal recessive fashion, so for a couple in which both mother and father are carriers the risk of having an affected child is 25% or 1 in 4. In the case presented, in which the husband's sister has cystic fibrosis, his likelihood of being a carrier is 2 in 3 (since he has an affected sibling, both of his parents are obligate carriers, and since he is not affected, he is either a noncarrier [1 in 3] or a carrier [2 in 3]). This pattern is true for all autosomal recessive disorders.

Correct Answer: B Section: (none)

Explanation:

This woman likely suffers from major depressive disorder. Treatment with a SSRI is considered to be first-line therapy. Although the neurovegetative symptoms of depression (e.g., insomnia, change in appetite, anergia, poor concentration) can sometimes improve after several days of initiating pharmacotherapy, the feelings of depression and hopelessness may take up to 46 weeks to significantly improve. As long as she is tolerating the SSRI, the urge to quickly increase the dose should be avoided so as to minimize side effects. Upon initiation of a SSRI, education and reassurance should be provided to the patient regarding the expected time until remission. Although there are characteristic side effects, most patients tolerate treatment with SSRIs. Many of these side effects, such as headaches, gastrointestinal disturbances, and vivid dreams, transpire at the start of treatment and may resolve over days to weeks. Sexual dysfunction, such as impotence or inhibited orgasm, not uncommonly occurs after several weeks to months of treatment with SSRIs and can continue with ongoing treatment.

Correct Answer: E Section: (none)

Explanation: Explanations: The Third Report of the National Cholesterol Education Program Expert Panel on the Detection, Evaluation, and Treatment of High Blood Cholesterol in Adults (ATP III) was published in May 2001 by the National Heart, Lung, and Blood Institute of the National Institutes of Health. This evidence-based report provides guidelines for the evaluation and management of blood lipid levels for the primary and secondary prevention of heart disease. The basis of the recommendations for management is an overall evaluation of an individual's risk factors for developing cardiovascular disease. Persons at the highest risk for future cardiac events are those with already established coronary artery disease or "coronary artery disease equivalents," which include diabetes mellitus, other forms of atherosclerotic disease, or multiple risk factors that confer a 10-year CHD risk of greater than 20%. Multiple studies have shown that elevated LDL cholesterol levels are a risk for coronary artery disease and that lowering LDL levels can reduce the risk of events.

ATP III goals are targeted at LDL levels. For persons with LDL levels above this goal, the options for lowering LDL can include therapeutic lifestyle changes, lipid-lowering medications, or a combination of both. In a patient with coronary artery disease, diabetes mellitus, or other CHD equivalents, the LDL goal level is 100 mg/dL. In this population, therapeutic lifestyle changes alone would be recommended for those with LDL levels of 100130 and medication could be started concomitantly with lifestyle changes for those with LDL above 130, as most persons would require medication to achieve the recommended goal. For the patient in this question with an LDL of 160 mg/dL, therapy with an HMG-CoA reductase inhibitor would be recommended first-line therapy to try to get his LDLto goal. Therapeutic lifestyle changes alone would be very unlikely to reduce his LDL to less than 100 mg/dL, but are still an important part of his overall lipid management program and should be recommended along with medication therapy. Neither increasing his dosage of metformin nor adding insulin would be recommended as they would not be expected to improve his dyslipidemia significantly and because his diabetic control is appropriate. At his follow-up visit, the patient's lipid levels have met the recommended guidelines; therefore, the recommendation would be to continue with his current therapy. Increasing the dosage of his statin, adding a fibric acid, nicotinic acid, or referring the patient to a dietician would all be appropriate considerations in someone who had not successfully reached his goal lipid levels.

A recent addition to the ATP III provides an option for changing the target LDL goal for those at the highest of risk for coronary events. For persons with known coronary artery disease, or CAD equivalent, and multiple risk factors, such as diabetes or continued smoking, one could consider using an LDL of 70 as a goal. For this patient, with diabetes but no history of CAD or equivalent, the recommended goal would remain an LDL of 100 or less. Immunizations should be a routine part of the adult health maintenance evaluation. All patients with diabetes are recommended to be vaccinated with the pneumococcal vaccine (PPV-23) both because of the incidence of pneumonia in diabetics and the increased risk of complications should infection occur. A recent recommendation for all adults is to provide a single dose of Tdap vaccine in place of one booster dose of Td. The rationale for this is to attempt to reduce the incidence of pertussis in the population, as pertussis has been recurring in the United States in spite of routine childhood vaccination. Hepatitis A and B are routine vaccinations for children. The current recommendation for adult immunizations against these diseases is to target high-risk adults. Diabetes is not considered a high risk for these infections. Herpes zoster vaccine is recommended for adults over the age of 60