USMLE-STEP-3 Online Practice Questions and Answers

Correct Answer: C Section: (none)

Explanation:

This is a clinical presentation of West Nile virus infection. The tongue fasciculations go along with an inflammation at the base of the brain. The patient is at the right age for West Nile virus infection and he is immunocompromised due to diabetes. The diagnosis can be made by performing a West Nile virus IgM titer on the CSF. Diabetics can have cryptococcal meningitis. Lumbar puncture in this setting is usually normal with increased opening pressure, and rhabdomyolysis is not a feature of this disease. Diabetics are more at risk for candidiasis. However, the patient has no history of instrumentation, IV catheters, or other situations that would lead to disseminated candidiasis. Diabetics are at increased risk for C. immitis infection, but we have no history of the patient living in an area endemic for this organism. Diabetics are at increased risk for rhinocerebral mucormycosis. An MRI of the head might have shown involvement of the sinus. However, this patient's presentation is not consistent with rhinocerebral mucormycosis.

Correct Answer: D Section: (none)

Explanation:

The skin lesions as shown in Figures show erythematous maculopapular lesions. There are only a few conditions that cause a rash on the palms and soles. These include syphilis, gonorrhea, and Stevens-Johnson syndrome. Disseminated gonnorhea does not cause lesions on the face. This is not a potential presentation of hepatitis B or chlamydia. Askin biopsy is not indicated. RPR and MHA-TP tests will be positive in syphilis in a high titer. All patients with syphilis need to have HIV testing. The rash of primary HIV infection is a faint erythematous rash on the trunk and is not always present. Early in primary HIV infection, a PCR determination can be negative. In the absence of neurosyphilis, benzthine penicillin 2.4 million units IM weekly for 3 weeks is the treatment of choice for patients with syphilis of unknown duration or greater than a year. While azithromycin 1 g orally will treat gonorrhea and chlamydia, it will not treat syphilis. Aqueous penicillin 4 million units intravenously every 4 hours for 14 days is the treatment of choice for neurosyphilis. An alternate treatment for latent syphilis in patients who are penicillin allergic is doxycycline 100 mg twice daily for 30 days. Oral corticosteroids are not indicated in this case.

Correct Answer: E Section: (none)

Explanation:

In all likelihood, this patient is presenting with a systemic inflammatory arthritis. Clearly, treatment will need to be initiated. In order to effectively and promptly treat her, you will need to understand the current state of her physiology. Therefore, basic laboratory studies including blood count, full chemistries, and urinalysis should be obtained. At this point, the most likely diagnosis is RA, and the rheumatoid factor and sedimentation rate may be helpful. Theoretically, sarcoidosis can present in this way but, epidemiologically, this is much less likely. Because of this and because the ACE level is fairly nonspecific, it should not be part of the initial workup. Neither joint fluid aspiration nor uric acid levels are likely to be diagnostic. The elevation of serum transaminase in the face of elevated sedimentation rate, moderate or low positive ANA, and rheumatoid factors raise the question about hepatitis C.

About 50% of patients with active hepatitis C will have cryoglobulinemia. Cryoglobulins can produce low moderate positive rheumatoid factors. Therefore, it is extremely important in this circumstance to be certain that hepatitis C is not present. With such a low positive ANA, the likelihood that this is classical Lupus is low, and double-stranded DNA antibodies are not likely to be revealing. C-reactive protein may confirm the presence of inflammation, but it won't provide additional information over the sedimentation rate. Syphilis, "the great imitator," again may occasionally have arthritis as a manifestation--but rarely without other features. The remaining studies while they might be useful later but are unlikely to be helpful as the next most important test obtained. The probable source of the patient's symptoms is RA. Osteoarthritis can produce articular swelling, but on physical examination, there is rarely bogginess in the synovium. Anti-CCP antibody is an antibody directed against the citrullinated portion of fillagen. It has the highest specificity for RA of any antibody known. It is usually present early and may predict more severe disease.

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: A Section: (none)

Explanation:

Numerous causes lead to delayed puberty. Common features of Turner syndrome include short stature, sexual infantilism, "shield" chest, "webbed" neck, high arched palate, increased carrying angle of the arms (cubitus valgus), short fourth metacarpal, and streak gonads. The diagnosis of Turner syndrome requires the presence of typical phenotypic features and the complete or partial absence of a second X chromosome. Diagnosis should be considered in individuals with primary or secondary amenorrhea and in adult women with unexplained infertility, particularly when such individuals also are short in stature. Although the FSH would be elevated in Turner syndrome, it would not differentiate among the many causes of ovarian failure. In childhood, GH therapy is standard to prevent short stature as an adult. Estrogen replacement therapy usually is required, but starting too early can compromise adult height. Estrogen usually is started from age 12 to 15 years

Correct Answer: A Section: (none)

Explanation:

Down syndrome is a trisomy of chromosome 21. It is the most common nonlethal trisomy. Patau syndrome is trisomy 13 and Edwards syndrome is trisomy 18. Turner syndrome is 45 X, a monosomy. Klinefelter syndrome is the presence of an extra X chromosome in a male resulting in 47 X-X-Y. Down syndrome is the most commonly recognized genetic cause of mental retardation. The risk of trisomy 21 is directly related to maternal age as a result of maternal nondisjunction. The risk of having a child with Down syndrome increases in a gradual, linear fashion until about age 30 and increases exponentially thereafter. Women who will be 35 years or older at the time of delivery should be offered chorionic villus sampling or secondtrimester amniocentesis. Women younger than 35 years should be offered maternal serum screening at 1618 weeks of gestation. The maternal serum markers used to screen for trisomy 21 are alpha-fetoprotein, unconjugated estriol, and hCG. The use of ultrasound to estimate gestational age improves the sensitivity and specificity of maternal serum screening.

Correct Answer: B Section: (none)

Explanation:

This patient exhibits the criteria for conduct disorder. Antisocial personality disorder can only be diagnosed in a person who is over age 18. In fact, the diagnosis of antisocial personality disorder requires evidence of conduct disorder prior to age 15 (DSM IV-TR). Children with autism, schizophrenia, and mental retardation may display aggressive or disruptive behavior, but these illnesses do not necessarily predict future conduct disorder. Patients with ADHD and learning disorders are at an increased risk of developing conduct disorder as they get older.

It is not uncommon for patients with conduct disorder to have a history of oppositional defiant disorder as a younger child. Indeed, the disorders are often thought of as being on a spectrum, with oppositional defiant disorder early on, followed by conduct disorder and eventually antisocial personality disorder. Having conduct disorder does not by itself predict panic disorder, schizoid personality disorder, or the development of schizophrenia. If left untreated, there is a significantly increased risk of developing a substance use disorder, which also predicts a worse prognosis

Correct Answer: B Section: (none)

Explanation:

The mnemonic "ABCDE" is often used to remember some of the attributes of skin lesions that would make them more suspicious for being malignancies. "A" is for asymmetry; "B" for border that is irregular or indistinct from the surrounding skin; "C" for color such as dark black or variations in colors within the same lesion; "D" for diameter greater than 6 mm, or larger than the size of a pencil eraser; "E" for elevation of lesion with surface irregularity. Of the choices in question 56, the presence of a diameter of greater than 6 mm would be considered a higher-risk attribute. Primary skin malignancies are divided into three major categories--basal cell carcinoma, squamous cell carcinoma, and melanoma. Basal cell carcinomas may grow large and be locally destructive, but they have the lowest metastatic potential of the three types of skin cancer. Basal cell carcinomas are more common in persons with fair complexions but they occur in all skin types and colors. Squamous carcinomas of the skin have a metastatic potential greater than basal cell carcinomas and less than malignant melanomas. Squamous carcinomas most commonly occur in sun-exposed areas but are also associated with other etiologies, such as human papilloma virus (HPV), and can occur anywhere on the body. Malignant melanoma has the highest metastatic potential of the primary skin malignancies. Melanoma can occur in any skin type, but is more common in skin types I and II (fair skin). Obtaining a tissue sample for pathologic studies of suspicious skin lesions is critical for diagnosis and planning of appropriate treatment of melanoma. The thickness of the lesion is an important factor in these decisions. Therefore, shave biopsy would be inappropriate for the evaluation of a pigmented lesion. Complete excisional biopsy would be preferable, or, when that is not possible, full-thickness punch biopsy is an acceptable alternative. While sun exposure is an important risk factor for all types of skin cancers, for melanomas there is some evidence that intermittent, intense sun exposure and sunburning is more of a risk than cumulative sun exposure. Actinic keratoses are sun-induced skin lesions that are considered risks for the development of squamous carcinomas. They can be treated with local destructive methods, such as cryosurgery or the topical chemotherapeutic agent 5-fluorouracil. Protection of susceptible skin from excessive sun exposure from childhood is important in reducing the risk of developing skin cancer. Precautions such as wearing broad-brimmed hats, long sleeved clothing, and avoidance of intense midday sunlight are helpful. Using chemical sunscreens with SPF of greater than 15 with frequent reapplication is also beneficial. Even "waterproof" sunscreens need to be reapplied after bathing or swimming. Awet cotton T-shirt provides very little, if any, protection from ultraviolet light exposure. Both the UV-A and UV-B rays play roles in skin damage from the sun and it is important to use sun protection products, which block both types of rays. Sun tanning booths are also considered risks for the induction of skin damage and skin cancer as they expose skin to potentially damaging ultraviolet rays.

Correct Answer: C Section: (none)

Explanation:

Hashimoto thyroiditis is a very common cause of hypothyroidism in the parts of the world where iodine levels are insufficient. The clinical picture is characterized by a gradual enlargement of the thyroid gland with autoimmune destruction. There is a great female to male predominance, with ratio of 10

20:1. Clusters of families are seen which are associated with HLA-DR5 on the major histocompatibility complex (MHC). A few cases are also characterized by HLA-DR3. The pathogenesis is attributed to cellular and humoral immunity which produces thyroid tissue injury. The morphology of the thyroid gland is characterized by typical destruction of the thyroid parenchyma with dense lymphocytic infiltrate and many secondary germinal centers. Occasional scattered Hurthle cells are also seen. Depending on the stage of the disease, extensive areas of fibrosis may also be present. The clinical course of Hashimoto thyroiditis is usually an initial period of time in which the patient may be euthyroid followed by hypothyroidism.

Correct Answer: E Section: (none)

Explanation:

Adenocarcinoma of the colon is the most common type of malignancy arising in the large intestine. Iron deficiency and microcytic anemia may be the presenting symptoms due to the bleeding from the tumor's ulceration. Alternatively, the tumor may be suspected by detention of occult fecal blood test, bowel obstruction, or through the development of hepatic enlargement secondary to metastasis. The gross appearance of this tumor is usually polypoid and ulcerated. Many ulcerating tumors involve the full circumference of the bowel and appear radiologically as an "apple core" lesion. The microscopic appearance is that of gland-forming malignant cells and usually mucin production is present. The prognosis is related to the stage of the disease. Ulcerative colitis is an inflammatory disease of uncertain etiology that has a relapsing course. Patients with ulcerative colitis have a higher than normal incidence of developing colon carcinoma, approximately 10%. Carcinoid tumors originate in the neuroendocrine cells throughout the intestinal tract. The appendix is most frequently involved, followed by the terminal ileum. On histologic examination, carcinoids are composed of uniform, round cells forming small nests or cords without encapsulation. Special stains performed show neurosecretory granules in the cytoplasm, which are positive for chromogranin, neuron-specific enolase, and other staining.