The USMLE Step 1 exam tests how well you can apply basic, science concepts to clinical scenarios. These sample items are standard USMLE Step 1 type questions.
Question 1
A 32-year-old construction worker arrives in the emergency department after an accident on the job. The tendon of the biceps brachii at the elbow has been severed by a laceration that extends 2 cm medially from the tendon. Which of the following structures is likely to have been injured by medial extension of the laceration?
a) Brachial artery
b) Musculocutaneous nerve
c) Profunda brachii artery
d) Radial nerve
e) Ulnar nerve
Answer and Explanation
The correct answer is A. The brachial artery is immediately medial to the tendon of the biceps brachii at the elbow. As the artery enters the forearm, it is covered by the bicipital aponeurosis, a broadening of the biceps tendon.
The musculocutaneous nerve (choice B) does not cross the elbow. The musculocutaneous nerve gives off all its muscular branches to muscles in the arm. The remainder of the nerve is then renamed the lateral cutaneous nerve of the forearm, which passes the elbow lateral to the tendon of the biceps.
The profunda brachii artery (choice C) arises from the brachial artery in the proximal part of the arm. It accompanies the radial artery in the musculospiral groove and then divides into the radial collateral artery and middle collateral artery, which cross the elbow lateral to the tendon of the biceps.
The radial nerve (choice D) lies within the musculospiral groove along the back of the humerus, then passes between the brachioradialis muscle and the brachialis muscle at the elbow, lateral to the tendon of the biceps.
The ulnar nerve (choice E) crosses the elbow posterior to the medial epicondyle of the humerus. It then passes between the two heads of the flexor carpi ulnaris and courses through the forearm deep to this muscle.
Question 2
A 52-year-old man presents to his physician after a community health screening test reveals a fasting glucose of 170 mg/dL. Physical examination is remarkable for bronze skin pigmentation, hepatomegaly, splenomegaly, and limitation of motion in the second and third metacarpophalangeal joints of both hands. A liver biopsy obtained from the patient is shown above. The man has no known history of hemolytic anemia and takes daily multivitamins without minerals. Which of the following pigments is most likely present in the man's liver?
a) Bilirubin
b) Carotene
c) Ferritin
d) Lipofuscin
e) Melanin
Answer and Explanation
The correct answer is C. This patient has hemochromatosis, an inherited abnormality of iron metabolism characterized by iron accumulation in a number of tissues; the gene is tightly linked to the HLA-A6 locus. In hemochromatosis, excess iron is deposited primarily as ferritin, which is golden-yellow. Hemochromatosis has sometimes been called "bronze diabetes" because the iron deposition in blood vessels discolors skin and damages both the pancreas and liver. Diabetes mellitus may ensue from pancreatic damage; the excess iron also produces arthropathy, hypogonadism, cirrhosis, and cardiomyopathy. Patients may complain of weakness, fatigue, loss of libido, loss of weight, or abdominal pain. Hepatomegaly, splenomegaly, and signs of cirrhosis or congestive heart failure may be present in advanced cases. Cellular accumulation of the other pigments mentioned would not be associated with diabetes, arthropathy, or hepatosplenomegaly. Accumulation of iron due to iron overloading (eg, dietary excess or multiple transfusions) is called hemosiderosis.
Bilirubin (choice A) may be deposited in peripheral tissues in jaundice.
Carotene (choice B) accumulates in skin in association with excess dietary intake.
Lipofuscin (choice D) accumulates intracellularly because of lipid peroxidation, which occurs with cellular aging.
Melanin (choice E) may appear as a brown-black pigment in normal skin or in melanoma.
Question 3
A 57-year-old woman with a history of hypertension and arthritis is referred to a rheumatologist for evaluation. A complete blood count (CBC) is normal, and a mini-chem panel shows no electrolyte abnormalities. Her erythrocyte sedimentation rate (ESR) is elevated, and an antinuclear antibody test (ANA) is positive. Further antibody studies are performed, and the results are shown below.
Anti-histones: high titer
Anti-double stranded DNA: not detected
Anti-single stranded DNA: not detected
Anti-SSA: not detected
Anti-SSB: not detected
Anti-SCI-70: not detected
Anti-Smith: not detected
Anti-centromere: not detected
Anti-RNP: not detected
Which of the following diseases is suggested by these results?
a) CREST syndrome
b) Diffuse form of scleroderma
c) Drug-induced lupus
d) Sjögren syndrome
e) Systemic lupus erythematosus
Answer and Explanation
The correct answer is C. The single finding of high autoantibody titers to histones, without any other autoantibodies, is characteristic of drug-induced lupus. The most commonly implicated drugs are procainamide, hydralazine, and isoniazid. Patients typically have milder disease than in SLE and tend to have arthritis, pleuro-pericardial involvement, and, less commonly, rash. CNS and renal diseases are not usually observed.
CREST syndrome (choice A) is a milder variant of scleroderma characterized by calcinosis, Raynaud's phenomenon, esophageal dysmotility, sclerodactyly and telangiectasia. Anti-centromere antibodies are diagnostic.
The diffuse form of scleroderma (choice B), also known as systemic sclerosis, causes fibrosis of the skin and internal viscera. This disorder is characterized by anti-SCl-70 and often, low titers of many other autoantibodies.
Sjögren syndrome (choice D) is characterized by dry eyes and dry mouth. In isolated Sjögren syndrome, anti-SS-A and anti-SS-B are generally positive. If Sjögren occurs in conjunction with rheumatoid arthritis, anti-RNP will be positive as well.
Systemic lupus erythematosus (SLE; choice E) is a multisystem disorder that is distinguished from drug-induced lupus by the presence of a wide variety of autoantibodies, including anti-double stranded DNA (anti-dsDNA).