Repeated USMLE Questions Step 1- 179

A 65-year-old farmer presents to the clinic for evaluation of a long time lesion on his forehead. During an examination for life insurance, the nurse noticed it and advised him to go to the clinic for evaluation. The lesion is 1.5 in diameter, tan and nodular with an adherent greasy scale. Microscopically, it shows atypical keratinocytes invading the dermis and presence of intercellular bridges between the tumor cells.

What is the most likely diagnosis?

A- Basal cell carcinoma

B- Langerhans cell histiocytosis

C- Malignant melanoma

D- Mycosis fungoides

E- Squamous cell carcinoma

Answer





This is a typical presentation of squamous cell carcinoma. Forehead is a common site due to direct exposure to sun. Gross and microscopic findings are typical for squamous cell carcinoma.

The correct answer is E

Repeated USMLE Questions Step 1- 178

A 33 year old man works at a dry cleaning service presents to his physician for a routine examination. He does not have any major health problems or significant family history. He works at his current job for 14 years. He is concerned about his daily massive exposure to carbon tetrachloride.

Which of these organs has the highest risk for damage due to this exposure?

A- Stomach

B- Small intestine

C- Heart

D- Kidney

E- Liver

Answer






Carbon tetrachloride has direct hepatotoxic effect on liver cells causing severe damage to the liver.

The correct answer is E

Repeated USMLE Questions Step 1- 177

A 27-year-old woman, who was diagnosed recently with pheochromocytoma, presents to the ER with high blood pressure. Treatment with phentolamine is initiated. Heart rate monitoring shows tachycardia after administration of her medicine.

What is the mechanism of action of phentolamine in this case?

A-Blockade of cholinergic receptors

B-Blockade of alpha-adrenergic receptors

C-Blockade of beta-adrenergic receptors

D-Direct vasoconstriction of blood vessels

E- Stimulation of adrenal gland to release epinephrine

Answer







Phentolamine is a non-selective alpha adrenergic receptor blocker. Its primary action is blocking of alpha1 receptors causing vasodilation. Because this drug is non-selective alpha blocker so, it also inhibits alpha2 receptors, which normally acts as negative feedback for epinephrine release, leading to persistent tachycardia.

The correct answer is B

Repeated USMLE Questions Step 1- 176

A 19-year-old female athlete presents to the clinic for an injury to the back of her leg. On examination, there is a bruise on the calf and the patient fails to walk on her tiptoe.

Which nerve is most likely injured?

A-Common fibular nerve

B-Superficial fibular nerve

C-Deep fibular nerve

D-Sural nerve

E-Tibial nerve

Answer:






Tibial nerve supplies the muscles in the calf, which have the main role in plantar flexion of the foot at the ankle.

Tibial and tiptoe share the tip.

The correct answer is E

Repeated USMLE Questions Step 1- 175

A 23 year-old man visits his physician for a routine examination. He is an Olympic weight lifter. He has no complaints and takes no medications. His medical, surgical and family histories are unremarkable. His muscles undergo hypertrophy and are capable of performing greater forces.

What is the reason of his muscles' hypertrophy and force?

A- Increased length of contractile fibers

B- Increased number of contractile fibers

C- Increased myosin ATPase activity

D- Increased connective tissue content

Answer:







Hypertrophy of muscles due to weight lifting is mainly caused by increased number of contractile fibers (sarcomeres) in parallel to existing units. Length of muscle fibers is limited to its origin and insertion so, it can't increase. Myosin ATPase activity will decrease due to adding more muscle fibers. Connective tissue content will not increase muscle force.

The correct answer is B

Repeated USMLE Questions Step 1- 174

A 34-year-old man newly immigrant from Kenya presents to your office for fever, sore throat and general aches. He has a long history of malaria and takes daily primaquine. Throat swab reveals streptococcal infection. You decide to prescribe an antibiotic.

Which of these antibiotics is contraindicated for this patient?

A- Ampicillin

B- Amoxicillin

C- Ciprofloxacin

D- Erythromycin

Answer:






Erythromycin blocks the metabolism of primaquine by the liver through depressing the P450 system. This leads to accumulation of primaquine causing toxicity.

The correct answer is D

Repeated USMLE Questions Step 1- 173

A 24-year-old woman visits her physician for evaluation of recurrent low grade fevers for 6 months. She has noted arthralgias and muscle fatigue and has lost about 10 pounds. She has no major health problems and she does not take any prescribed medications. She does not smoke, drink alcohol or take any recreational drugs. On examination, her temperature is 97.8 F, her pulse is 84 on her left arm and 64 on her right arm and her blood pressure is 120/70 on left arm and 106/60 on the right arm. Her laboratory tests show mild normocytic normochromic anemia, negative antineutrophil cytoplasmic autoantibody (ANCA), and slightly high erythrocyte sedimentation rate (ESR) and normal chemistry panel. Urine analysis shows normal values.

What is the most likely diagnosis?

A- Buerger disease

B- Polymyalgia rheumatica

C- Takayasu arteritis

D- Temporal arteritis

E- Systemic lupus erythematosus

Answer: 






The patient's age, low-grade fevers, weight loss, arthralgia, muscle fatigue and aortic arch involvement suggests the diagnosis of Takayasu arteritis. Buerger disease occurs mostly in smokers. Polymyalgia rheumatica and temporal arteritis occur in old age and have other criteria than Takayasu arteritis. Systemic lupus erythematosus shows different results on both serum and urine investigations.

The correct answer is C

Repeated USMLE Questions Step 1- 172

A 9-year-old boy presents to his physician with a complaint of headache, sore throat and fever. After taking history, the physician warned the parents recommending that they should never administer aspirin to the boy for the risk of having a disease that is characterized by which of the following?

A-Immunosuppression

B-Bronchospasm

C-Gastritis

D-Chronic diarrhea

E-Seizures

Answer:






Reye's syndrome is a rare side effect of aspirin especially in those who are recovering from a flu or chickenpox. It affects mainly the liver and the brain. It causes seizures and hepatomegaly. Other choices are not related to Reye's syndrome.

The correct answer is E

Repeated USMLE Questions Step 1- 171

A 38 year-old woman visits her physician complaining of palpitations, insomnia and heat intolerance. On examination, her pulse is 110/min, blood pressure is 130/80 and her temperature is 99.1 F. She has fine tremors and bulging of her eyes.

What is the most likely laboratory finding to confirm her diagnosis?

A- High serum cortisol

B- High serum thyroid stimulating hormone

C- High serum prolactin

D- Presence of thyroid-stimulating hormone receptor antibodies

E- Presence of antinuclear antibodies

Answer:







This is a typical presentation of Graves’ disease. The only laboratory test of the listed options that confirms this diagnosis is the presence of thyroid stimulating hormone receptor antibodies.

The correct answer is D

Repeated USMLE Questions Step 1- 170

Epidemic of Zika virus infection has been reported in many South American countries.

Which is the vector that transmits Zika virus to human?

A-Ticks

B-Flies

C-Rodents

D-Mosquitos

E-Stray dogs







Answer:

Mosquitos (Aedes Egypti) is the vector that transmits Zika virus to human.

The correct answer is D

Repeated USMLE Questions Step 1- 169

A 78- year-old-man who is recently diagnosed with a malignant brain tumor visits his physician with his wife to discuss his treatment options with radiotherapy and chemotherapy. When the physician explains the benefits and risks of each option, he notices that the patient does not understand everything he is saying. Meanwhile, his wife understands and asks questions. The physician knows them very well as they both share their own values and make their medical decisions together for a long time. They both agree to proceed with radiation and chemotherapy.

What is the most appropriate next step in management?

A-Start treatment immediately

B-Start treatment after obtaining a written consent from his wife

C-Refer the patient for psychiatric evaluation

D-Seek guardianship through the court

E-Schedule another appointment for the patient only to be sure of his own decision







Answer:

One of the main rules before you start any treatment is being sure that the patient understands all the benefits and risks of all treatment options. In this case, the patient cannot fully understand everything while his wife sounds comprehensive. Because you know them a long time ago and you know that her decision would be the best interest for her husband, then, you should seek a written consent from her before you start the treatment. It is important for legal reasons to have a written consent rather than oral one. There is no need for psychiatric evaluation as the patient’s ability of thought could be affected by the brain tumor. There is also no need for another appointment or guardianship as his wife is considered undisputed surrogate decision-maker.

The correct answer is B

Repeated USMLE Questions Step 1- 168

A 42-year-old African-American woman presents to the clinic because of dyspnea that worsens over the last 6 months. She has no fever, chest pain or loss of weight. The patient works as a preschool teacher. Physical examination is unremarkable. Chest x-ray shows bilateral hilar lymphadenopathy.

What is the most likely diagnosis?

A-Asbestosis

B-Pneumonia

C-Sarcoidosis

D-Tuberculosis

E-Lung cancer







Answer:

This patient has a typical presentation of sarcoidosis. She is an African American. There is dyspnea and no fever, pain or loss of weight. X-ray is also typical for sarcoidosis.

The correct answer is C

Repeated USMLE Questions Step 1- 167

A 62-year-old man presents to the clinic with rashes all over his body and painful joints. Last month, he was diagnosed with arrhythmia. He is taking one medication for it.

Laboratory tests reveal anti-histone antibodies.

Which of the following drugs is most likely responsible for this condition?

A-Hydralazine

B-Metoprolol

C-Propranolol

D-Sotalol

E-Verapamil







Answer:

This is a case of drug-induced lupus erythematosus caused by hydralazine. Other drugs do not cause DILE.

The correct answer is A

Repeated USMLE Questions Step 1- 166

A 5-year-old girl with a mass in her neck is brought to the clinic for an evaluation. Her mother says that this mass appeared 6 months ago and is increasing in size. There is no pain or discomfort. On examination, the mass is in the midline, inferior to the hyoid bone. Laboratory tests reveal normal thyroid panel. Surgery is recommended after a CT scan is performed.

What is the most likely diagnosis?

A-Dermoid cyst

B-Ectopic thyroid gland

C-Lipoma

D-Thyroglossal duct cyst

E-Branchial cleft cyst





Answer:

Normally, thyroglossal cyst disappears during development of the thyroid gland. In some cases, the duct remains in the neck and forms a cyst. It appears in the midline of the neck and is painless. Surgery is recommended to prevent infection if the CT scan shows a normal thyroid gland and thyroglossal duct cyst attached to it. All other options are possible causes but they are less common than thyroglossal duct cyst.

The correct answer is D

Repeated USMLE Questions Step 1- 165

Workers in the aniline dye industry are more susceptible to bladder cancer than general population. Meanwhile, studies show that animals, when exposed to beta-naphthylamine develop liver cancer but not bladder cancer.

What is the most likely explanation of this finding?

A-Metabolism of beta-naphthylamine by human cytochrome 450 system in the liver

B-Detoxification of beta-naphthylamine by glucuronic acid conjugation.

C-Human urinary glucuronidase splits beta-naphthylamine into glucuronic acid and a toxic metabolite.

D-Beta-naphthylamine is directly carcinogenic to human bladder







Answer:

Urinary glucourinidase is found only in human. It splits beta-nephthylamine into glucuronic acid and a toxic carcinogenic metabolite.

The correct answer is C

Repeated USMLE Questions Step 1- 164

A 33-year-old man presents to his physician to discuss his plans for treatment of hyperthyroidism. One of the options is potassium perchlorate.

What is the mechanism of action of potassium perchlorate as anti-thyroid?

A-Blocking of coupling of iodotyrosines

B-Blocking of peroxidase catalyzed reactions

C-Blocking of peripheral deiodination of T3 and T4

D-Competitive inhibition of iodide transport mechanism

E-Inhibition of the release of thyroid hormone from the thyroid gland

Answer:





Potassium perchlorate prevents the uptake of iodine by thyroid gland by competitive inhibition of iodide transport mechanism.

The correct answer is D

Repeated USMLE Questions Step 1- 163

As physicians, we need to know some definitions in Genetics, which are related directly to our practice and guide us to diagnose and treat many genetic disorders. These items include genome, genotype, phenotype, genetic code, gene expression, etc.

Which one of the following choices describes the definition of a phenotype?

A- Genetic history of an organism

B- DNA structure that determines the expression of a trait

C- An observable physical or biochemical trait on an organism

D- Physical location of a trait on a DNA molecule


Answer:






Phenotype is the observable physical or biochemical features that seen on an organism featuring the expression of genotype.

The correct answer is C

Repeated USMLE Questions Step 1- 162

A 45 year-old man presents with progressive burning epigastric pain. He smokes and drinks alcohol socially. Physical examination, laboratory tests and imaging studies confirm the diagnosis of peptic ulcer. He is prescribed omeprazole.

What is the effect of this medication that improves this condition?

A-Anti-cholinergic effect

B-Inhibition of H+/K+ ATPase pump

C-Blocking of H2 receptor

D-Neutralization of gastric acid

E-Forming a layer to protect gastric mucosa


Answer:







Administration of omeprazole leads to irreversible inhibition of the H+/K+ ATPase pump in the parietal cell membrane. Other choices are mechanisms of action of other drugs also used in peptic ulcer medical treatment.

The correct answer is B

Repeated USMLE Questions Step 1- 161

A 68 year-old man with a long history of poorly controlled diabetes presents to his physician complaining of pain and drainage in his left ear. His vital signs are within normal limits. The pinna of his left ear is tender. The external meatus is swollen and covered with purulent drainage.

What is the most likely organism responsible for his condition?

A-Candida albicans

B-Homophilus influenzae

C-Pseudomonas aeruginosa

D-Moraxella catarrhalis

E-Streptococcus pneumoniae






Answer:

This infection is most likely malignant otitis externa and caused by pseudomonas aeruginosa. It is common in elderly people and specifically those with a history of poorly controlled diabetes. Other organisms mainly cause otitis media but they very rarely affect external ear.

The correct answer is C

Repeated USMLE Questions Step 1- 160

A 74-year-old man with a long history of emphysema presents to the office for a routine examination. He is complaining of fatigue and shortness of breath for 2 weeks. Physical examination is remarkable for scattered wheezes on both lung bases. Arterial blood gas is ordered for the patient.

Which one of these results reflects the shift of oxygen dissociation curve to the right?

A- pH 7.00, bicarbonate 15, Pco2 60 and Po2 90

B- pH 7.05, bicarbonate 15, Pco2 30 and Po2 90

C- pH 7.47, bicarbonate 15, Pco2 30 and Po2 90

D- pH 7.50, bicarbonate 24, Pco2 40 and Po2 90

E- pH 7.60, bicarbonate 24, Pco2 60 and Po2 90

Answer






This patient has a long history of emphysema and respiratory distress. He exhibits respiratory acidosis due to defective gas exchange and shortness of breath. This condition is associated with shifting oxygen dissociation curve to the right. Shift to the right is caused by low pH, high Pco2 and low Po2.

The correct answer is A