Repeated USMLE Questions Step 1- 198

A 45-year-old woman visits her physician with a complaint of pain of the wrist and hand for 6 weeks. MRI confirms the diagnosis of carpal tunnel syndrome.

What is the structure that forms the anterior wall of the carpal tunnel?

A-Skin

B-Superficial fascia

C-Palmer aponeurosis

D-Flexor retinaculum

E-Extensor retinaculum

Answer





Flexor retinaculum forms the anterior wall of the carpal tunnel. It is also known as the transverse carpal ligament.

The correct answer is D

Repeated USMLE Questions Step 1- 199

A 5-year-old boy is brought to the ER by his mother. He has fever, cough, lethargy, headache and neck pain. On examination, his temperature is 103.2 F, his neck is rigid and tender and Kernig sign is positive. CSF is clear and significant for glucose 60 mg/dL, protein 80 mg/dL, no bacteria or pus cells and lymphocytes count is 70%.

What is the most likely causative organism?

A- Echovirus

B- Neisseria Meningitidis

C- Streptococcus Bovis

D- Streptococcus Pneumonia

E- Staphylococcus Aureus

Answer






History and clinical picture suggest meningitis. CSF analysis suggests viral infection rather than bacterial. Echovirus is the only choice that most likely the causative organism in this case.

The correct answer is A

Repeated USMLE Questions Step 1- 197

A 20-year-old exchange male student from Greece presents to the office for evaluation of glucose-6-phosphate dehydrogenase deficiency. Two days ago, he noticed yellow discoloration of his conjunctiva. His family history is significant for hemolytic anemia due to glucose-6-phosphate dehydrogenase deficiency. Which of these conditions is most likely associated with hemolytic anemia?

A-Increased plasma unconjugated bilirubin

B-Increased bilirubin in urine

C-Increased urobilinogen in urine

D-Clay colored stool

E-Dark brown urine

Answer





Hemolysis of RBCs results in a large amount of bilirubin delivered to the liver. The ability of the liver to conjugate all the bilirubin to glucuronic acid fails and unconjugated bilirubin increases in the plasma causing jaundice. Unconjugated bilirubin is unlikely to pass into the urine because it is bound to albumin and has low solubility in plasma. Clay colored stool occurs due to absence of bile pigments in the colon, which is not associated with hemolytic anemia.

The correct answer is A

Repeated USMLE Questions Step 1- 196

A 32-year-old woman presents with a complaint of severe pain during menstruation. She is prescribed indomethacin.

Which is the mechanism of action of this drug to reduce her pain?

A-Interferes with the production of leukotrienes

B-Limits the production of histamine

C-Stimulates the production of prostaglandin E2

D-Inhibits the production of prostaglandin E2

E-Inhibits the production of Phospholipase A2

Answer





Indomethacin inhibits the production of E2 and F2. Hence prostaglandin E2 has direct stimulatory effect on contraction of the uterus so, in this case indomethacin reduce this patient menstrual pain by inhibition of the production of prostaglandins E2.

The correct answer is D

Repeated USMLE Questions Step 1- 195

A 23-year-old man has been treated with cimetidine (Tagamet) for 6 months.

What is the mechanism of action of this drug?

A-Adds a protective membrane to gastric mucosa

B-Blocks the secretion of hydrochloric acid

C-Neutralizes gastric acidity

D-Stimulates H2 receptors

Answer




Cimetidine blocks H2 receptor so, it blocks the secretion of hydrochloric acid. It is H2 receptor antagonist.

The correct answer is B

Repeated USMLE Questions Step 1- 194

A 62-year-old man complains of severe headache, dizziness, nausea and deterioration of vision. Workup shows a decrease in oxygen carrying capacity with no change in PO2 of arterial blood.

Which of the following is most likely responsible for this patient's symptoms?

A- Ozone

B- Carbon monoxide (CO)

C- Sulfur dioxide

D- Nitrogen

Answer







This is a typical presentation of carbon monoxide poisoning. It is characterized by decreased oxygen capacity with no change in PO2 of arterial blood. Elevated level of carboxyhemoglobin should confirm the diagnosis of CO toxicity.  Ozone toxicity leads to chest pain, cough, shortness of breath and sore throat. Sulfur dioxide toxicity is causing cough, runny nose and difficulty breathing due to swollen lungs. Nitrogen toxicity is very rare and is known as inert gas asphyxiation which is used as a suicide method.

The correct answer is B

Repeated USMLE Questions Step 1- 193

A 33-year-old woman presents to the clinic for her regular yearly physical examination. She has a long history of depression and takes fluoxetine regularly for two years.

Which amino acid is the precursor of the neurotransmitter affected by this drug?

A- Glycine

B- Glutamate

C- Methionine

D- Phenylalanine

E- Tryptophan

Answer






Fluoxetine is a selective serotonin reuptake inhibitor (SSRI).

Tryptophan is converted to serotonin by tryptophan hydroxylase.

The correct answer is E

Repeated USMLE Questions Step 1- 192

An 18 year-old student visits her physician for a routine physical examination. She has no complaints. Physical examination is unremarkable except for a mid-systolic click followed by a late systolic murmur heard at the lower left sternal border and apex. The murmur duration increases in standing and shortens with squatting. Electrocardiogram (ECG) shows no abnormalities.

Which of the following is the most likely diagnosis of this condition?

A- Mitral stenosis

B- Aortic stenosis

C- Mitral valve prolapse

D- Tricuspid regurgitation

E- Dilated cardiomyopathy

Answer






The only diagnosis that matches the described murmur is mitral valve prolapse. Patients with MVP are usually asymptomatic and only diagnosed accidently or due to progress to mitral regurgitation. Normal ECG findings support this diagnosis. Mitral valve prolapse is confirmed by echocardiography.

The correct answer is C

Repeated USMLE Questions Step 1- 191

A 36-year-old man comes to the office for evaluation of involuntary movements of his hands and feet. These movements developed gradually over the past 3 years. He is otherwise in a good health and takes no medication. He does not smoke or drink alcohol. He does not drink any caffeinated beverages or use any recreational drugs. His family noticed recent personality changes over the same period. On examination, there are abnormal involuntary movements of his hands with no certain pattern. He walks in dancing like-movements that make him almost losing his balance. Mental status examination shows abnormal low score.

What is the most likely diagnosis of this patient?

A- Parkinson's disease

B- Creutzfeldt-Jakob disease

C- Tourette's syndrome

D- Drug-induced tremors

E- Huntington's disease

Answer







Dancing-like involuntary movements with no pattern are characteristic of chorea. The patient age, gradual development of symptoms and abnormal mental status suggest Huntington’s disease.

The correct answer is E

Repeated USMLE Questions Step 1- 190

A 6-year-old boy presents with fever, malaise, cough, running nose and conjunctivitis. His past medical history indicates that he did not receive any immunizations due to his parents’ religious belief. On examination, his temperature is 102.7 F and there are white spots on a red base close to his second molar teeth. He also has non-pruritic, maculopapular rash on his face, behind his ears and spreading to his chest.

What is the most likely diagnosis?

A-Chicken pox

B-Smallpox

C-Measles

D-German measles

E-Mumps

Answer






Koplik spots in the mouth are diagnostic of measles. They are white spots on a red base and found close to second molars.

The correct answer is C

Repeated USMLE Questions Step 1- 189

Three boys are brought to the urgent care clinic complaining of fever, sore throat and itchy eyes. On examination, their temperature range from 101.2 F to 102.7 F. Their conjunctivae are red and inflamed. They are a part of a group of five kids from elementary school camp out on the lake.

Which of these is the most likely causative organism of this illness?

A-Adenovirus

B-Coxsackie virus

C-Echovirus

D-Measles

E-Rubella

Answer






Adenovirus is the most common causative organism of common cold and pink eye in children. It spreads fast on schools and camps. Other viruses rarely cause these combined symptoms.

The correct answer is A

Repeated USMLE Questions Step 1- 188

A 35 year-old woman presents with troubled vision and severe pain in her left eye. She has been diagnosed with shingles on the left side of her face and the cornea of her left eye.

Which of these nerves is the most likely affected in this patient?

A-Optic nerve

B-Oculomotor nerve

C-Trigeminal nerve

D-Facial nerve







The most likely affected nerve in this patient is the trigeminal nerve (Cr V). Infection of Varicella virus starts on the face and travels through trigeminal nerve to the cornea causing trouble of vision and severe pain.

The correct answer is C

Repeated USMLE Questions Step 1- 187

A 56 year-old man presents to the emergency room complaining of severe chest pain, nausea and excessive sweating for 30 minutes. ECG and laboratory tests confirm the diagnosis of acute myocardial infarction.

What is the most likely reason of diaphoresis in this patient?

A-Parasympathetic stimulation

B-Sympathetic stimulation

C-Decreased peripheral resistance

D-Decreased sodium and water retention

E-Elevated parathyroid hormone

Answer







Myocardial infarction especially inferior MI leads to shock. Shock results in sympathetic stimulation which leads to excessive sweating. All other options are not associated with MI.

The correct answer is B

Repeated USMLE Questions Step 1- 186

A 58-year-old woman is brought to the emergency room complaining of lightheadedness for 4 hours. She has diarrhea with loose stool for 2 days. She explains her symptoms as flu and she drinks lots of water as her neighbor advised her to avoid dehydration. Her physician told her that she should take combined solution of sodium chloride (NaCl) and glucose to prevent dehydration.

What is the mechanism of action of this mixture to improve dehydration?

A- It reduces bowel contractions and consequently improves diarrhea

B- Glucose provides energy for NaCl to increase gastric emptiness

C- The mixture helps to increase secretion of water and Na through the large intestine

D- Cotransport of glucose and NaCl across the intestinal membrane facilitates absorption of water and Na.

Answer





Glucose and NaCl cotransport is the mechanism of the sodium pump. This action facilitates absorption of water and Na through the intestinal membrane and help to relieve dehydration. Ingestion of water only causes loss of Na due the difference of osmosis in the intestinal lumen and eventually enhance dehydration.

The correct answer is D

Repeated USMLE Questions Step 1- 185

A 29-year-old man is brought to the ER by a policeman. He was driving his car under the influence of alcohol. The policeman asks the ER physician to get a sample of this patient’s gastric contents for analysis. The physician explains the procedure to him but the patient refuses to go through it.

What is the best next action?

A-Force the patient to do the procedure

B-Respect the patient’s wishes and don’t do this procedure

C-Convince the patient falsely that this procedure is part of treatment and do it

D-Inject the patient with anesthesia and do the procedure

Answer







The physician’s mission is to take care of patients under all circumstance. The physician should respect the right of any patient to refuse treatments or any other procedures. The policeman doesn’t have the authority on medical decisions and medical ethics. However, blood alcohol level should be performed without the patient’s permission.

The correct answer is B

Repeated USMLE Questions Step 1- 184

A 77-year-old man presents to the emergency room with a complaint of retention of urine. Carbachol is administered to stimulate bladder emptying.

Which of the following is a prominent side effect of carbachol?

A-Tachycardia

B-Excessive salivation

C-Dry skin

D-Dilation of the pupils

E-Delirium

Answer







Carbachol is a cholinomimetic drug which activates acetylcholine receptors so, it is considered cholinergic drug. Cholinergic drugs in general enhance excessive salivation. Stimulation of cholinergic receptors lead to constriction of the pupils, a mechanism helps in glaucoma and as a preoperative drug before cataract surgery. It is also used as stimulant for bladder emptying in cases of urinary retention. It also results in excessive sweating and slow heart rate.

The correct answer is B

Repeated USMLE Questions Step 1- 183

A 16-year-old high school student presents to the office with her mother for consultation. Her mother admits that her daughter is sad because she broke up with her friend recently. Yesterday, she tried to cut her wrist but her brother screamed and they stopped her. The girl does not make eye contact and her head is bent down through the interview. She tells the doctor that she does not want to live anymore. She refuses to answer any question and declined physical examination.

What is the most appropriate next step of management for this patient?

A- Admit to the hospital

B- Refer to the psychiatric clinic next day

C- Refer to the social worker

D- Prescribe antidepressant and follow up in a week

E- Advise family that it is a normal reaction and keep an eye on her

Answer







The role of thumb in cases of suicide attempts is hospitalization.

The correct answer is A

Repeated USMLE Questions Step 1- 182

A 31 year-old pregnant woman presents to her physician on her second trimester for a prenatal checkup. She works at a big farm. She has no concerns except for some mild swellings on her neck. On physical examination, her vital signs are within normal limits. She has mild cervical lymphadenopathy. She is prescribed an oral antibiotic but she is noncompliant. Her child is delivered with hydrocephalus and intracranial calcifications.

Which organism is the most likely responsible?

A- Toxoplasma gondii

B- Treponema pallidum

C- Trypanosoma cruzi

D- Togavirus

E- Herpes simplex virus

Answer







Toxoplasma gondii is the most likely responsible for this condition. Her age, occupation, physical examination and typical signs of hydrocephalus and intracranial calcifications in the fetus are the clues to answer this question.

The correct answer is A

Repeated USMLE Questions Step 1- 181

A 22 year-old man presents to the clinic due to excessive urination. He goes to the restroom almost every 15 minutes. His physical examination is otherwise normal.

Laboratory tests show:

Serum Na: 140 mEq/L

Urine output: 4 L/24 hours

Urine is negative for glucose and protein and no pus cells

Urine Na: 18 mEq/L

Urine osmolality: 260 mOsm/kg after 4h fluid deprivation.

What is the most likely diagnosis?

A-Diabetes mellitus

B-Diabetes insipidus

C-Psychogenic polydipsia

D-Urinary tract infection

E-Solute diuresis

Answer:







Urine deprivation test shows urine osmolality lower than 400 mOsm/kg, which is diagnostic for diabetes insipidus. It is >800 in normal person and >500 in polydipsia. Absence of glucose and pus in urine excludes DM and UTI respectively.

The correct answer is B

Repeated USMLE Questions Step 1- 180

A 72-year-old man presents to his physician for a follow up after a stroke. The physician pays more attention for the care of this patient, as he reminds him of his father who passed away 3 years ago after having a stroke.

This is an example of which one of these mechanisms?

A-Acting out

B-Displacement

C-Projection

D-Transference

E-Countertransference

Answer






This is an example of countertransference, which is redirection of the physician’s feeling toward his patient. It is opposite to transference, which is redirection of the patient’s feeling of a significant person to the physician. Other options have different definitions.

The correct answer is E