Recalled USMLE Questions Step 1- 3

Q1- A middle aged male represents with an edematous circular skin lesion of black eschar. Which of the following bacteria is the most likely the causative organism of this condition?

A- Bacillus anthracis

B- Pneumonitis aeruginosa

C- Staphylococcus aureus

D- Streptococcus viridans





Q2- During spermatogenesis, which type of cells enter meiosis 1 to from primary spermatocytes?

A- Primordial germ cells

B- Spermatids

C- Type A spermatocytes

D- Type B spermatocytes





Q3- Which type of bias is reflected when individuals with severe disease are uncovered because they die first?

A- Confounding bias

B- Late-look bias

C- Measurement bias

D- Selection bias





Answer

Q1- A-Bacillus anthracis

Q2- D-Type B spermatocytes

Q3- B-Late-look bias

Repeated USMLE Questions Step 1- 236

An 18 year-old man presents to the office for evaluation of multiple swellings in his neck. On examination, he has multiple large lymph nodes in his neck. Neurological examination reveals poor coordination on walking. Biopsy of lymph node is positive for lymphoma. He is diagnosed with ataxia-telangiectasia.

What is the etiology of this disorder?

A- Defective DNA repair mechanisms

B- Deletion of VHL gene on chromosome 3

C- Mutation in the NF1 gene on chromosome 17

D- Mutation in PKD1 on chromosome 16

E- Mutation in APC gene on chromosome 5

Answer




Ataxia-telangiectasia is a recessive autosomal disorder caused by defective DNA repair mechanisms. It results in weakness of immune systems which leads to multiple infections and increasing risk of cancer.

The correct answer is A

Repeated USMLE Questions Step 1- 235

A 4 year-old boy visits you in the clinic with his mother for evaluation of an increasing size of his genitalia. She tells you that her boy had aggressive behavior for the last six months. Besides progressive increase of the length of his penis, he has excessive pubic hair. On examination, his pulse is 80/min. and blood pressure is 140/92 mmHg. Other than genital findings, the rest of examination is normal. You send blood and urine samples for lab testing.

What is the most likely initial diagnosis of this boy’s condition?

A- Conn syndrome

B- C-21 hydroxylase deficiency

C- C-11 hydroxylase deficiency

D- C-17 hydroxylase deficiency

Answer






This patient has a typical presentation of C-11 hydroxylase deficiency. It is manifested as hypertension, precocious puberty and abnormal behavior. This enzyme contributes to the transformation of 11-deoxycorticosterone into corticosterone which in turn forms aldosterone and also assists in the transformation of 11-deoxycortisol into cortisol. So, deficiency of this enzyme leads to lack of cortisone and aldosterone. 11-deoxycorticosterone has the same action as aldosterone on the kidneys leading to Na and water retention which results in high blood pressure. Deficiency of cortisol leads to adrenal hyperplasia due to feedback stimulation of ACTH. Increased secretion of sex hormones leads to precocious puberty.

Conn syndrome is familial hyperaldosteronism characterized by hypertension, hypokalemia and metabolic alkalosis. Sex hormones are not affected in this disorder.

C 21-hydroxylase deficiency results also in low cortisol and aldosterone and high secretion of sex hormones. It leads to hypotension and precocious puberty due to accumulation of progesterone and its transformation into testosterone by zona reticularis.

C 17-hydroxylase enzyme stimulates the transformation of pregnenolone and progesterone into sex hormones secreted by zona reticularis. Deficiency of this enzyme leads to hypertension and delayed puberty.

The correct answer is C

Repeated USMLE Questions Step 1- 234

A 22-year-old female with a history of acquired immunodeficiency syndrome (AIDS) develops low grade fever, headache and blurred vision. Cerebrospinal fluid (CSF) testing for Cryptococcal antigen is positive.

Which of these drugs can be given orally to treat Cryptococcal meningitis?

A- Amphotericin B

B- Caspofungin

C- Fluconazole

D- Metronidazole

Answer






This is a tricky question. The ideal regimen for treating cryptococcal meningitis is IV amphotericin B followed by oral fluconazole. Caspofungin is one of the echinocandins which is used in candidiasis and is only available in IV preparations. Metronidazole is a distraction as it is not effective against Cryptococcus but it is indicated in cases of anaerobic bacterial infections.

The correct answer is C

Repeated USMLE Questions Step 1- 233

A 56- year old man presents to the clinic due to recurrent attacks of severe pain in his right big toe for the last few weeks. During the attacks, his toe becomes painful, red, warm and swollen. Significant improvement occurs after treatment with colchicine. Synovial fluid analysis is performed to confirm the diagnosis.

What is the most likely finding to confirm the diagnosis?

A- Calcium oxalate crystals

B- Calcium pyrophosphate dehydrate crystals

C- Cholesterol crystals

D- Cloudy, reddish fluid, with leucocytes’ count equal to the blood count

E- Negatively birefringent urate crystals

Answer






This is a case of gout supported by the patient complaint of recurrent inflammation of the big toe and improvement of symptoms after the use of colchicine. Acute gout is confirmed by the detection of negatively birefringent monosodium urate crystals in synovial fluid analysis. Calcium pyrophosphate dehydrate crystals are found in cases of pseudo-gout. Acute arthritis is characterized by cloudy, bloody synovial fluid with leucocytes count equal to the blood count (normally synovial fluid may contain up to 200 cells /UL white blood cells). Cholesterol crystals are seen in patients with hypercholesterolemia and rheumatoid arthritis while calcium oxalate crystals can be seen in patient with renal diseases on dialysis.

The correct answer is E

Repeated USMLE Questions Step 1- 232

A 21-year-old pregnant woman visits her physician for a prenatal visit. Ultrasonography shows neural tube defects. The patient was not compliant with her medications. Assuming that the condition is caused by deficiency of a certain nutrient, which one of these abnormalities would be seen as well?

A-Microcytic anemia

B-Macrocytic anemia

C-Macrocytic anemia with neurological signs

D-Normochromic normocytic anemia

Answer






This is most likely a case of folic acid deficiency. Folic acid is routinely administered during pregnancy to avoid complications of its deficiency which result in neural tube defects. Folic acid deficiency also leads to macrocytic anemia which is differentiated from Vitamin B deficiency macrocytic anemia in lack of neurological signs. Microcytic anemia is mainly caused by iron-deficiency and some congenital diseases while normocytic anemia occurs in general diseases and some types of hemolytic anemias.

The correct answer is B

Repeated USMLE Questions Step 1- 231

A 3-month-old baby is recognized to have a horseshoe kidney. In such case, which of the following structure is known to prevent this abnormally shaped kidney from occupying the correct position?

A- Abdominal aorta

B- Celiac trunk

C- Inferior mesenteric artery

D-Superior mesenteric artery

Answer






A horseshoe kidney is a resultant of a condition where the inferior poles of the two kidneys become fused together during development. When the kidneys start to rise from the pelvis, they will encounter the inferior mesenteric artery and thus are unable to rise to what is the normal level in the abdomen.

The correct answer is C

Repeated USMLE Questions Step 1- 230

A 45-year-old man working as a secretary visits the doctor's clinic complaining of tingling and numbness in his hands. Upon conducting a physical examination, the doctor finds that the patient also has decreased sensation in all his fingers, except for the fifth digit. Keeping these in mind, which of the following muscles is usually weakened in patients suffering from this condition?

A- Adductor pollicis

B- Dorsal interossei

C- Lumbricals

D- Opponens pollicis

Answer






The patient is suffering from carpal tunnel syndrome. This condition occurs in those who work for long hours with repetitive hand motions, such as typing on a computer. In carpal tunnel, the median nerve gets compressed, which leads to a reduced sensation on the first three as well as one-half digits. There is also a loss of strength in the thumb due to reduced strength of the opponens pollicis and the abductor pollicis brevis.

The correct answer is D

Repeated USMLE Questions Step 1- 229

A 30-year-old pregnant woman comes in for a routine examination. It is found that there is a marked increase in the uterus size at 26 and 30 weeks gestation. Her physician recommends an ultrasound, which also shows a marked increase in the level of amniotic fluid. The fetus is, however, seen to be normal in size for the gestational age.

Which of the following will be the best-suited diagnosis in this scenario?

A- Congenital heart disease

B- Duodenal atresia

C- Horseshoe kidney

D- Neural tube defect

Answer






The diagnosis that fits best is that of duodenal atresia. This is a condition where the first part of the small bowel, the duodenum, does not develop properly. The cause of this condition remains unknown. Duodenal atresia is associated with many other birth defects, as well as Down’s syndrome. Other options are not accompanied with polyhydramnios but rather with changes in the size of the fetus.

The correct answer is B

Repeated USMLE Questions Step 1- 228

Chorioretinitis is a condition in which the choroid and retina of the eye become inflamed. A butcher comes to the doctor's clinic having developed chorioretinitis. On taking history, it is found out that the patient is fond of eating raw hamburgers. The doctor conducts a Sabin-Feldman dye test, the results of which come back positive.

Which of the following is the patient likely to be infected with?

A- Giardiasis

B- Toxoplasmosis

C- Trichinosis

D- Schistosomiasis

Answer






Toxoplasmosis is the most likely cause of infection, even though all the above-listed conditions have significant clinical and epidemiologic features. Toxoplasmosis is a self-limiting and mild condition that occurs if the patient ingests Toxoplasma oocysts. The consumption of raw meat is the cause of the disease. Chronic toxoplasmosis or acute toxoplasmosis is generally associated with serious eye disease, thereby making toxoplasmosis the most likely infection.

The correct answer is B

Repeated USMLE Questions Step 1- 227

A 10-year old girl is brought to the emergency room presenting with a fever over 102F for 5 days, watery diarrhea, myalgia, diffuse erythroderma, conjunctival infection, blood pressure of 105/45 mm Hg, and a strawberry tongue. The girl is also having moderately elevated levels of hepatic transaminases.

What would be the best diagnosis for the patient?

A- Toxic epidermal necrolysis

B- Kawasaki disease

C- Toxic shock syndrome

D- Stevens-Johnson syndrome

Answer






Toxic shock syndrome is a rare and life-threatening condition that can develop as a complication of certain bacterial infections. Usually, toxic shock syndrome results from the toxins produced by Staphylococcus aureus bacteria. Major symptoms of toxic shock syndrome include a sudden high fever, diarrhea, vomiting, low blood pressure, confusion, redness of the eyes, throat, and mouth, rash on the palms and soles, seizures, etc. While mostly, toxic shock syndrome is generally associated with infected tampons left in the vagina during periods, it can also happen in children, and it is absolutely necessary that it is caught and diagnosed in a timely manner to avoid life-threatening complications.

The correct answer is C

Repeated USMLE Questions Step 1- 226

A 1-year-old child is brought to the doctor. The child is known to be having microcytic anemia. The doctor orders a hemoglobin electrophoresis, which shows a higher concentration of hemoglobin A2. Which condition is the child likely to be suffering from?

A- Sickle cell anemia

B- β-thalassemia trait

C- Lead poisoning

D- Iron deficiency

Answer






β-thalassemia or beta thalassemia trait is an inherited blood disorder that has a defective production of hemoglobin. Beta thalassemia indicates a decreased production of hemoglobin. Children suffering from β-thalassemia trait tend to present poor growth, skeletal abnormalities and severe anemia particularly during the first two years of their life.

The correct answer is B

Repeated USMLE Questions Step 1- 225

You diagnose a 30-year-old healthy man with medullary cancer of the thyroid. You also note that the patient further has hyperplasia of the parathyroid gland.

Keeping all these factors in mind, you should also investigate the possibility of what in the patient?

A- Pheochromocytoma

B- Malignant melanoma

C- Hodgkin's lymphoma

D- Nowen's tumor

Answer



Pheochromocytoma grows on the adrenal glands and secretes catecholamines. It is rare and benign tumor. Multiple Endocrine Neoplasia Type 2 is a hereditary condition associated with three types of tumors, medullary carcinoma of the thyroid, pheochromocytoma and parathyroid tumors.

The correct answer is A

Repeated USMLE Questions Step 1- 222

A 23 year-old woman was involved in a motor car accident three days ago. She was hypotensive and diagnosed with internal bleeding. She received several units of blood. Today her urine output is very low for the last six hours.  Her urinalysis showed hematuria, proteinuria, muddy brown epithelial cells and granular casts. Her lab tests also show BUN: 26 mg/dL and serum creatinine: 2.6 mg/dL.

What is the most likely diagnosis of her renal pathology?

A-Acute glomerulonephritis

B-Interstitial nephritis

C-Acute tubular necrosis

D-Traumatic avulsion of the ureter

Answer






Acute tubular necrosis (ATN) is the most likely pathology in this case. It is caused by decrease in blood volume which leads to prerenal azotemia. The most common cause of renal failure associated with prerenal azotemia is acute tubular necrosis. It is characterized by rapid decline of renal function and acute elevation of blood urea and serum creatinine. The BUN/creatinine ratio is usually normal as in this case. The muddy brown epithelial cells and granular casts are also typical in ATN. Acute glomerulonephritis is characterized by the humpy lumpy appearance under light microscope and sub epithelial humps under electron microscope. It is type III hypersensitivity forming immune complexes (antigen-antibody complexes) which deposit below the podocyte foot processes of the basement membrane of the glomeruli. It occurs mainly after streptococcal infection. Interstitial nephritis is inflammation of the kidney tissue that surrounds the tubules. It is caused mainly as a side effect of some drugs or post-infection. It is characterized by eosinophilia and eosinophiluria. Traumatic avulsion of the ureter is mainly occurs as a complication of ureteroscopy. There is no mention to any surgery or trauma of any kind in this patient’s history.

The correct answer is C

Repeated USMLE Questions Step 1- 221

A 23 year old man visits his physician for routine examination. He has a history of HIV infection for 3 months and he is compliant with his medications. He is concerned about developing AIDS.

Which of the following is the most useful test to address his concern?

A-HIV antibody test

B-HIV RT PCR

C-HIV p24 antigen

D-CD4 lymphocyte count

Answer






The most recent and accurate test to determine the progress of HIV patient to develop AIDS is HIV RT PCR. Viral load of 750,000 increases significantly the chance to develop AIDS. HIV antibody test and HIV p24 antigen are important tests to diagnose HIV infection but they have no major rule in prognosis. CD4 lymphocyte count is the most common WRONG answer. It is used to check if the patient already developed AIDS and to evaluate the most possible complications. CD4 lymphocyte count is also important to determine prophylactic treatment for susceptible opportunistic infections.

The correct answer is B

Repeated USMLE Questions Step 1- 220

A study is conducted to evaluate the action of a new oral antidiabetic drug in patients with a new onset type 2 diabetes. All patients involved in the study are informed that they would be treated with a new oral antidiabetic drug. They are divided into three groups and each group would be treated with a different dose. Drug assessment is determined based on testing serum glucose and HgA1C regularly throughout the study.

Which of the following best describes this type of study?

A- Case-control study

B- Randomized controlled trial

C- Single blind clinical trial

D- Double blind clinical trial

E- Cross sectional study

Answer





This study is randomized controlled trial in which the researcher elects a certain group of patients (new onset type 2 diabetes) and informed them about the new drug. They are divided into 3 groups randomly and each group of patients receives a certain dose. Case-control study is a retrospective observational study in which 2 groups, one group already had a certain disease or symptom and the other group is normal (control group). The above study is prospective and dealing with a group of people has the same condition without a control group. Single blind clinical trial is different from the above trial in which the groups of patients are not informed about the drug or the doses used. Double blind clinical trial is different in which both the patients and the researchers don’t know which group takes certain drug or dose. Cross sectional study is an observational study in which analysis of data collected from a population at a defined time.

The correct answer is B

Repeated USMLE Questions Step 1- 219

A 23 year old man with a history of Marfan syndrome presents to the ER complaining of sharp pain on the upper back. He is admitted to intensive care unit (ICU) for the risk of aortic dissection.

Which of the following proteins are responsible for the probable development of abdominal aortic aneurysm (AAA) in this patient?

A-Myosin and actin

B-Fibrin and actin

C-Fibrillin and elastin

D-Myosin and fibrin

Answer





Marfan syndrome is a connective tissue disorder caused by FBNI gene mutation on chromosome 15 which results in defective fibrillin. It affects bones, heart, large vessels and eyes. Patients are tall with long extremities, hypermobile joints and long tapering fingers and toes. Aortic aneurysm develops due to cystic medial necrosis of the aorta.

Myosin and actin are not directly affected in Marfan syndrome. It affects fibrillin which forms a sheath around elastin.

The correct answer is C

Repeated USMLE Questions Step 1 - 155

A 23-year-old woman presents to the clinic with a complaint of pain in her left breast since last night. She is breastfeeding her 1-week-old girl. On examination, her temperature is 99.8 F, her pulse is 88/min. and her blood pressure is 120/80. Local examination of the left breast reveals a localized soft tender 1-inch area. Her past medical, surgical and family histories are unremarkable. What is the most likely diagnosis?

A- A clogged milk duct

B- A breast abscess

C- Milk engorgement

D- Mastitis

E- Inflammatory carcinoma




Answer

This is a presentation of a clogged milk duct in which the mass is localized, tender, and not erythematous or firm. There is no fever or any signs of acute inflammation. There is also no signs or family history of cancer. Abscess occurs later if this mass is infected and no treatment applied. Milk engorgement results in generalized involvement of both breasts. A clogged milk duct is diagnosed mainly by exclusion.

The correct answer is A

Repeated USMLE Questions Step 1 - 154

A 73 year old man is brought to the emergency room for dizziness and nystagmus. Examination reveals loss of sensation on the left side of his face and the right side of his body. He has hoarseness of voice and drooping of his right eyelid. The right side of the face is drier than the left side. He is referred for CT scan on his head.

What is the site of lesion responsible for hoarseness of this patient?

A- Inferior cerebellar peduncle

B- Spinal nucleus of fifth cranial nerve

C- Nucleus Ambiguus

D- Lateral spinothalamic tract






Answer

Nucleus ambiguus contains the cell bodies of the nerves that innervate soft palate, larynx and pharynx. Lesions of the nucleus ambiguus affect one or more of nerve supply to these organs. Hoarseness of voice in this case is most probably due to defect of the innervation to the larynx caused by lesion of the nucleus ambiguus.

The correct answer is C

Repeated USMLE Questions Step 1 - 152

A 17 year-old girl visits the clinic with her mother who is concerned that her daughter had not menstruated yet and her breast had not been significantly developed. She also notes that her daughter is color blind. The girl denies any sexual relationship or using any recreational drugs. Examination reveals normally appearing girl with small non-developed breasts. There is lack of pubic hair and her vagina and cervix are not fully developed. She is 5f5in tall and weighs 130 Ib. Cardiac, chest and abdominal examinations are unremarkable.

What is the most likely initial diagnosis?

A-Androgen insensitivity disorder

B- Early pregnancy

C- Kallmann’s syndrome

D- Kartagener’s syndrome

E- Turner’s syndrome

Answer






This patient has primary amenorrhea, delayed secondary sexual development and color blindness. All these features are characteristic of Kallmann’s syndrome. It is a hereditary disorder of GnRH synthesis. Androgen sensitivity disorder is characterized by the development of breasts and female external genitalia in an XY candidate. This patient has primary amenorrhea and under-developed secondary sexual characteristics which exclude pregnancy. Kartagener’s syndrome characterized by recurrent respiratory tract infections due to lack of cilia and infertility in men due to defective sperm movement. Turner’s syndrome is characterized by amenorrhea and lack of secondary sexual characteristics. It is excluded in this case because it causes dysmorphic body shape and short stature which are not available in this case.

The correct answer is C