USMLE USMLE-STEP-1 Online Practice Questions and Exam Preparation

USMLE USMLE-STEP-1 Online Questions & Answers

• Question 111:

  A 17-year-old patient suffers from tonicclonic seizures. This condition has been well controlled with a regimen of phenytoin. Which of the following signs or symptoms indicates phenytoin toxicity?

  A. diplopia and abnormal gait
  B. hyperprolactinemia
  C. polydipsia and polyuria
  D. postural hypotension
  E. rigidity and tremor
  A. diplopia and abnormal gait

  ---

  Explanation

  Section: Pharmacology Diplopia, abnormal gait, and other signs of cerebellar dysfunction are important symptoms of phenytoin toxicity. Other manifestations of toxicity include gingival hyperplasia, nystagmus, and vertigo. Hyperprolactinemia (choice B) is an adverse effect of antipsychotic dopamine antagonists such as the phenothiazines; dopamine inhibits prolactin secretion by the anterior pituitary. Polydipsia and polyuria (choice C) are symptoms of diabetes insipidus. These symptoms may be produced by lithium toxicity during treatment of bipolar depression, and are not associated with phenytoin toxicity. Postural hypotension (choice D) is not an adverse effect of phenytoin but often occurs with levodopa treatment of Parkinson's disease. Rigidity and tremor (choice E) are symptoms of parkinsonism. These symptoms may be produced by dopamine antagonists such as antipsychotic agents, but are not associated with phenytoin toxicity.

• Question 112:

  Which of the following colonizes the nasopharynx and produces toxins that kill ciliated epithelial cells, causes edema locally, and induces lymphocytosis systemically?

  B. Hemophilus influenzae type b
  C. L. pneumophila
  D. N. meningitides
  E. P. aeruginosa
  A

  ---

  Explanation

  Section: Microbiology/Immunology

  B. pertussis (choice A) is a highly communicable small gram-negative coccobacillus that causes whooping cough (pertussis). It is isolated on Bordet-Gengou medium.

  B. pertussis produces a number of factors involved in the pathogenesis of the disease. Ahemeagglutinin mediates attachment of the bacteria to ciliated epithelial cells. The pertussis toxin promotes lymphocytosis, histamine sensitization, and a mechanism of action similar to cholera toxin. Atracheal exotoxin inhibits DNA synthesis in ciliated

  cells. B pertussis survives only briefly outside the human host. During the catarrhal stage, large numbers of infectious bacteria are released in respiratory secretions. It is during the paroxysmal stage that the cough develops its explosive character and the "whoop" upon inhalation. Infants are especially at risk with persistent coughing in older children and even adults. An excellent vaccine is available to control this disease. The other choices (B, C, D, and E) are also upper respiratory pathogens capable of

  causing serious disease episodes. None of them produce the toxic products that are made by B. pertussis that are directly responsible for the action on cells and symptoms observed in whooping cough.

• Question 113:

  A 78-year-old man has ankle edema, tachycardia, and shortness of breath on mild exercise. His blood pressure is 155/98. He has been diagnosed with hypertension and mild heart failure. Which of the following regimens is most appropriate for starting therapy?

  A. captopril plus dobutamine
  B. captopril plus hydralazine
  C. enalapril plus hydrochlorothiazide
  D. furosemide plus spironolactone
  E. losartan plus hydralazine
  C. enalapril plus hydrochlorothiazide

  ---

  Explanation

  Section: Pharmacology The combination of an ACE inhibitor and a diuretic is rational for this patient with hypertension and mild heart failure as both drugs are effective for both conditions. Furthermore, ACE inhibitors have been shown to slow or stop the progression of heart failure and thiazide diuretics have been shown to be among the cheapest and most effective agents for hypertension. If this combination is not sufficiently active to control the heart failure, a loop diuretic mightbe substituted for the thiazide. Dobutamine (choice A) is a parenteral drug for acute failure. Hydralazine (choices B, E) is a vasodilator that causes tachycardia and usually requires concurrent administration of a beta blocker. Use of two diuretics choice D) is probably unnecessary in this early stage of failure and is not the most effective therapy for hypertension.

• Question 114:

  An elderly resident of a nursing home fell down the front steps and subsequently became disoriented and lethargic. He is brought to the emergency room where an emergency MRI reveals that he has developed hydrocephalus due to a small hemorrhage obstructing the foramina of Monro. The foramina of Monro allow for communication between which of the following?

  A. fourth ventricle and cerebral aqueduct
  B. fourth ventricle and subarachnoid space
  C. lateral ventricles and third ventricle
  D. third ventricle and cerebral aqueduct
  E. third ventricle and fourth ventricle
  C. lateral ventricles and third ventricle

  ---

  Explanation

  Section: Anatomy The foramina of Monro form the communication between the lateral ventricles and the third ventricle. The cerebral aqueduct of Sylvius flows caudally into the fourth ventricle (choice A). The lateral foramina of Luschka and the median foramen of Magendie allow for communication between the fourth ventricle and the subarachnoid space. The third ventricle communicates posteriorly with the cerebral aqueduct of Sylvius (choice D). Thus, the third and fourth ventricle communicate by way of this cerebral aqueduct.

• Question 115:

  A 50-year-old man presents with a blood pressure of 160/100. He is to be started on hydrochlorothiazide. Which of the following is a common adverse effect of hydrochlorothiazide?

  A. atrioventricular (AV) blockade
  B. constipation
  C. drug-induced lupus erythematosus
  D. potassium wasting
  E. tachycardia
  D. potassium wasting

  ---

  Explanation

  Section: Pharmacology Because thiazides decrease the reabsorption of sodium in the distal convoluted tubule, aldosterone secretion is increased and a compensatory response is evoked that releases potassium in response to increased sodium reabsorption in the cortical collecting tubule, therefore, potassium- wasting results. Other adverse effects of thiazides include increased blood glucose, uric acid, and lipids. None of the other choices (AB, E) are adverse effects of thiazide administration.

• Question 116:

  A 28-year-old woman with no significant past medical history presents to her primary care physician complaining of a chronic productive cough with blood-tinged sputum, night sweats, low-grade fever, and a 15-lbs weight loss over the past 6 weeks. Chest x-ray reveals a cavitary lesion in the left upper lobe and a calcified left hilar lymph node. Biopsy of the left upper lobe mass would most likely demonstrate which of the following?

  A. amorphous eosinophilic material surrounded by epithelioid cells and T-lymphocytes
  B. disorganized pleomorphic and hyperchromatic cells with rare mitotic figures
  C. numerous neutrophils and necrotic debris surrounded by a fibrous capsule
  D. scattered macrophages interspersed with regenerating alveolar cells and sparse collagen deposition
  E. sheets of small, uniform basophilic cells with large nuclei and scant cytoplasm
  A. amorphous eosinophilic material surrounded by epithelioid cells and T-lymphocytes

  ---

  Explanation

  Section: Pathology and Path physiology This clinical scenario describes secondary tuberculosis (TB). Upon initial exposure to the bacillus, an individual develops primary TB, where M. tuberculosis is phagocytosed by alveolar macrophages and transported to the hilar lymph nodes. As naïve macrophages are unable to kill the mycobacterium, bacteria multiply and lyse the host cell, at which time they infect other macrophages. T-cell immunity develops after a few weeks to control the initial infection. An epithelioid-cell granulomatous inflammation occurs at the site of original parenchymal infection, which, upon healing, results in scar formation, at times with late calcification that may leave a residual lesion potentially visible on chest x- ray. This parenchymal scar in association with an enlarged (and possibly calcified) hilar lymph node is known as the Ghon complex. In approximately 9095% of immunocompetent individuals, complete healing occurs. Because M. tuberculosis may persist within macrophages for many years, reactivation may occur, although the mechanisms responsible for keeping the bacilli dormant as well as those leading to reactivation are unknown. Reactivation (or, on less frequent occasions, reinfection) of TB is known as secondary TB. Typical clinical symptoms include weight loss, low-grade fever, and drenching night sweats. Reactivated TB has a predilection for the upper lung zones, presumably due to the greater availability of oxygen in this area, which enhances multiplication of the aerobic bacilli. An enhanced delayed hypersensitivity reaction results in an amplified local inflammatory response with extensive caseous necrosis. Multiple, small granulomas coalesce to form a large solid mass of fibrocaseous granulomatous inflammation known as a tuberculoma. Caseous necrosis undergoes liquefaction, and with extension of disease may erode into a bronchus, which leads to cavitation of the tuberculoma and coughing up of infectious, potentially bloody sputum. Microscopically, granulomatous inflammation is demonstrated by a central area of amorphous, eosinophilic material surrounded by epithelioid cells, frequently with Langhans-type giant cells, and an outer rim of predominantly T-lymphocytes. Disorganized pleomorphic and hyperchromatic cells with rare mitotic figures (choice B) is a generic description for lung carcinoma. Numerous neutrophils and necrotic debris surrounded by a fibrous capsule (choice C) would be suggestive of a chronic abscess, while scattered macrophages interspersed with regenerating alveolar cells and sparse collagen deposition (choice D) would occur following a necrotizing lung infection (e.g., S. aureus). Sheets of small, uniform basophilic cells with large nuclei and scant cytoplasm (choice E) is the morphological description of undifferentiated small cell (oat cell) lung carcinoma.

• Question 117:

  A 57-year-old female patient has suffered a major stroke and as a result is in a coma. The attending neurologist is very concerned because the patient is developing ataxic breathing. The pneumotaxic center and apneustic centers of the brain are located in which of the following?

  A. diencephalon
  B. midbrain
  C. pons
  D. spinal cord
  E. telencephalon
  C. pons

  ---

  Explanation

  Section: Anatomy The pneumotaxic center is located in the upper one-third of the pons, whereas the apneustic center is in the lower two-thirds. The apneustic center promotes inspiration and the pneumotaxic center, expiration. The telencephalon (choice E), diencephalon (choice A), midbrain (choice B), and spinal cord (choice D) are not known to contain pneumotaxic or apneustic centers.

• Question 118:

  A 62-year-old patient diagnosed with prostate carcinoma complains of a right-sided headache worsening over 4 days and displays a drooping right upper eyelid. Examination reveals a right third nerve palsy. An MRI reveals a single metastasis of the prostatic carcinoma in the right side of the midbrain, causing Benedikt's syndrome. Which of the following signs would also be seen in this patient?

  A. complete paralysis of facial expression musculature on the left side
  B. deviation of the tongue to the right
  C. intention tremor in the left upper and lower extremity
  D. ipsilateral hemiplegia
  E. vertical gaze palsy
  C. intention tremor in the left upper and lower extremity

  ---

  Explanation

  Section: Anatomy Benedikt's syndrome results from a lesion situated in the tegmentum of the midbrain, at the level of the third cranial nerve (oculomotor) nucleus and its associated tracts, as exemplified by ptosis and third nerve palsy in this patient. The red nucleus is also affected at this level giving rise to motor impairment displayed by the intention tremor. Since the rubrospinal tract crosses at the level of the midbrain to project to the opposite side of the body, the tremor will manifest itself contralateral to the side to the lesion. The seventh cranial nerve (facial) nucleus is located in the pons, and the facial musculature (choice A) in this patient would not be affected. Likewise, the twelfth cranial nerve (hypoglossal) nucleus is located in the medulla, and the innervation of the tongue (choice B) would be spared in this patient. A lesion causing a pure Benedikt's syndrome would be confined to the midbrain tegmentum and not affect the corticospinal tract. Ipsilateral hemiplegia (choice D) would not be present in this patient.

  Finally, vertical gaze palsy (choice E) results from a lesion or compression of the midbrain tectum and not of the tegmentum.

• Question 119:

  During a routine dental examination of a 55-year-old man, a small, reddish, and raised lesion is noted on the posterior of the median sulcus of his tongue. The patient is referred to a surgeon who performs an excisional biopsy of the lesion. A section of the biopsy is shown in below figure. Which of the following is the most appropriate diagnosis?

  

  A. amyloidosis
  B. candidiasis
  C. inverted papilloma
  D. leukoplakia
  E. squamous cell carcinoma
  E. squamous cell carcinoma

  ---

  Explanation

  Section: Pathology and Path physiology In figure, the pleomorphism of the nuclei and the clearly invasive nature of these cells indicate the malignant nature of this lesion. Furthermore, three keratin "pearls" at the bottom of the image and the sheets of cells, many with discernable intercellular bridges (prickles), allow one to recognize this as a squamous cell carcinoma. Amyloidosis (choice A) can affect many organs including the tongue. However, amyloid would appear as acellular, eosinophilic deposits around vessels and in the parenchyma of tissues which is not seen here. Candidiasis (choice B) is commonly seen on the tongue, but is not invasive in a person with an intact immune system. Its appearance is that of pseudohyphae with yeast forms. Inverted papilloma (choice C) is a benign but locally aggressive tumor found in the nose and paranasal sinuses but not seen in the tongue. Leukoplakia (choice D) of the oral cavity appears as a white patch that cannot be scraped off and cannot be otherwise identified. This is not the gross description given for this patient.

• Question 120:

  A 7-year-old girl presents with a neck mass located at the anterolateral aspect of the neck, anterior to the sternocleidomastoid muscle. A biopsy of the lesion revealed a largely cystic mass lined by stratified squamous epithelium surrounded by an underlying dense layer of lymphoid tissue with germinal centers. Based on these findings, what is the most likely diagnosis?

  A. branchial cleft cyst
  B. granulomatous lymphadenitis
  C. Hodgkin lymphoma
  D. metastatic laryngeal carcinoma
  E. thyroglossal duct cyst
  A. branchial cleft cyst

  ---

  Explanation

  Section: Pathology and Path physiology A cystic structure in the lateral neck lined by squamous or, less usually, columnar epithelium and surrounded by lymphoid issue with germinal centers is invariably a branchial cleft cyst. Granulomatous lymphadenitis (choice B) should demonstrate granulomatous inflammation in a lymph node which is not described here. Hodgkin lymphoma (choice C) occurs in five subtypes, none of which is associated with epithelial tissue. Metastatic laryngeal carcinoma (choice D) is usually squamous cell in origin and would demonstrate pleomorphic polygonal cells with "prickles" and "pearls." A thyroglossal duct cyst (choice E) can have a histological appearance very similar to that of a branchial cleft cyst but the most important difference is the midline location of the thyroglossal duct cyst.