A 16 month-old girl is brought to the physician because she refused to move her older brother grabbed her right hand 1 hour ago to stop her from running into the street. On examination, she is holding the right arm in pronation. Any motion of the right elbow produces pain. There is no visible edema. Which of the following is the most likely explanation for these findings?

An 88-year-old man loses consciousness when his neck is palpated during a routine health maintenance examination. He has a 40-year history of hypertension that has been well controlled with hydrochlorothiazide and a 20-year history of degenerative osteoarthritis, for which he occasionally takes anti-inflammatory drugs. Which of the following is the most likely cause of the syncope?

A 21 -year-old woman who is a college student comes to the physician because of a severe left-sided headache, nausea, and vomiting for 1 hour. Her symptoms began with flashing lights in both eyes while she was studying for final exams. Physical examination shows no abnormalities. The most appropriate treatment is a drug that acts on a receptor for which of the following endogenous mediators?

A 56-year-old woman comes to the physician because of cough productive of blood-tinged sputum for 8 days. She also has had fatigue, loss of appetite, and an unintentional 6.8-kg (15-lb) weight loss during the past 2 months. She has a 5-year history of chronic cough and shortness of breath that she had attributed to smoking 2 packs of cigarettes daily for 42 years. She appears ill. Physical examination shows dullness to percussion over the right lower lung lobe. A chest x-ray shows a mass in the right upper lung lobe. The gross and microscopic appearances of a lung from a patient with a similar condition are shown. Which of the following is the most likely type of neoplasm in this patient?

A 3-month-old girl is brought to the physician by her mother for a well-child examination. Her mother says that the infant can lift her head when lying prone. The patient is eating well and recently started sleeping about 6 uninterrupted hours through the night. The mother adds that the baby does not yet smile in response to human faces and has not started to coo or gurgle with attention. The patient is at the 25th percentile for length and weight and 10th percentile for head circumference. Physical examination shows no other abnormalities. Which of the following best describes this infant’s development?

Two days after admission to the hospital because of a sickle cell disease crisis, a 24-year-old man suddenly develops blood in his urine and flank pain. Laboratory studies at the time of admission showed that his hematocrit was decreased to 11% from his normal baseline of 25%. Urinalysis shows gross blood, rare WBCs, and no WBC casts. Which of the following is the most likely cause of the hematuria in this patient?

A 25-year-old man who immigrated to the USA from Pakistan 2 months ago comes to the physician for a follow-up examination. He was diagnosed with hepatitis C at the age of 5 years but has had no symptoms or clinical signs of this condition. Physical examination shows no abnormalities. Serum studies done today show an AST activity of 68 U/L, ALT activity of 100 U/L, and hepatitis C virus RNA of 1.5 million lU/mL. A photomicrograph of the liver biopsy specimen is shown. Which of the following characteristic features of virus-induced histopathology is seen in this patient?

A 55-year-old homeless man comes to the emergency department because of a 2-month history of intermittent fever, cough productive of blood-tinged sputum, night sweats, and fatigue; he has had a 3.2-kg (7-lb) weight loss due to decreased appetite during this period. On arrival, he is cachectic and has a chronic cough. His temperature is 38°C (100.4°F). Rhonchi are heard over the right upper lobe. A chest x-ray shows areas of cavitation in the right upper lobe. Which of the following is the most likely cause of tissue injury in this patient’s condition?

The high therapeutic index displayed by acyclovir and its derivatives in treating herpesvirus infections is due to the fact that the drug must be activated by a viral enzyme. Which of the following enzymes is most likely being described?

A 25-year-old man is brought to the emergency department because of a 2-hour history of nausea, vomiting, abdominal cramping, and difficulty passing flatus. Examination of the face shows the lesions in the photograph; similar lesions are seen on the fingers and toes. Laboratory studies show hypochromic microcytic anemia. Test of the stool for occult blood is positive. Which of the following is the most likely diagnosis?

A 45-year-old man who is a firefighter comes to the physician because of a 3-month history of persistent cough and repeated lung infections. He has smoked 2 packs of cigarettes daily for 30 years. His respirations are 16/min. Physical examination shows dry cough and decreased lung sounds. A chest x-ray shows no abnormalities. Histologic examination of this patient’s respiratory epithelium is most likely to show which of the following types of metaplasia?

A study is conducted to assess the effectiveness of a registry for identifying patients 50 years old and older eligible for colon cancer screening. Medical practices are selected based on equal and proportional representation of both genders and socioeconomic and ethnic groups, including those who have medical insurance and those who do not. Half of the practices will use the registry for a 15-year period and the other half will provide usual care without the registry during the same period. Results show that the colon cancer mortality rate is decreased in the practices using the registry, and the researchers recommend use of a patient registry to decrease the number of deaths due to colon cancer. Which of the following study characteristics most directly supports the researchers’ recommendation?

A physician prescribes a recently marketed drug for 20 patients. After several months, five patients develop increased serum AST and ALT activities and show clinical symptoms of hepatotoxicity. The physician discontinues the drug for all patients and reports the adverse effects to the FDA. The physician has participated in which of the following phases of clinical drug testing?

An investigator is conducting a study of the effect of salt intake on renal function. The diet of an experimental animal is modified to contain only 25% of normal salt content. Which of the following is most likely to be increased in this experimental animal?

A 4-year-old boy is brought to the physician by his mother because of a 3-month history of hyperactivity and a decreased attention span. Physical examination shows no abnormalities. Laboratory studies show:

A photomicrograph of a peripheral blood smear is shown. Which of the following is the most likely underlying cause of these findings?

A 51-year-old man develops diaphoresis, tachycardia, and a blood pressure of 155/100 mm Hg 24 hours after undergoing an abdominal operation. Two hours later, he has a generalized tonic-clonic seizure. Which of the following is most likely responsible for these adverse effects in this patient?

A 36-year-old man with a 4-year history of HIV infection comes to the physician for a follow-up examination. Current medications include lopinavir-ritonavir and lamivudine (3TC)- zidovudine (AZT). His CD4 T-lymphocyte count is 410/mm3 (N>500); 6 months ago, it was 720/mm3. Reverse transcriptase polymerase chain reaction test results show that his remaining CD4 T lymphocytes are positive for CCR5. Based on the expression of CCR5, which of the following cell types in this patient is most likely also infected with HIV?

A 43-year-old man comes to the physician because of a 1-month history of chronic sinus congestion, occasional bleeding from the nose, and intermittent shortness of breath with exertion. He has had no fever or chills but has felt very “run down.” His temperature is 37.4°C (99.3°F), pulse is 88/min, respirations are 16/min, and blood pressure is 160/100 mm Hg. Physical examination shows bilateral maxillary and frontal sinus tenderness to palpation and poor transillumination. Isolated crackles are heard in the left mid lung. Cardiac examination shows no abnormalities. Laboratory studies show:

A chest x-ray shows an infiltrate in the lower segment of the left upper lobe of the lung with normal cardiac silhouette and no significant mediastinal adenopathy. A CT scan of the sinuses shows opacities bilaterally. Which of the following patterns of inflammatory vascular injury most likely underlies the pathophysiology of this patient’s disease?

One day after being admitted to the hospital for treatment of peritonitis, a 42-year-old man has progressive shortness of breath and moderate distress. Pulse oximetry on room air shows an oxygen saturation of 53%. Bilateral basilar crackles are heard on auscultation. Acute lung injury is suspected. The patient is intubated and mechanically ventilated with 90% oxygen at a lung-protective tidal volume of 550 mLand respirations of 16/min. Positive end-expiratory pressure also should be implemented to prevent which of the following complications?

A 48-year-old man comes to the physician because he is concerned about a pigmented lesion that has enlarged and changed color during the past 3 months. Physical  examination shows a 2-cm oval lesion. Histologic examination of an excisional biopsy specimen shows melanoma. If a biopsy of the lesion had been done prior to the malignant transformation, which of the following would have been the most likely diagnosis?

A 25-year-old man comes to the physician because of abdominal pain and vomiting for 1 day. He has had greasy yellow plaques on his skin and recurrent abdominal pain following ingestion of fatty meals since infancy. Physical examination shows xanthomas over the trunk and lipemia retinalis. There is tenderness over the epigastrium, and bowel sounds are decreased. Laboratory studies show leukocytosis and an increased serum amylase activity. The plasma appears milky. Which of the following is most likely increased in this patient’s serum?

A 34-year-old woman comes to the physician because of a 2-week history of easy fatigability. She is pale. Physical examination shows scleral icterus and mild jaundice. Laboratory studies show:

Which of the following is most likely responsible for the development of anemia in this patient?

A 66-year-old man is brought to the emergency department 30 minutes after the sudden onset of substernal chest pain that radiates to the neck and left arm; the pain is associated with weakness, nausea, and profuse sweating. He was jogging during the onset of pain. He has a 5-year history of hypertension treated with indapamide. His pulse is 90/min, and blood pressure is 150/90 mm Hg. Cardiac examination shows an S4. Treatment with sublingual nitroglycerin resolves his pain within 2 minutes. An ECG shows a 2-mm ST-segment elevation in the anterior leads. Treatment with a fibrinolytic drug is beneficial to this patient because of which of the following mechanisms of action?

During a study, a healthy 35-year-old woman and a 35-year-old woman with Crohn disease are given an oral solution of radiolabeled lactulose. The appearance of radioactivity in their urine is monitored over the next 24 hours. Urinary excretion of radioactivity in the patient with Crohn disease is much greater than that of the healthy subject. This finding is most likely due to inflammation-associated changes in the integrity of which of the following epithelial structures?

A 61 -year-old man has had three episodes of painless gross hematuria during the past week. The left flank is mildly tender to palpation. Urinalysis shows blood but no WBCs, bacteria, or cellular casts. He says to the physician, “Tell me like it is. Do I have cancer?” Which of the following is the most appropriate response?

A 46-year-old woman comes to the physician because of a 2-year history of progressive shortness of breath while supine; she now requires two pillows to help her sleep. She also has had a cough with occasional production of rusty-colored sputum during this period. Her respirations are 16/min. Bilateral crackles and a grade 4/6 mid-diastolic murmur are heard. Echocardiography shows left atrial dilation with mitral stenosis. No other valvular lesions are noted. The photograph shown is characteristic of her disease process. Which of the following is the most likely cause of these findings?

A 45-year-old woman comes to the physician because of a 3-week history of pain over her lateral left hip that is most severe when she awakens in the morning. She is unable to sleep on her left side due to the pain. Range of motion of the left hip is full with no pain on internal or external rotation. There is tenderness to palpation over the lateral hip. Sensation is intact. Inflammation of which of the following structures is the most likely cause of this patient’s symptoms?

A 12-year-old boy with seizure disorder is brought to the physician by his parents for a follow-up examination. His mother has two neurofibromas, and his brother and maternal uncle each have numerous cafe au lait spots. Physical examination shows numerous flat, irregular pigmented skin lesions. He is individual IV-2 in the pedigree shown. Which of the following is the most likely pattern of inheritance of this family’s disorder?

A 27-year-old woman delivers monozygotic twins at 34 weeks’ gestation. The larger twin has a hematocrit of 68%; the smaller twin is pale and has a hematocrit of 25%. Which of the following is the most likely explanation for these findings?

A 62-year-old man is brought to the physician by his wife because of increasing confusion during the past 6 months. His wife says that he has become lost twice in the past month when going to work, even though he has been going to the same office for 12 years. She adds that he often has difficulty finding objects such as his glasses and keys, sometimes cannot recall his grandchildren’s names, and has become very critical of her cooking, which he used to enjoy. When asked, he can name only the current president and none of the candidates for an upcoming presidential election, although he and his wife watch the television news together each night. Neurologic examination shows no motor or sensory abnormalities. His Mini-Mental State Examination score is 19/30. Treatment with a cholinesterase inhibitor is most likely to improve this patient’s memory because of its ability to target synaptic connections between which of the following structures?

A 12-year-old girl is brought to the physician by her mother after the dentist found many unerupted and supernumerary teeth. Physical examination shows frontal bossing, hypertelorism, and retained deciduous teeth. When prompted, the patient is able to place her shoulders together anteriorly. Serum studies show a decreased alkaline phosphatase activity. A chest x-ray shows hypoplasia of the clavicles. Skull x-rays show open sutures and multiple Wormian bones. Genetic testing shows a mutation in the CBFA1 gene. Which of the following cell types is directly affected by the mutation in this patient?

The graph shows the rate of breakdown of skeletal muscle glycogen by phosphorylase in the presence and absence of AMP. Based on the data, which of the following best describes the action of AMP?

A 60-year-old man is being evaluated for episodes of carpopedal spasm. Laboratory studies of serum show:

Which of the following conditions would most likely account for these findings?

A 32 year old man begins to laugh while eating dinner with his friends. A small particle of food irritates his pharynx and provokes him to cough. Which of the following best describes the position of his vocal cords throughout this sequence?

The table reports survival of patients who had an operation for a particular form of cancer:

Which of the following is the probability of a patient surviving 4 years?

A 3-month-old boy is brought to the physician because of yellow eyes and skin and weakness since birth. Physical examination shows jaundice, large fontanels, a flat midfacial area, hypotonia, and hepatomegaly. Serum studies show:

A liver biopsy specimen shows foamy, lipid-filled hepatocytes, necrosis, and absence of a specific organelle. This organelle is most likely which of the following?

A 27-year-old man who is a weightlifter comes to the physician for a routine examination. He has been taking a synthetic androgen for the past year to increase his muscle mass. Examination shows increased scalp hair loss and mild testicular atrophy. Which of the following is most likely responsible for the decreased size of this patient’s testicles?

A 45-year-old man is admitted to the hospital because of congestive heart failure. Two first-degree relatives died in their 40s with dilated cardiomyopathy and cirrhosis. Physical examination shows cardiac enlargement and generalized hyperpigmentation. His serum glucose concentration is 320 mg/dl_. Histologic examination of endomyocardial tissue is most likely to show an excess of which of the following?

A 45-year-old woman comes to the physician because of a 2-month history of fatigue, nausea, and generalized bone pain. She has had a 2-kg (4.4-lb) weight loss during this period because of loss of appetite. She has a 4-month history of renal insufficiency. Her blood pressure is 170/100 mm Hg. Physical examination shows pallor and 2+ pitting edema of the feet. Laboratory studies show anemia. Her serum urea nitrogen concentration is 55 mg/dL, and serum creatinine concentration is 4 mg/dL. Bone x-rays show widened osteoid seams and subperiosteal erosions. Which of the following additional sets of serum findings is most likely in this patient?

A 54-year-old woman comes to the physician because of a 10-day history of episodes of severe stabbing pain of her left cheek and jaw. She says that the pain occurs suddenly and can be precipitated by chewing, speaking, or brushing her teeth; it lasts several seconds and occurs 20 to 30 times daily. She adds, “It feels like lightning is striking my cheek.” Touching the left cheek reproduces her symptoms. Which of the following is the most likely cause of this patient’s symptoms?

A 54-year-old man comes to the physician because of a 2-week history of burning epigastric pain. He is recently divorced. His diet mainly consists of fast food. He smokes cigars and drinks one to two 12-ounce cans of beer on the weekends. He was treated for Helicobacter pylori infection 1 year ago. He uses high doses (600 mg daily) of over-the-counter ibuprofen for chronic joint pain. Abdominal examination shows tenderness to deep palpation of the epigastric area. A peptic ulcer is suspected. Which of the following is the strongest predisposing risk factor for this patient’s condition?

A 22-year-old man is brought to the physician because of a 1 -week history of bleeding gums and bruising of his legs and a 3-month history of weakness and fatigue. His temperature is 37°C (98.6°F). Physical examination shows pallor, boggy gingival hypertrophy, and several petechial lesions and ecchymoses scattered over the lower extremities. The spleen tip is palpated 3 cm below the left costal margin. Laboratory studies show:

Microscopic examination of a peripheral blood smear shows 42% blast forms. Which of the following is the most likely diagnosis?

A 20-year-old woman comes to the office because of a 1-month history of a mass in her neck. She has a 16-year history of cerebellar ataxia and progressive scleral telangiectatic lesions. Her brother has a similar condition. Physical examination shows a large, firm, nonmoveable lymph node palpable in the left anterior side of the neck. A biopsy specimen of the node shows evidence of Hodgkin lymphoma. Which of the following genetic mechanisms is the most likely cause of this patient’s lymphoma?

A 25-year-old man comes to the physician with his wife because they have been unable to conceive for 2 years. Previous examination of the wife showed no abnormalities. Examination of the patient shows no abnormalities. The patient’s laboratory studies show autoantibodies to sperm. Dysfunction of which of the following cell types is the most likely cause of these findings?

A 28-year-old woman has had restlessness, exercise intolerance, palpitations, diarrhea, and excessive sweating for the past 3 days. She had an upper respiratory tract infection 3 weeks ago. The thyroid gland is diffusely enlarged and tender. Serum total thyroxine (T4) and total triiodothyronine (T3) concentrations and free T4 index are increased. Serum thyroid-stimulating hormone concentration and radioactive iodine uptake by the thyroid gland are both decreased. Which of the following is the most likely cause of her condition?

A 25-year-old man is brought to the emergency department because of a 2-hour history of nausea, vomiting, severe abdominal pain, and shortness of breath. His respirations are 32/min. Abdominal examination shows guarding and rigidity. An x-ray of the chest and upper abdomen with the patient seated upright is shown. Based on these findings, this patient most likely has which of the following?

A 2-month-old girl is brought to the physician for a follow-up examination 2 days after a complete blood count was found to be abnormal. Her blood group is A, Rh-positive. She was born at term to a healthy 23-year-old woman whose blood group is O, Rh-positive. Birth weight was 3890 g (8 lb 9 oz). Pregnancy and delivery were uncomplicated. The patient has been active and feeding well. Her temperature is 37.6°C (99.7°F), pulse is 120/min, and respirations are 30/min. Physical examination shows no abnormalities. Laboratory studies done since birth are shown.

Which of the following is the most likely diagnosis?

A 70-year-old woman comes to the physician for a routine pelvic examination. During speculum examination of the vagina and cervix, the Valsalva maneuver causes a bulge of the anterior vaginal wall.

Which of the following is the most likely cause of this finding?

In an animal model of ischemic myocardial injury, a branch of the coronary artery is clamped. Which of the following morphologic changes is most likely to occur first?

A 16-year-old boy is brought to the emergency department 30 minutes after he dove into a 3-foot-deep swimming pool at night. On examination, he is unable to move the right upper and lower extremities. The most likely cause of the movement deficits in this patient is damage to which of the following labeled regions in the photograph of a cross section of the spinal cord shown?