A 3-week-old boy is brought to the emergency department by his mother for fever and lethargy for 1 day. She noticed that he was moving around less than normal this morning and that he was exhibiting poor latching when she attempted to breastfeed. The patient was delivered at 39 weeks gestation via vaginal delivery, received topical erythromycin and a vitamin K injection, and had an uncomplicated postnatal course. The patient’s rectal temperature is 102.2°F (39.0°C), blood pressure is 56/32 mmHg, pulse is 180/min, and respirations are 70/min. On exam, the baby is sluggish, has a poor suck, and has dry mucous membranes. A lumbar puncture is performed with the following results: Cell count: 25/mm^3 Glucose: 22 mg/dL Protein, total: 110 mg/dL Empiric cefotaxime is started. Seven hours later, the baby is vomiting and grunting, and subcostal retractions are noted. His rectal temperature is now 104.2°F (40.1°C). What is most likely to be seen on cerebrospinal fluid (CSF) gram stain?

A 21-year-old-man presents to clinic with a depressed mood and declining academic performance. He states that he has little incentive to live, and has been having suicidal thoughts over the last few weeks, although he has not made any plans or had any attempts. He does not use illicit drugs and has no history of mania. Physical examination and laboratory values are within normal limits. The patient is diagnosed with major depressive disorder, and treatment initiation is discussed. When antidepressants are discussed, he strongly states his preference for initiating treatment. The provider is aware of data demonstrating an increased risk of suicidality in patients under 25 years old after initiating any class of antidepressants. Which of the following is the most appropriate response to the patient?

A 53-year-old man with a history of hepatitis C and cirrhosis is brought in by ambulance after his spouse noticed altered mental status that started acutely after the patient vomited blood. The patient is diaphoretic and is alert but not oriented. The patient continues to vomit blood and also complains of abdominal pain. On exam, his temperature is 98.6°F (37.0°C), blood pressure is 84/56 mmHg, pulse is 120/min, and respirations are 14/min. Resuscitation is started in the emergency department, and the patient is worked up for bleeding esophageal varices. Which of the following best explains the patient’s tachycardia?

A 56-year-old man presents to his primary care physician with a 3-year history of shortness of breath. He says that he cannot identify anything in particular that triggers his symptoms, but his symptoms have been getting worse over time. In the beginning, he had only a dry cough, but now his symptoms include chest pain, fatigue, and difficulty catching his breath after walking down his block. His past medical history is significant for type 2 diabetes, and he has worked as a welder in the aerospace industry for 30 years. Which of the following would most likely be seen on lung biopsy in this patient?

A scientist is investigating the mechanism used by a bacteria that triggers an autoimmune response in patients. She finds that the bacteria induces the production of immunoglobulin G that targets an endogenous antigen expressed by epithelial cells. These cells then get targeted by the C5b protein and are destroyed by the membrane attack complex. Which of the following proteins would be uniquely used by this pathway of complement activation?

A pharmaceutical company is developing a vaccine for COVID-19. The vaccine seeks to utilize a liposomal vector containing mRNA, with the goal of viral antigen production to be detected by the body's immune system to develop an antibody response. However, in vitro experiments demonstrate problems in the production of viral antigens. To determine the cause of this issue, new liposomes are produced that encapsulate a special form of the mRNA that is linked to a fluorescent probe. When one cell line is incubated with these liposomes and visualized with microscopy, fluorescence is observed throughout the cells' cytoplasm. No viral antigens are measurable extracellularly or in cell lysate. However, when the experiment is repeated with a different cell line, fluorescence is localized around a dense, roughly circular structure, and viral antigens are measurable extracellularly. The function of which organelle explains the difference between the 2 cell lines?

A 61-year-old man is brought to the emergency department by ambulance with a 30-minute history of chest pain. He says that he was lifting a box at work when he started feeling pain and heaviness in his chest that radiated to his left arm. During transport, he was given chewable aspirin, oxygen, and nitroglycerin. His blood pressure dropped precipitously from 113/71 mmHg to 81/49 mmHg after administration of these medications, and he was given 2L of saline for resuscitation. On presentation, his blood pressure continues to remain low at 95/51 mmHg. Elevation of the ST segment on electrocardiogram would most likely be seen in which of the following leads in this patient?

A 52-year-old man presents to his primary care physician with a 1-month history of fatigue and weakness. He says that he started noticing the symptoms when they interfered with his ability to work for prolonged periods as a plumber. He thinks that this has made him depressed and has even affected his libido. His past medical history is significant for rheumatoid arthritis, for which he takes methotrexate and prednisone. He says that the dose of prednisone was recently significantly increased due to a flare-up of the disease. Physical exam reveals the finding shown in Figure A. Which of the sets of corticotropin-releasing hormone (CRH) and adrenocorticotropic hormone (ACTH) levels in Figure B would most likely be seen in this patient?

A 70-year-old man is brought to the operating room for an emergent anterior cervical decompression and fusion following a mechanical fall. He states that he was changing his kitchen light bulbs, but lost balance from his ladder and fell four feet onto the back of his head. He denies use of any antiplatelet or anticoagulant agents. Imaging reveals no intra or extracranial bleeding. Following an uneventful operation, he is admitted to the intensive care unit intubated in a cervical collar. The patient is extubated 6 hours later. 2 hours after extubation, the patient complains of difficulty breathing while on high flow nasal cannula. His cervical collar is still in place. His respiratory rate is 30 per minute, oxygen saturation is 95%. The remainder of his vital signs are unchanged postoperatively. The patient cannot easily open his mouth. He wheezes during both inspiration and expiration. The neck drainage tubes show minimal serosanguinous output. His face mask is connected to the ventilator and reveals the image in Figure A. What is the next best step in management?

A 19-year-old woman presents to her dermatologist for evaluation of cystic acne. She was last seen 3 months ago, at which time she was initiated on doxycycline after previously trying topical benzoyl peroxide and tretinoin without significant improvement. She reports that her acne has minimally improved since then. She states that the worsening of her acne does not seem to correlate with her menstrual cycle. She has no other past medical history and takes no other medications. Her temperature is 100.1°F (37.8°C), blood pressure is 110/80 mmHg, pulse is 94/min, respirations are 12/min, and oxygen saturation is 98% on room air. On physical exam, innumerable nodules and cysts are visualized on the face and upper back. There is evidence of scarring. Which of the following is the most appropriate next step in management?

A researcher is studying opportunistic infections in patients with human immunodeficiency virus (HIV) infection. She isolates a sample from a patient with an opportunistic infection from an organism found in pigeon droppings. Figure A shows India ink staining of the sample. A latex agglutination test detects a polysaccharide capsular antigen. Which of the following organs is most likely to be affected by this organism?

A 23-year-old man presents to clinic to establish care. He is otherwise healthy and cannot recall his past surgical history, but reports having undergone an open abdominal operation a few years ago after a motor vehicle collision. He does not smoke cigarettes, drink alcohol, or use other drugs. On exam, his temperature is 36.8°C (98.2°F), blood pressure is 119/77 mmHg, pulse is 83/min, respirations are 12/min, and oxygen saturation is 100% on room air. Routine blood work shows a hemoglobin of 11 g/dL which prompts a peripheral smear, revealing the finding shown in Figure A. Which of the following is the most likely explanation for this finding?

A 3-year-old boy is brought to a primary care physician to establish care after recently immigrating to the United States. He currently has no clinical complaints, but his parents are concerned about a problem with the appearance of his upper lip. Per his parents, he has had no major illness and had not needed any surgeries. He does not take any medications and has not received any vaccinations. His temperature is 99.1°F (37.3°C), blood pressure is 110/50 mmHg, pulse is 90/min, and respirations are 22/min. Figure A is observed during physical examination. The oral cavity is unremarkable. After receiving the age-appropriate vaccinations, the patient is referred to a plastic surgeon for reconstruction. Which of the following is the underlying reason for his physical examination finding?

A 5-year-old boy presents to urgent care with a 24-hour history of a sore throat, congestion, and a runny nose in April. He also complains that his eyes have been itchy for the past month. His mother states that she was informed that several classmates in his kindergarten class have had similar symptoms, with one of his classmates having to be admitted to the hospital due to respiratory issues. The patient's vital signs show a temperature of 100.5°F (38.1°C), a blood pressure of 110/65 mmHg, a pulse of 99/min, and respirations of 17/min. On physical examination, clear breath sounds are auscultated bilaterally and rhinorrhea is observed. Mild erythema is seen on his tonsils; there are no exudates. The patient's eyes are mildly injected without evidence of discharge. Pea-sized lymph nodes are palpated along the patient's neck. Which of the following best describes the most likely pathogen?

A scientist is studying the process by which a novel toxin causes hepatotoxicity in humans. She purifies the toxin and administers it to a population of cultured hepatocytes. The next day, she finds that the cells have not divided as anticipated. Instead, she finds that all the cells have halted in the S phase of the cell cycle. She examines the genetic material in the treated hepatocytes and finds that each chromosome has at least 1 area of active DNA synthesis, but that the machinery is working much more slowly than expected. Electron microscopy reveals a strand of DNA with multiple active polymerase complexes attached to it. Which of the following best describes the newly synthesized genetic material attached to this strand?

A scientist is studying how the webbing between fingers during embryonic development is resorbed prior to birth. She models the process in cultured cells and finds that the cells demonstrate nuclear condensation and membrane blebbing after a certain point in development. She performs subcellular fractionation of these cells and discovers that there is increased activity of a protein that activates a deoxyribonucleic acid endonuclease. A protein that is encoded by which of the following genes is most likely being described in this case?

A 45-year-old woman presents to urgent care with a painful lump in her neck. The pain started 1 week ago and has worsened since then. The pain radiates to the upper neck. She also endorses myalgias and fatigue over the same time period. She had a mild non-productive cough 3 weeks ago that resolved without intervention. She has a history of hypertension for which she takes amlodipine. She does not smoke and drinks alcohol socially. The patient’s temperature is 101.3°F (38.5°C), blood pressure is 120/80 mmHg, pulse is 102/min, and respirations are 18/min. On physical examination, the physician palpates an enlarged lump in her neck that is tender to palpation and crosses the midline. An erythrocyte sedimentation rate (ESR) is found to be 60 mm/h. Which of the following sets of laboratory findings would be expected for this patient?

A 49-year-old woman presents to her physician complaining of painful sexual intercourse. Her symptoms started about 1 year ago and have worsened to the point where she avoids sex because of the pain. Three months ago, she also began having episodes of flushing of her skin in her upper chest and face, which she seems to notice especially at night. She also reports occasional sadness, low energy, and low appetite. She denies palpitations, fatigue, or skin changes. She has hypertension for which she takes hydrochlorothiazide. Her menstrual periods are irregular and she does not recall when her last one was. She does not smoke and drinks alcohol socially. The patient’s temperature is 99.6°F (37.6°C), blood pressure is 120/78 mmHg, pulse is 70/min and regular, and respirations are 16/min. Physical exam reveals a comfortable-appearing woman in no distress. Cardiovascular exam shows a normal S1 and S2 without murmurs, rubs, or gallops. Her vulvovaginal mucosa appear pale and thin. A serum prolactin level is normal. Which of the following sets of laboratory findings is most likely to be found in this patient (Figure A)?

An 81-year-old man presents to his primary care physician with a 1-month history of increasing headaches and fatigue. He says that he first started noticing the symptoms when he was trying to go for a walk with his wife, but that they have progressed to the point where he can barely leave the house. His wife also says that he seems to be more forgetful and has almost fallen several times. She also says that he has lost almost 20 pounds over the last 6 months despite no change in their diet or exercise habits. An MRI of the head is performed showing an intracranial mass that partially obstructs the ventricular system with large dilated lateral ventricles but compression of the 3rd ventricle. Where is the most likely location of the obstruction given these findings?

A 51-year-old woman presents to her gynecologist for her annual check-up. During the visit, a pap smear is performed for routine screening purposes. Based on the results of the pap smear, a biopsy is recommended with the findings shown in Figure A. Which of the following factors distinguishes this patient's condition from squamous cell cervical cancer?

A 55-year-old man is brought to the emergency department after he had a witnessed seizure at work. The seizure occurred during a work presentation and resolved without treatment. In the hospital, brain imaging reveals an enhancing lesion in the cerebral cortex that is consistent with a high-grade glioma. He is then tested for a specific change to the promoter region of a DNA repair gene that confers a favorable prognosis for this disease. Which of the following processes is most likely being assessed in this case?

A 40-year-old woman presents to her physician with urinary abnormalities. For the past 2 months, she has urinated 12-14 times per day. She states that her mouth always feels dry despite hydration. She has no difficulty with micturition and describes her urine as clear in color and normal in volume. She denies dysuria or hematuria. Her medical history consists of hypertension and major depression for which she takes chlorthalidone and bupropion. She is a non-smoker and drinks alcohol socially. She has not traveled outside of the country for the past 4 years. The patient’s temperature is 99.6°F (37.6°C), blood pressure is 124/78 mmHg, pulse is 90/min, and respirations are 16/min. Her body mass index (BMI) is 30.4 kg/m^2. Cardiopulmonary examination is unremarkable. There is no tenderness to abdominal palpation or costovertebral angle tenderness. A hemoglobin A1c level measured 2 months ago was 5.2%. A water deprivation test is performed with results shown below: Baseline: Urine osmolality: 80 mOsm/kg After water deprivation: Urine osmolality: 720 mOsm/kg Which of the following is the most likely diagnosis?

A 44-year-old man is brought to the trauma bay by an ambulance following a stab wound. He was intubated and sedated in the field due to agitation and concern for impending respiratory failure. He has no past medical history. On physical exam, his temperature is 98.6F (37°C), blood pressure is 110/80 mmHg, pulse is 102/min, respirations are 16/min, and oxygen saturation is 100%. A single 5-centimeter stab wound with well-demarcated edges is visualized on the left lateral thorax in the 5th intercostal space. Auscultation of the chest reveals distant heart sounds. Which of the following additional findings is most likely to be found in this patient?

A 35-year-old G5P5 woman presents to her gynecologist with a 1-year history of urinary incontinence. She says that she started involuntarily wetting herself soon after the birth of her last child but assumed that it would soon resolve. She is now seeking treatment because it has been embarrassing during social situations and she no longer feels comfortable going out. She denies ever wetting herself at night. Her gynecological history consists of 4 spontaneous vaginal deliveries and 1 cesarean section for fetal distress. Her temperature is 98.6°F (37°C), blood pressure is 131/86 mmHg, pulse is 81/min, and respirations are 11/min. On physical exam, she is found to lose small amounts of urine when she coughs. The vagina is well rugated without mucosal atrophy. Which of the following is the best initial treatment for this patient's condition?

A 31-year-old woman presents to her primary care physician with a 2-day history of a blister around her mouth. She says that she has recently been stressed and feels like she always gets blisters during stressful situations. She first experiences itching in the affected area and then notices redness and blister formation the next day. Her past medical history is significant only for anxiety for which she does not take any medications. Her temperature is 98.6°F (37°C), blood pressure is 113/76 mmHg, pulse is 91/min, and respirations are 13/min. Physical exam reveals the findings shown in Figure A but is otherwise unremarkable. Which of the following principles is the most likely cause of this patient's repeated symptoms?

A 78-year-old man presents to his primary care physician for his yearly wellness visit. He says that he has been feeling well overall and does not have any new complaints. His past medical history is significant for hypertension and hyperlipidemia for which he is currently taking metformin and atorvastatin. His social history is significant for a 5-pack-year history of smoking but he quit 30 years ago. His temperature is 98.6°F (37°C), blood pressure is 141/86 mmHg, pulse is 82/min, and respirations are 14/min. His body mass index is 24. Physical exam reveals no evidence of coronal or sagittal plane spinal deformity. Pulmonary exam is unremarkable. Compared to baseline results that were obtained when the patient was 50 years old, which of the sets of changes would most likely be seen in this patient's pulmonary function tests?

A 1-day-old infant is evaluated in the neonatal intensive care unit for cyanosis. He was born to a 28-year-old G1P1 woman and started to have difficulty breathing immediately upon birth. He is placed on oxygen and transferred to the intensive care unit for further evaluation. An echocardiogram is performed demonstrating the absence of a posterior interventricular septum and an aberrant tunnel structure supplied by the left anterior descending artery that connects to the aorta. This structure most likely originates from which of the following regions of the heart?

A 34-year-old man is brought to the emergency department after he was found down in a city park. He has no identifying information and the circumstances surrounding his current presentation are unknown. His temperature is 102.2°F (39.0°C), blood pressure is 102/64 mmHg, pulse is 116/min, and respirations are 14/min. A large wound is present on his left leg and he is started empirically on antibiotic treatment. One day later, he is found to be hypoxic to 83% on room air and he requires escalating respiratory support including mechanical ventilation. A chest radiograph obtained at this time is shown in Figure A. Which of the following is the most likely cause of this patient's respiratory difficulties?

A 16-year-old girl is brought to her pediatrician by her mother for a well child examination. The patient has no acute complaints or symptoms. Her medical problems consist of asthma for which she uses an albuterol inhaler as needed. She takes no other medications. She received surgery during infancy for malrotation of the intestines. She has received an up-to-date childhood vaccination series, including 1 dose of meningococcal vaccine. There is no family history of sudden cardiac death or malignancies. The patient is in the 11th grade and does well academically. After her mother is asked to leave the room, the patient states she has tried alcohol and marijuana once in the past but did not like them. She denies tobacco use. She is sexually active with her boyfriend and uses barrier contraception. She feels that over the past 6 months, she has “lost control” of her eating and eats large amounts of food quickly. She feels she “can’t stop eating” even though she feels disgusted with herself afterwards. She exercises 3 times a week for 1 hour each to lose weight. The patient’s temperature is 98.6°F (37.0°C), blood pressure is 110/60 mmHg, pulse is 90/min, and respirations are 16/min. Her body mass index is 20.9 kg/m^2. Her teeth are in good condition. Cardiopulmonary auscultation is unremarkable. There are no skin lesions on her extremities or torso. Which of the following is the most likely diagnosis?

A group of medical students are studying the effects of a new injection for the treatment of stenosing tenosynovitis. They enroll 200 patients with this disease in a randomized fashion with 100 being treated with the new injection and the others being treated with a traditional corticosteroid injection. They find that 90 of the patients treated with the new injection have complete resolution of symptoms whereas 75 of the patients treated with the corticosteroid injection have similar resolution of symptoms. Compared with corticosteroids, which of the following is the number needed to treat with the new injection?

A 45-year-old woman presents to the emergency room with a headache. The headache had an acute onset 30 minutes before admission and has not improved with ibuprofen. She has occasionally had headaches, but nothing as severe as the current episode. Her past medical history is significant for hypertension and Ehlers-Danlos syndrome. She does not drink alcohol but has smoked 2 packs of cigarettes per day for the past 25 years. Her temperature is 98.6°F (37.0°C), blood pressure is 175/95 mmHg, pulse is 115/min, respirations are 22/min, and O2 saturation is 99% on room air. A brief physical exam is notable for photophobia and nuchal rigidity. No focal neurologic deficits are noted. Computed tomography (CT) scan of the head is notable for blood in the interpeduncular, crural, ambient, and quadrigeminal cisterns. Which of the following is the most likely cause of this patient’s current presentation?

A 68-year-old man is brought to the emergency room by his wife for confusion. The patient had sudden onset of fever, headache, and myalgias 3 days before presentation. He has also had diarrhea, abdominal pain, neck pain, and photophobia. In the past day, he has been increasingly confused and weak. He has not traveled recently or been in contact with anyone sick. His past medical history is significant for obesity, hypertension, hyperlipidemia, type 2 diabetes mellitus, heart failure with preserved ejection fraction, obstructive sleep apnea, and osteoarthritis. His medications include dapagliflozin, diclofenac gel, furosemide, losartan, metformin, rosuvastatin, and tirzepatide. He drinks 1-2 beers daily and does not use tobacco. He works as a project manager for a software company, and he lives in southern California. His temperature is 101.2°F (38.4°C), blood pressure is 135/70 mmHg, pulse is 100/min, respirations are 18/min, and O2 saturation is 99% on room air. The cardiopulmonary examination is notable for regular tachycardia. He is intermittently attentive and oriented to person and place, but not to time. Neurologic examination is significant for increased tone, bradykinesia, a coarse tremor, and 3/5 strength in the lower extremities. A maculopapular rash is noted on the chest, back, and arms. A lumbar puncture is performed, which demonstrates normal opening pressure, clear cerebrospinal fluid, white blood cell count of 20/mm^3 (mostly monocytes), protein of 75 mg/dL, and a glucose of 65 mg/dL. Which of the following is the most likely cause of this patient’s symptoms?

A 35-year-old man presents to urgent care with 1 week of cough productive of brown sputum and shortness of breath. The patient has also had myalgias and fatigue. The patient has been taking his as-needed budesonide-formoterol inhaler more frequently without significant relief of symptoms. His past medical history is significant for asthma and human immunodeficiency virus (HIV) infection. His medications include both scheduled and as-needed budesonide-formoterol, as well as a bictegravir, emtricitabine, and tenofovir combination medication. He has no past surgical history. He lives in New York and works as a software engineer. He recently visited Chicago for a conference; otherwise, he has not traveled for the past 3 years. He does not drink alcohol, smoke tobacco, or use other recreational drugs. His temperature is 100.8°F (38.2°C), blood pressure is 110/65 mmHg, pulse is 80/min, respirations are 20/min, and O2 saturation is 94% on room air. Physical examination is notable for inspiratory wheezing bilaterally. Laboratory studies show: Leukocyte count: 13,000 cells/mm^3 Segmented neutrophils: 54% Bands: 3% Eosinophils: 11% Basophils: 0.5% Lymphocytes: 27% Monocytes: 5% CD4+ T-cell count: 650 cells/mm^3 Serum immunoglobulin E (IgE): 1,300 IU/mL High-resolution computed tomography (CT) scan of the chest shows widespread proximal bronchiectasis, predominantly in the upper lobes. Which of the following organisms is most likely associated with this patient’s symptoms?

A 32-year-old G2P1 woman presents to her obstetrician at 32 weeks of gestation for a routine prenatal appointment. Her pregnancy has been uncomplicated thus far. She has no complaints other than increased urinary frequency. She denies dysuria or nocturia. She records fetal kicks daily and has consistently noticed more than 10 kicks in 2 hours. Her previous child was delivered at term via spontaneous vaginal delivery. She has no past medical history including no history of diabetes or kidney disease. Her only medication is a multivitamin. Her temperature is 98.6°F (37.0°C), blood pressure is 115/70 mmHg, pulse is 85/min, respirations are 22/min, and O2 saturation is 97% on room air. Physical examination is notable for a fundal height consistent with 32 weeks of gestation, as well as a systolic ejection murmur. Fetal Doppler ultrasound shows a fetal heart rate of 150/min. A urinalysis shows: Bacteria: absent Leukocyte esterase: negative Nitrite: negative Ketones: negative White blood cells (WBC): 2 cells/HPF Red blood cells (RBC): 0-1 cells/HPF Urine epithelium: 4 cells/HPF pH: 5.5 Protein: 2+ Compared to prior to pregnancy, which of the following physiological parameters would be expected in this patient?

A 29-year-old woman presents to the emergency department with a 1-day history of itching on her leg. She says that she recently cut herself while walking in the woods but does not recall any exposures that she is aware of. She put a bandage on the cut but started experiencing itching the next morning. Her past medical history is significant for seasonal allergies and she does not currently take any medications. Her temperature is 98.6°F (37°C), blood pressure is 115/72 mmHg, pulse is 81/min, and respirations are 12/min. Oh physical exam, she is found to have a pruritic, erythematous rash under the bandage as seen in Figure A. Which of the following would be the most likely histology finding if this lesion were biopsied?