A 42-year-old woman comes to the physician because of increasing fatigue and difficulty concentrating at work for the past 2 months. She has hypertension and a 22-year history of Crohn disease. She has been hospitalized and treated for acute exacerbations involving strictures multiple times in the past. She has not had significant gastrointestinal symptoms in over a year. Current medications include mesalamine, thiazide, and bisoprolol. Her temperature is 37.2°C (99.0°F), pulse is 72/min, and blood pressure is 140/90 mm Hg. Examination shows pale conjunctivae and a soft abdomen. Rectal examination is unremarkable. Laboratory studies show:

Hemoglobin 9.4 g/dL
Mean corpuscular volume 112 μm3
Mean corpuscular hemoglobin 37.2 pg/cell
Leukocyte count 8700/mm3
Platelet count 150,000/mm3
Erythrocyte sedimentation rate 42 mm/h
Serum
Ferritin 88 ng/mL
Iron 117 μg/dL
Thyroid-stimulating hormone 3.2 μU/mL
Thyroxine 7 μg/dL
Further evaluation of this patient is most likely to show which of the following findings?

A 21-year-old man comes to the emergency room because of a 2-hour history of swelling and severe pain in his left lower leg. He has no history of serious illness or trauma. His father had a pulmonary embolism at the age of 30 years. The patient has smoked one pack of cigarettes daily for the past 3 years. He appears distressed. He is 173 cm (5 ft 8 in) tall and weighs 92 kg (203 lb); BMI is 31 kg/m2. His temperature is 37.0°C (98.6°F), pulse is 94/min, respirations are 17/min, and blood pressure is 130/78 mm Hg. Physical examination shows a tender and mildly swollen left lower leg; dorsiflexion of the left foot causes severe pain in the calf. Laboratory studies show a platelet count of 184,000/mm3, prothrombin time of 11 seconds, partial thromboplastin time of 26 seconds, and positive fibrin split products. Ultrasonography of the left leg shows incompressibility of the popliteal vein with a hyperechoic mass and absent blood flow. The patient is administered a 5000 IU intravenous bolus of unfractionated heparin followed by a constant infusion. Six hours later, the partial thromboplastin time is 28 seconds. Which of the following is the most likely underlying cause of this patient's symptoms?

A 45-year-old man comes to the physician because of a 4-day history of progressive double vision and difficulty keeping his eyes open. He says that his symptoms are present throughout the day. Two weeks ago, he was diagnosed with an upper respiratory tract infection, the symptoms of which have since resolved. He has no history of serious illness and takes no medications. He has smoked two packs of cigarettes daily for 20 years and drinks one glass of wine nightly with dinner. His temperature is 37.0°C (98.6°F), pulse is 90/min, respirations are 18/min, and blood pressure is 112/78 mm Hg. There is ptosis bilaterally and horizontal ocular movement is restricted in both eyes. Visual acuity is 20/20 bilaterally. The pupils are equal and reactive to light. Neurologic examination shows normal muscle strength, bulk, and tone. Deep tendon reflexes are absent throughout. Sensation is intact. Romberg test is positive. His gait is wide-based. Finger-to-nose and heel-to-shin testing and fundoscopic examination show no abnormalities. Which of the following is the most likely cause of this patient's symptoms?

A 14-year-old boy is brought to the physician by his mother because of a 1-month history of pain in his right leg. His mother has been giving him ketorolac at night to improve his sleep, but the pain has not improved. Physical examination shows marked tenderness along the right mid-femur. An x-ray of the right lower extremity shows several lytic lesions in the diaphysis of the femur and a surrounding cortex covered by several layers of new bone. A biopsy of the right femur shows small round blue cells. Which of the following is the most likely diagnosis?

A 54-year-old man is brought to the emergency department because of a 2-day history of progressive tingling and weakness in both legs. The patient reports that he has difficulty walking. Two weeks ago, he had bloody diarrhea and abdominal cramps that resolved spontaneously after 5 days. His vital signs are within normal limits. Examination shows weakness in the lower extremities with absent deep tendon reflexes. Reflexes are 1+ in the upper extremities. Sensation to pinprick and light touch is intact. Romberg test is negative. Laboratory studies show a leukocyte count of 12,000/mm3. Cerebrospinal fluid analysis results show:

Opening pressure normal
Protein 200 mg/dL
Glucose 70 mg/dL
White blood cells 4/mm3
This patient is at increased risk for which of the following conditions?

An exclusively breast-fed, 5-day-old boy is brought to the physician by his mother for a routine examination. He was born at term and delivery was uncomplicated. He received all standard treatment and testing prior to being discharged from the hospital 3 days ago. Examination shows no abnormalities. Without receiving additional supplementation at this time, this newborn is at greatest risk of developing which of the following conditions?