A 16-year-old boy is brought to the emergency department because of confusion, fatigue, and abdominal pain.  He has also experienced excessive thirst and polyuria during the last 3 weeks.  His past medical history is insignificant.  Family history is unremarkable.  Urine dipstick is positive for glucose and ketones.  Which of the following factors most likely contributed to the development of this patient’s condition?

A 30-year-old woman comes to the office due to generalized weakness and paresthesia.  Medical history is unremarkable, and she takes no medications.  The patient mentions that her blood pressure was elevated at a workplace health fair 3 months ago; she attributed it to being “stressed out” and did not take any action.  Blood pressure is 150/95 mm Hg.  Cardiac examination is normal with full and symmetric distal pulses and no pedal edema.  Laboratory evaluation shows low plasma renin activity and normal serum creatinine level.  CT scan of the abdomen reveals a solitary, hypodense, 1.5-cm right adrenal mass.  Which of the following patterns of serum electrolyte concentrations would most likely be seen in this patient?

An infant is born at 39 weeks gestation to a 26-year-old woman.  The delivery was uncomplicated, and Apgar scores were 8 and 9 at 1 and 5 minutes, respectively.  The mother had gestational diabetes during pregnancy, which was controlled by diet alone.  Physical examination of the infant shows clitoromegaly and partial fusion of the labioscrotal folds.  Cytogenetic analysis reveals a 46,XX karyotype.  Abdominal imaging shows bilateral adrenal hyperplasia.  This patient is most likely deficient for an enzyme normally responsible for which of the following reactions?

A 45-year-old woman comes to the office due to a 4-month history of headaches and blurred vision.  She takes no medications and has no other medical problems.  After the initial laboratory workup, an abdominal CT is performed that shows a 2-cm left-sided adrenal mass.  The patient undergoes an uncomplicated left-sided adrenalectomy.  Gross examination of the adrenal gland demonstrates a well-defined yellowish tumor within the cortex.  Assuming the tumor cells are functionally similar to cells from the outermost layer of the adrenal cortex, this patient would most likely have presented with which of the following additional symptoms?

A 16-year-old girl is brought to the office by her mother due to concern about excessive weight loss.  The patient has lost 4.5 kg (10 lb) over the past 2 months, but thinks she still appears overweight, and is worried about gaining weight.  She does not use tobacco, alcohol, or illicit drugs.  Her mother has hypothyroidism.  Blood pressure is 130/70 mm Hg, and pulse is 105/min and regular.  There are no orthostatic changes.  BMI is 22 kg/m².  On examination, the patient appears anxious.  The thyroid is small and without palpable nodules.  There is a fine tremor seen in the fingers when the arms are outstretched.  Deep tendon reflexes are 3+ diffusely.  The skin is warm and moist.  Laboratory results show decreased TSH, elevated free thyroxine (T4), and undetectable thyroglobulin levels.  Which of the following is most likely to be seen on thyroid biopsy of this patient?

A 54-year-old woman is evaluated for a painless thyroid nodule.  She has had no weight changes, heat or cold intolerance, hoarseness, or dyspnea.  Medical history is notable for mild hypertension, for which she takes appropriate medications.  The patient does not use tobacco or alcohol.  Physical examination shows a 3-cm, firm nodule in the right thyroid lobe and enlarged, right cervical lymph nodes.  TSH is normal, and fine-needle aspiration of the nodule shows papillary structures with nuclear atypia.  Total thyroidectomy is planned.  During the surgery, a nearby nerve is injured while ligating an artery entering the superior pole of the thyroid lobe.  Which of the following muscles is most likely to be denervated as a result of this injury?

A 34-year-old man develops excessive thirst and frequent urination while being hospitalized for multiple injuries following a motorcycle collision.  His urinary osmolality after 4 hours of water restriction is 250 mOsm/L and increases to 700 mOsm/L after administration of antidiuretic hormone.  The patient is started on an appropriate medication, and his symptoms promptly resolve.  Over the next 2 years, multiple attempts are made to wean the patient off the medication, but his symptoms would always return, necessitating the resumption of treatment.  The permanence of this patient’s condition is best explained by traumatic damage to which of the following structures?

A 30-year-old woman comes to the office due to excessive weight gain without any changes in her diet or physical activity.  She has also been feeling more tired lately and has had frequent constipation.  The patient has no prior medical problems and takes no medications.  She has been pregnant once and gave birth to a healthy infant 3 years ago.  Family history is significant for a thyroid disorder in her mother.  Blood pressure is 116/90 mm Hg and pulse is 58/min.  BMI is 28.5 kg/m².  Physical examination reveals a diffusely enlarged and nontender thyroid with no nodules.  There is delayed relaxation of deep tendon reflexes.  Her hair is thin and the skin appears dry.  Which of the following sets of laboratory findings is most likely to be seen in this patient?

A 32-year-old woman comes to the office due to neck swelling.  The patient says her neck has gradually gotten larger, and she does not like how it appears in the mirror.  She otherwise feels well and has no hoarseness, trouble swallowing, or shortness of breath.  There is no history of head and neck irradiation.  The patient has no prior medical conditions and takes no medications.  She has a sister with vitiligo.  Blood pressure is 110/60 mm Hg and pulse is 75/min.  On physical examination, the thyroid is diffusely enlarged with no palpable nodules.  There is no tracheal deviation.  Serum TSH and free thyroxine levels are normal.  Antibodies against thyroid peroxidase are present in high titers.  The antigenic target of these antibodies is involved in which of the following processes?

A 45-year-old man is evaluated for a progressively enlarging neck mass and hoarseness.  Physical examination shows an enlarged and nontender left thyroid lobe.  Fine-needle aspiration biopsy is positive for papillary thyroid cancer, and a thyroidectomy is subsequently performed.  On the second postoperative day, the patient develops tingling around the mouth and muscle cramps in his lower extremities.  Blood pressure is 120/80 mm Hg, pulse is 82/min, and respirations are 14/min.  Physical examination shows normal muscle strength and deep tendon reflexes.  Light tapping anterior to the ear elicits twitching of the lower facial muscles.  An increase in which of the following best explains this patient’s current symptoms?

Researchers studying the pathophysiology of diabetes mellitus identify a family with an inherited mutation in the insulin gene.  The mutation results in a single amino acid substitution in the proinsulin molecule.  However, affected family members are asymptomatic, and most have completely normal blood glucose levels.  Analysis of the mature insulin molecule shows that it is identical to normal human insulin.  The researchers conclude that the amino acid substitution affects a segment of proinsulin removed during post-translational processing of the protein.  The polypeptide segment containing the mutation is most likely to undergo which of the following processes within pancreatic beta cells?

A newborn boy is found to have elevated TSH and low thyroxine (T4) levels on routine newborn screening.  The patient was born vaginally to a 32-year-old, healthy woman at 39 weeks gestation.  The 5-minute Apgar score was 9.  Ultrasound of the neck reveals an ectopically located, small thyroid gland just above the hyoid bone.  Early treatment with levothyroxine is indicated primarily to prevent which of the following?

A 68-year-old woman is brought to the emergency department due to worsening lethargy.  Her family states that the patient has had headache and nausea for the past several days, and today she was confused and lethargic.  Medical history is significant for a previous ischemic stroke with no residual neurologic deficit, seizure disorder, hypertension, type 2 diabetes mellitus, and bipolar disorder.  Vital signs are within normal limits.  On physical examination, the patient is somnolent and responds to painful stimuli only.  Mucous membranes are moist and jugular venous pressure is normal.  The lungs are clear to auscultation and heart sounds are normal.  There is no extremity edema.  Laboratory evaluation reveals serum sodium of 118 mEq/L; blood urea nitrogen and serum creatinine are within normal limits.  Serum osmolality is low and urine osmolality is high.  Which of the following medications is the most likely cause of this patient’s condition?

A 44-year-old woman comes to the office due to fatigue, nausea, and weight loss for the last 3-4 months.  She also has noticed her freckles becoming darker and reports frequent dizziness upon standing.  Temperature is 36.8 C (98.2 F), blood pressure is 120/80 mm Hg when sitting and 95/65 mm Hg when standing, and pulse is 77/min.  Hyperpigmentation of the vermillion border of the lips is noted.  The remainder of the physical examination is unremarkable.  Comprehensive diagnostic workup reveals a diagnosis of idiopathic primary adrenal insufficiency.  The patient is started on hydrocortisone and fludrocortisone.  Fludrocortisone is most likely to cause which of the following effects in this patient?

A 48-year-old woman comes to the office for follow-up of type 2 diabetes mellitus.  She has had diabetes for 10 years with gradually worsening glycemic control despite taking multiple oral antidiabetic agents.  Three months ago, the patient discontinued her oral medications (except for metformin) and started a daily injection of insulin glargine; she has had multiple visits with the diabetes educator since then to review injection technique and titrate up the dose.  However, the patient reports a 4.5-kg (10-lb) weight gain since starting insulin.  She says, “I feel like I need to eat more.  If that’s how insulin is going to be, then I don’t want to continue it.”  Which of the following is the most appropriate response to this patient’s statement?

A 17-year-old girl is brought to the clinic due to irregular menses.  Menarche was at age 12 and her cycles since then have been irregular, often with multiple months between menstrual periods.  The patient also has had an increase in hair growth along her chest and face.  Temperature is 37.3 C (99.1 F), blood pressure is 110/70 mm Hg, and pulse is 80/min.  There are dark, terminal hairs above the patient’s upper lip and nodulocystic acne across her forehead.  Cardiopulmonary examination is normal.  Sexual maturity rating (Tanner stage) is 5.  Ultrasound examination of the pelvis reveals a normal uterus and ovaries.  Electrolytes are normal; other laboratory results are as follows:

Which of the following enzyme reaction steps is most likely to be disrupted in this patient?

A newborn boy who was born at 39 weeks gestation by normal vaginal delivery has a serum TSH above the normal range and serum thyroxine (T4) below the normal range for his age.  His mother has no medical conditions.  On examination, the patient’s length and weight are normal, and he has no apparent congenital malformations.  Which of the following is the most likely cause of this patient’s condition?

A 62-year-old woman comes to the office for diarrhea.  She has had 4 or 5 watery, brown stools every day for the past 6 months.  Although most episodes occur during the day, she wakes up at least once a night to defecate.  There is no associated hematochezia, melena, vomiting, or unexpected weight loss.  Medical history is significant for type 2 diabetes mellitus and hypertension.  She takes lisinopril, insulin, and metformin.  She has no recent travel or new medications.  Family history is unremarkable.  She does not drink alcohol.  Temperature is 37.4 C (99.3 F), blood pressure is 125/80 mm Hg, and pulse is 80/min.  The abdomen is nontender and nondistended.  Complete blood count, serum chemistries, and stool studies are normal.  Which of the following is the most likely cause of this patient’s diarrhea?

A 2-hour-old newborn has a blood glucose concentration of 30 mg/dL.  The patient was delivered via caesarean to a 32-year-old woman at 38 weeks gestation.  Birth weight is 4.5 kg (9 lb 14 oz).  The pregnancy was complicated by gestational diabetes treated with insulin.  However, glycemic control remained suboptimal due to maternal noncompliance with insulin treatment and poor adherence to dietary recommendations.  Examination of the neonate is unremarkable.  Which of the following is the most likely primary mechanism responsible for this patient’s low blood glucose concentration?