The physician treating the 9-year-old girl in Question 5 is surprised that a medication was not administered to this patient prior to the initiation of chemotherapy to prevent tumor lysis syndrome.
Which of the following medications might have prevented this patient’s renal failure?
Allopurinol. Tumor lysis syndrome can result in acute urate nephropathy causing acute renal failure. Allopurinol has been shown to reduce the likelihood of acute urate nephropathy. Allopurinol is a purine analog that inhibits the enzyme xanthine oxidase, which prevents the production of uric acid. In addition to its use in preventing complications of tumor lysis syndrome, allopurinol is used in the treatment of chronic gout (of note, it does not treat acute gout attacks; rather it prevents attacks). Urate oxidase therapy is largely replacing allopurinol in reducing tumor lysis syndrome complications. (A, B, D) These treatments are all effective in the treatment of hyperkalemia as they all cause an intracellular potassium shift. However, even though hyperkalemia is seen in tumor lysis syndrome, these medications will have no efficacy in lowering uric acid levels and therefore not prevent acute renal failure. In other words, these medications treat the complication (hyperkalemia); they do not prevent renal failure.
A 29-year-old woman is brought to the emergency room after falling off her third floor apartment balcony. The patient suffered blunt abdominal trauma, a right femur fracture, and a left humeral fracture. On physical examination, her blood pressure is 70/30 mmHg and her heart rate is 120 beats per minute. After the administration of 5 units of packed red blood cells, the patient reports a “pins and needles” sensation on her distal toes and around her mouth. Laboratory testing confirms a calcium level of 6.9 mg/dL and a magnesium level of 1.1 mEq/L.
Which of the following is the underlying cause of this patient’s hypocalcemia and hypomagnesemia?
Chelation of calcium by an anticoagulant component of packed red blood cells. The patient in this question is experiencing signs and symptoms of hypocalcemia and hypomagnesemia. Hypocalcemia results in paresthesia that patients often report as perioral and acral “tingling” sensations. Of note, hypocalcemia also results in hyperactive tendon reflexes and QT prolongation on ECG. Whole blood and packed red blood cells derived from whole blood contain a citrate anticoagulant that chelates serum calcium and magnesium, resulting in hypocalcemia and hypomagnesemia. (B) It is true that stored red blood cells do indeed lose intracellular potassium, but this would cause hyperkalemia. (A) The patient would likely have exhibited symptoms of hypoparathyroidism prior to her current state; furthermore, a traumatic event has never been shown to unmask hypoparathyroidism. (D) Although the patient is clearly hypovolemic, this would likely cause prerenal acute kidney injury (AKI), not intrinsic AKI.
A 38-year-old obese man presents with fatigue. The patient reports several bouts of daytime sleepiness in the past 6 months. He is accompanied by his wife who reports that he snores excessively each night, and that this is causing a strain on their relationship. On physical examination, the patient has a blood pressure of 158/92 mmHg and a BMI of 34 kg/m2 . The rest of the physical examination is unremarkable. Laboratory studies reveal the following:
Which of the following explains this patient’s laboratory abnormalities?
Hypoxemia-induced increase in erythropoietin. The patient in this question is presenting with signs and symptoms consistent with a diagnosis of obstructive sleep apnea (OSA). OSA is a disease with recurrent transient obstruction of the upper airway due to pharyngeal collapse. Patients tend to be overweight and complain of daytime sleepiness, snoring, headaches, and other symptoms suggesting hypertension. Importantly, OSA episodes create a state of hypoxemia that subsequently causes the kidneys to increase erythropoietin production. Erythropoietin in turn stimulates the creation of more RBCs causing polycythemia.
(B) This answer is consistent with a diagnosis of polycythemia vera, which is a primary cause of polycythemia (as opposed to hypoxemia, which is a secondary cause) that may also present with an increase in all blood cell lines. (C) This answer is consistent with a diagnosis of CML, which would cause leukocytosis (not seen with this patient). (D) Cobalamin (vitamin B12) deficiency causes megaloblastic anemia with hypersegmented neutrophils on peripheral blood smear.
A 24-year-old woman with a history of asthma presents with fatigue. She does not have a family history as she was adopted in Albania and came to the United States when she was born. The patient reports regular menstrual cycles and denies taking any medications. Laboratory studies reveal the following:
The patient is treated with iron supplementation and returns 8 weeks later without improvement in laboratory values.
Which of the following is the likely cause of this patient’s condition?
Point mutation in one of the b-hemoglobin genes. The patient in this question is presenting with microcytic anemia that is not responding to treatment with iron. Given her Mediterranean origin, she likely has β-thalassemia. People typically have two functional copies of the β-hemoglobin gene, but those with β-thalassemia have a point mutation in one or both of these genes (classified as minor and major, respectively). This generates reduced hemoglobin production creating a hypochromic microcytic anemia. β-thalassemia major results in severe and life-threatening anemia and the need for many blood transfusions, so this patient likely has the minor form. (A) Folic acid deficiency results in macrocytic megaloblastic anemia with hypersegmented neutrophils on peripheral blood smear. (B, C) These conditions cause a normocytic anemia, but this patient has a microcytic anemia (MCV <80 fL).
A 59-year-old man with a history of benign prostatic hyperplasia (BPH) presents with fatigue, decreased appetite, and a lump in his neck. The patient has smoked 1 to 2 packs of cigarettes per day for the past 30 years. On physical examination, a 2.5 cm firm and fixed nontender left submandibular mass is palpated. The rest of the examination is unremarkable. A complete blood count and comprehensive metabolic panel are within normal limits.
Which of the following is likely to be the underlying diagnosis?
Squamous cell carcinoma. The patient in this question has an extensive history of smoking. Given the firm and nontender submandibular mass on physical examination, he likely has squamous cell carcinoma, which causes the majority of head and neck cancers. Lymph nodes that are suggestive of malignancy are hard, unilateral, and nontender. The next step in management is lymph node biopsy. (A) In chronic smokers, squamous cell carcinoma is by far the most common head and neck cancer – definitely more common than Hodgkin lymphoma. Furthermore, a patient with Hodgkin lymphoma would likely present with generalized lymphadenopathy. (B) Infectious mononucleosis would cause a painful mass in the neck, not painless. Infectious mononucleosis usually causes lymphadenopathy in the posterior cervical lymph node chain. (D) This patient is not presenting with a thyroid nodule. Papillary thyroid cancer is the most common cause of thyroid cancer and has an excellent prognosis.
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