A 4-year-old child with acute lymphoblastic leukemia is receiving high-dose methotrexate during interim maintenance. He receives ondansetron and арретitant during his stay, which control his nausea and vomiting well. These medications work by inhibiting signaling in which part of the brain?

Correct Answer: E

Rationale: The correct answer is D) Vomiting center. Ondansetron and aprepitant are antiemetic medications commonly used to control nausea and vomiting induced by chemotherapy. These medications work by inhibiting signaling in the vomiting center, which is located in the medulla oblongata of the brainstem. The vomiting center integrates signals from various areas of the body, including the chemoreceptor trigger zone, to induce the act of vomiting. Option A) Vestibular system is incorrect because this system primarily helps maintain balance and spatial orientation, not control nausea and vomiting. Option B) Cerebral cortex is incorrect because it is involved in higher-order brain functions such as thinking and decision-making, not in the regulation of nausea and vomiting. Option C) Hypothalamus is incorrect as it mainly regulates basic biological processes like hunger, thirst, and body temperature, not nausea and vomiting specifically. Understanding the mechanism of action of antiemetic medications is crucial in managing chemotherapy-induced nausea and vomiting in pediatric oncology patients. By targeting the vomiting center, healthcare providers can effectively alleviate symptoms and improve the quality of life for these young patients undergoing intensive cancer treatment.

Correct Answer: B

Rationale: The correct answer is B: Fibrinogen. In this case, the child is likely suffering from Glanzmann thrombasthenia, a rare inherited platelet disorder where platelets lack the ability to bind to fibrinogen. This results in impaired platelet aggregation and clot formation, leading to bleeding tendencies. The other options (A, C, D) are not affected in Glanzmann thrombasthenia. Platelets interact normally with ADP (A), von Willebrand factor (C), and Platelet factor 4 (D) in this disorder.

Correct Answer: D

Rationale: The correct answer is D: Lumbar puncture and cerebrospinal fluid (CSF) analysis. In Hodgkin lymphoma staging, CNS involvement is rare at initial presentation. Therefore, routine CSF analysis is not recommended unless there are specific neurological symptoms suggestive of CNS disease. A lumbar puncture carries risks of complications and should not be performed routinely. Choices A, B, and C are appropriate for staging in Hodgkin lymphoma to evaluate for distant metastases and characterize disease extent.

Correct Answer: D

Rationale: Step 1: The patient's pain is described as burning, tingling, and shooting in her left leg, which suggests neuropathic pain. Step 2: The pain worsens with hot showers, indicating sensitivity to temperature changes, a common feature of neuropathic pain. Step 3: Gabapentin is a first-line medication for neuropathic pain, as it stabilizes nerve cells and reduces abnormal pain signaling. Step 4: Starting low and titrating upward on gabapentin dose helps minimize side effects and optimize pain relief. Step 5: Methadone (Choice A) is not the best option for neuropathic pain. Increasing immediate release oxycodone (Choice B) may lead to opioid tolerance. Amitriptyline (Choice C) may help neuropathic pain but is not as specific as gabapentin.

Correct Answer: A

Rationale: The correct answer is A: Abnormal lysosomal biogenesis. In this case, the clinical presentation of silvery hair and hypopigmented skin suggests a diagnosis of Chediak-Higashi syndrome, a rare autosomal recessive disorder affecting lysosomal function. The abnormal leukocyte count and neutrophil percentage indicate impaired immune function due to defective lysosomal biogenesis. The other choices, B: Abnormal ribosome function, C: Abnormal phagocytosis of opsonized particles, and D: Abnormal mitochondrial activity, do not align with the clinical presentation and laboratory findings of this specific case.