WBR0543

Author	[[PageAuthor::Rim Halaby, M.D. [1]]]
Exam Type	ExamType::USMLE Step 1
Main Category	MainCategory::Pharmacology
Sub Category	SubCategory::Neurology
Prompt	[[Prompt::A 32 year old male patient who is previously healthy is brought to the emergency department (ED) in a decreased level of consciousness. His family reports he takes no medications and has no allergies. Vital signs show a temperature of 36.3 degrees C (97.4 degrees F), a heart rate of 44 bpm, a respiratory rate of 6/min, and a blood pressure measuring 100/60 mmHg. On physical examination, the patient is difficult to arouse, he has pinpoint pupils, and track marks on his arm. The physician in the ED suspects drug abuse. Which of the following corresponds to the mechanism of pupillary constriction in this patient?]]
Answer A	AnswerA::Activation of gamma-aminobutyric acid (GABA) receptors in the geniculocalcarine radiations
Answer A Explanation	AnswerAExp::Opioid receptors are activated in opioid toxicity. GABA has no role in pupillary constriction. The geniculocalcarine radiations are not responsible for pupillary constriction.
Answer B	AnswerB::Activation of opioid receptors in the Edinger-Westphal nucleus
Answer B Explanation	AnswerBExp::The activation of opioid receptors in the Edinger-Westphal nucleus is the mechanism behind pupillary constriction in opioid toxicity.
Answer C	AnswerC::Activation of glutamate receptors in the lateral geniculate nucleus
Answer C Explanation	AnswerCExp::Opioid receptors are activated in opioid toxicity. GABA has no role in pupillary constriction. The lateral geniculate nucleus is not responsible for pupillary constriction.
Answer D	AnswerD::Activation of opioid receptors in the superior colliculus
Answer D Explanation	AnswerDExp::The superior colliculus is not responsible for pupillary constriction.
Answer E	AnswerE::Activation of GABA receptors in the oculomotor nerve
Answer E Explanation	[[AnswerEExp::Opioid receptors are activated in opioid toxicity. GABA has no role in pupillary constriction. Although the oculomotor nerve is involved due to the activation of receptors in the Edinger-Westphal nucleus, the activated receptors are of opioid type not GABA.]]
Right Answer	RightAnswer::B
Explanation	[[Explanation::Opioid analgesic overdose is a life-threatening condition that affects multiple organ systems. Opioids increases the activity of G-protein-coupled transmembrane mu, delta, and kappa opioid receptors in various organs of the body. As a result, heterodimer and homodimer receptors form to activate endogenous and exogenous compounds. Patients with opioid overdose are usually in a comatose-like condition with signs of cardiopulmonary depression on physical examination (low heart rate, low respiratory rate, and low blood pressure). On physical examination, patients with chronic abuse of opioids may have visible track marks on their arms. Their ophthalmologic exam shows the characteristic finding of pinpoint pupils. Opioid receptors in the brain stem mediate the respiratory depression in patients with opioid toxicity. Pinpoint pupils occur following the activation of the opioid receptor in the Edinger-Westphal nucleus of the oculomotor nerve. Educational Objective:Opioid receptor in the Edinger-Westphal nucleus mediates the pupillary constriction in opioid toxicity. Reference: Boyer EW. Management of opioid analgesic overdose. N Eng J Med. 2012;367:146-55. Educational Objective: References: ]]
Approved	Approved::No
Keyword	WBRKeyword::opioid, WBRKeyword::toxicity, WBRKeyword::Edinger, WBRKeyword::Westphal, WBRKeyword::Edinger-westphal, WBRKeyword::edinger westphal, WBRKeyword::pupillary, WBRKeyword::constriction, WBRKeyword::pupillary constriction, WBRKeyword::morphine, WBRKeyword::drug, WBRKeyword::overdose
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