ABEM Toxicology, Environmental & Infectious Diseases 4 — Questions and Answers
Question 1: A scuba diver surfaces too quickly and develops joint pain, dyspnea, and marbling of the skin. Which chamber pressure is used in hyperbaric oxygen therapy for decompression sickness?
- 1.5 ATA
- 2.8 ATA (Correct answer)
- 3.5 ATA
- 2.0 ATA
Correct answer: 2.8 ATA
US Navy Treatment Table 6 uses 2.8 ATA with 100% oxygen to maximize bubble reabsorption and treat decompression illness.
Question 2: A 30-year-old with fever, painless ulcer on the penis, and bilateral inguinal lymphadenopathy is diagnosed with primary syphilis. He has a documented penicillin allergy with anaphylaxis. What is the recommended alternative?
- Azithromycin 1 g single dose
- Doxycycline 100 mg BID for 14 days
- Ceftriaxone 1 g IM daily for 10 days
- Desensitization followed by penicillin G benzathine (Correct answer)
Correct answer: Desensitization followed by penicillin G benzathine
Penicillin G benzathine is the only proven treatment for all stages of syphilis; in penicillin-allergic patients with primary syphilis, doxycycline is acceptable but desensitization is preferred in non-pregnant patients with neurosyphilis or pregnancy.
Question 3: A patient with fever and rigors after returning from sub-Saharan Africa has a peripheral blood smear showing ring-form parasites in >5% of RBCs with multiple parasites per RBC. Which malaria species is most likely?
- Plasmodium vivax
- Plasmodium falciparum (Correct answer)
- Plasmodium malariae
- Plasmodium ovale
Correct answer: Plasmodium falciparum
Plasmodium falciparum causes high-density parasitemia (>5% RBCs infected), multiple ring forms per cell, and is responsible for cerebral malaria and life-threatening complications.
Question 4: A patient presents with descending flaccid paralysis, dry mouth, diplopia, and ptosis after eating home-canned green beans. Autonomic function is preserved. Which toxin mechanism is responsible?
- Irreversible inhibition of acetylcholinesterase at the neuromuscular junction
- Blockade of presynaptic acetylcholine release at the neuromuscular junction (Correct answer)
- Competitive antagonism of nicotinic receptors
- Inhibition of glycine release in the spinal cord
Correct answer: Blockade of presynaptic acetylcholine release at the neuromuscular junction
Botulinum toxin cleaves SNARE proteins, blocking presynaptic acetylcholine vesicle release at the neuromuscular junction, causing flaccid paralysis.
Question 5: Which of the following is a reliable clinical feature distinguishing heat stroke from severe heat exhaustion?
- Core temperature > 40°C
- Diaphoresis
- Central nervous system dysfunction (Correct answer)
- Hypotension
Correct answer: Central nervous system dysfunction
CNS dysfunction (altered mentation, seizures, coma) is the defining feature of heat stroke and differentiates it from heat exhaustion, where cognition remains intact.
Question 6: A patient is bitten by a copperhead snake and develops local swelling to the forearm. Which of the following is the STRONGEST indication for antivenom (Crotalidae polyvalent immune Fab)?
- Bite site pain and erythema only
- Swelling progressing across one joint boundary (Correct answer)
- Nausea and vomiting without systemic bleeding
- Isolated thrombocytopenia without bleeding
Correct answer: Swelling progressing across one joint boundary
Rapidly progressive edema crossing joint boundaries indicates significant envenomation and warrants antivenom (CroFab) to prevent compartment syndrome and tissue necrosis.
Question 7: A patient presents with altered mental status, hyperthermia, lead-pipe rigidity, and markedly elevated CPK after starting haloperidol two weeks ago. What distinguishes neuroleptic malignant syndrome (NMS) from serotonin syndrome?
- NMS has slower onset and lead-pipe rigidity; SS has rapid onset and clonus/hyperreflexia (Correct answer)
- NMS is caused by serotonin excess; SS is caused by dopamine blockade
- NMS presents with diarrhea; SS presents with constipation
- NMS always has a higher temperature than SS
Correct answer: NMS has slower onset and lead-pipe rigidity; SS has rapid onset and clonus/hyperreflexia
NMS develops over days-weeks with lead-pipe rigidity and lacks the clonus/hyperreflexia of serotonin syndrome, which has rapid onset (hours) after serotonergic drug exposure.
ABEM Toxicology, Environmental & Infectious Diseases 4
A scuba diver surfaces too quickly and develops joint pain, dyspnea, and marbling of the skin.
Which chamber pressure is used in hyperbaric oxygen therapy for decompression sickness?