A 27-year-old woman presents to the urgent care clinic for evaluation of muscle weakness, excessive salivation, and diarrhea which started one hour ago. She was picking apples when her symptoms began, and she has never before experienced these symptoms. Past medical history is significant for endometriosis, for which she takes a combined oral contraceptive pill. Vital signs are significant for a heart rate of 45 beats per minute, and physical examination reveals diffuse weakness, wheezing, excessive salivation, and excessive lacrimation.
Which of the following best describes the most likely mechanism of this patient’s symptoms?
C) Demyelination in the central nervous system
This patient is most likely experiencing organophosphate poisoning secondary to pesticide exposure from picking fruit. Organophosphates inhibit the enzyme acetylcholinesterase, resulting in excess acetylcholine activity and parasympathetic activation. This results in symptoms such as diarrhea, urination, miosis/muscle weakness, bronchospasm, emesis, lacrimation, and salivation/sweating (commonly remembered with the mnemonic DUMBELS). Treatment is with pralidoxime and atropine.
Answer choice A: Decreased receptor density at the neuromuscular junction, is incorrect. This describes myasthenia gravis, in which antibodies against the acetylcholine receptor at the neuromuscular junction lead to difficulty with muscle contraction. It often presents with ptosis as an initial symptom.
Answer choice B: Degeneration of anterior horn cells, is incorrect. This is the mechanism of amyotrophic lateral sclerosis (ALS), a progressive neurodegenerative disease that presents with upper and lower motor neuron signs.
Answer choice C: Demyelination in the central nervous system, is incorrect. This describes multiple sclerosis, an autoimmune condition that may present with episodes of vision impairment (often internuclear ophthalmoplegia), difficulty walking, and/or sharp tingling sensations (Lhermitte sign).
Answer choice D: Demyelination of peripheral nerves, is incorrect. This describes the mechanism of Guillain-Barré syndrome, which presents with gradual ascending weakness/paralysis. It usually occurs after infection (often Campylobacter) or vaccination.
Key Learning Point
Organophosphates inhibit acetylcholinesterase and increase acetylcholine activity at the neuromuscular junction, resulting in excess parasympathetic activation.
