A 4-year-old boy is brought to the emergency department with dehydration. He has had several days of decreased oral intake, and today his parents could not get him to drink anything. The patient has received no vaccinations due to parental beliefs. Vital signs are normal except for mild tachycardia. Physical examination shows decreased skin turgor and sunken eyes. His jaw muscles are tight. Neurologic examination shows increased tone throughout and 3+ patellar reflexes. There is a small, healed puncture wound on his lower leg. The father says that the boy fell on a piece of chain-link fence in their backyard last week. Release of which of the following neurotransmitters is most likely to be directly impaired in this patient?

Question

A 4-year-old boy is brought to the emergency department with dehydration.  He has had several days of decreased oral intake, and today his parents could not get him to drink anything.  The patient has received no vaccinations due to parental beliefs.  Vital signs are normal except for mild tachycardia.  Physical examination shows decreased skin turgor and sunken eyes.  His jaw muscles are tight.  Neurologic examination shows increased tone throughout and 3+ patellar reflexes.  There is a small, healed puncture wound on his lower leg.  The father says that the boy fell on a piece of chain-link fence in their backyard last week.  Release of which of the following neurotransmitters is most likely to be directly impaired in this patient?

Quizplus · Accepted Answer

11ec160b_3b12_ed13_9249_9f2de567f978_MD0001_00 This unvaccinated child has evidence of tetanus (Clostridium tetani infection) following a puncture wound. C tetani causes disease not through tissue invasion but by producing a potent metalloprotease exotoxin (tetanospasmin) that is deadly in nanogram quantities. The toxin first binds to receptors on the presynaptic membranes of peripheral motor neurons. From there, it migrates by retrograde axonal transport to central inhibitory neurons in the spinal cord and brain stem and prevents release of the inhibitory neurotransmitters glycine and gamma-aminobutyric acid (GABA). Suppression of inhibitory nerve activity results in increased activation of motor nerves, causing muscle spasms and hyperreflexia. Classic features include difficulty opening the jaw (lockjaw, or trismus), a fixed sardonic smile (risus sardonicus), and contractions of back muscles resulting in backward arching (opisthotonos). Patients are also extremely irritable and develop tetanic spasms in response to minor stimuli such as loud noises. (Choice A) Acetylcholine release is inhibited by the botulinum toxin from C botulinum, leading to the flaccid paralysis seen in clinical botulism. (Choices B and C) Neither dopamine nor glutamate release has been linked to toxin effects in humans. (Choice E) Serotonin release from enterochromaffin cells in the gastrointestinal tract is stimulated by Vibrio cholera enterotoxin. This increased serotonin release contributes to the extreme fluid secretion seen in cholera. Educational objective: Tetanospasmin is a neuro-exotoxin released by Clostridium tetani. The toxin blocks the release of glycine and gamma-aminobutyric acid (GABA) from the spinal inhibitory interneurons that regulate the lower motor neurons. These disinhibited motor neurons cause increased activation of muscles, leading to spasms and hyperreflexia.

A 4-Year-Old Boy Is Brought to the Emergency Department with Dehydration