Question 275

Question:

A mother brings in her 9-month-old son complaining of a three day history of poor feeding. She reports that he has not fed well and has not had a bowel movement in this time. She feeds him home-processed vegetables from their garden. His immunizations are up-to-date. On exam, the infant has a decrease in muscle tone, abdominal distention, and labored breathing. What is/are the most likely etiologic agent(s)?

Correct Answer: C.  Neurotoxin preventing the release of acetylcholine from presynaptic nerve terminals

This boy likely has infant botulism (C). Ingested spores of the bacterium Clostridium botulinum can germinate in an infant’s gut and produce botulinum toxin that prevents acetylcholine release from presynaptic nerve terminals, thus affecting somatic and autonomic neuromuscular junctions alike. This results in flaccid paralysis, poor feeding, and constipation. Severe neurotoxin poisoning can result in respiratory failure. Infants are particularly sensitive to honey because their immune systems are not fully mature, and cannot prevent spore proliferation.

Autoimmune antibodies targeting the post-synaptic acetylcholine receptor (A) are seen in myasthenia gravis, an autoimmune disease characterized by muscle weakness that worsens as the day progresses.

Lead poisoning (B) can result in lethargy, poor feeding, and constipation. However, there is no given history suggestive of heavy metal ingestion. In addition, lead poisoning typically occur secondary to chronic exposure, so the presentation is either sub-acute or chronic (weeks to months rather than days).

A point mutation resulting in defective muscular protein (D), dystrophin, describes Duchenne muscular dystrophy, an X-linked genetic disease resulting in progressive proximal muscle weakness. The acute onset of this infant’s symptoms is not consistent with DMD.

A virus that results in necrosis of the spinal cord’s anterior horn (E) describes poliomyelitis. The virus is spread by the fecal-to-oral route, and severe cases lead to flaccid paralysis. While this infant has acute-onset decreased muscle tone, which could be consistent with poliomyelitis, this is much less likely because: (1) the virus does not typically affect autonomic nerves of the gut (as the findings of constipation suggest), and (2) his immunizations are up-to-date – poliomyelitis is extremely rare in the United States due to immunizations in the first year of life.