A 6-month-old boy is brought to the emergency department due to poor feeding. His mother says, "My son normally nurses every 3 hours, but for the past 24 hours, he hasn't been latching or sucking when I offer him the breast. A few days ago, his eyelids started to appear droopy, and they don't open fully today. He also was previously able to roll and sit by himself, but today he is only lying down and not doing anything." The infant normally stools 2-3 times per day but has not stooled for 7 days, despite the family giving him small amounts of prune juice. He was born at 40 weeks gestation by vaginal delivery after an uncomplicated pregnancy. Immunizations are up to date, and he takes no medications. He lives on a large rural farm with his parents and grandfather. Temperature is 36.7 C (98 F), pulse is 128/min, respirations are 30/min, and pulse oximetry is 99% on room air. Physical examination demonstrates a hypotonic infant lying with arms and legs splayed outward on the examination table. He has bilateral ptosis and poor suck. Gag reflex is intact.
Which of the following is the most likely mechanism of this patient's condition?

Question

A 6-month-old boy is brought to the emergency department due to poor feeding.  His mother says, "My son normally nurses every 3 hours, but for the past 24 hours, he hasn't been latching or sucking when I offer him the breast.  A few days ago, his eyelids started to appear droopy, and they don't open fully today.  He also was previously able to roll and sit by himself, but today he is only lying down and not doing anything."  The infant normally stools 2-3 times per day but has not stooled for 7 days, despite the family giving him small amounts of prune juice.  He was born at 40 weeks gestation by vaginal delivery after an uncomplicated pregnancy.  Immunizations are up to date, and he takes no medications.  He lives on a large rural farm with his parents and grandfather.  Temperature is 36.7 C (98 F), pulse is 128/min, respirations are 30/min, and pulse oximetry is 99% on room air.  Physical examination demonstrates a hypotonic infant lying with arms and legs splayed outward on the examination table.  He has bilateral ptosis and poor suck.  Gag reflex is intact. 
Which of the following is the most likely mechanism of this patient's condition?

Quizplus · Accepted Answer

Explanation: 11ec2b69_c198_a6d8_8f63_c9dfbd7e7d41_MD0005_00 Infant botulism is a flaccid neuropathy that occurs in children age <1 following the ingestion of Clostridium botulinumspores. These spores are typically found in honey as well as environmental dust/soil, particularly in rural or farm areas where the soil is frequently disturbed. Although ingestion of the spores is unlikely to harm a healthy adult, infants have an immature digestive system that lacks protective enteric microbiota. Therefore, the spores are able to colonize the gastrointestinal tract and produce toxin in situ. This neurotoxin inhibits presynaptic acetylcholine release into the neuromuscular junction, causing dysfunction of the skeletal and smooth muscles. Nonspecific early manifestations include constipation and poor feeding, as seen in this infant. Over time patients develop oculobulbar weakness, which may result in ptosis, impaired pupillary constriction, poor suck, and/or absent gag reflex. Muscle weakness can progress to descending paralysis and respiratory failure. Neurologic examination reveals symmetric hypotonia, diminished or absent deep tendon reflexes, and decreased strength. (Choice A) Acetylcholine receptor antibodies in the neuromuscular junction are implicated in myasthenia gravis. Ptosis is a common presenting symptom; however, constipation is not associated, and a slow progression of fluctuating muscle weakness and fatigue is characteristic. (Choice B) Degeneration of anterior horn cells describes spinal muscular atrophy, which causes flaccid paralysis, hyporeflexia, and fasciculations. It is unlikely in this infant who was developing appropriately until a week prior to presentation. (Choice C) Demyelination of peripheral nerve axons occurs with Guillain-Barré syndrome, which is rare in infants and characterized by ascending paralysis. Ptosis is an uncommon concurrent finding. (Choice E) A traumatic injury to the spinal cord could result from nonaccidental trauma, which should be considered in an infant with altered mental status. However, this patient has no red flags for child abuse, and upper motor neuron findings (eg, hypertonia) are expected with spinal cord lesions. Educational objective: Infant botulism is caused by ingestion of Clostridium botulinum spores, which produce a neurotoxin that inhibits presynaptic acetylcholine release at neuromuscular junctions. Classic findings include constipation, oculobulbar weakness, and descending flaccid paralysis in a previously healthy infant. References: Acute muscular weakness in children. (http://www.ncbi.nlm.nih.gov/pubmed/28489146) Clinical mimics of infant botulism. (http://www.ncbi.nlm.nih.gov/pubmed/17403857)

A 6-Month-Old Boy Is Brought to the Emergency Department Due