A 4-month-old boy is brought to the emergency department due to poor feeding and a weak cr… — USMLE Step 2 CK

A 4-month-old boy is brought to the emergency department due to poor feeding and a weak cry for the past 3 days. The parents report that he has been progressively less active and has not had a bowel movement in 5 days. He was previously healthy and exclusively breastfed, though the parents recently began dipping his pacifier in honey to soothe him. He was born at full term and his newborn screen was normal. His temperature is $37.1^\circ C$ ( $98.8^\circ F$ ), heart rate is $140/\text{min}$ , and respiratory rate is $35/\text{min}$ . On physical examination, the infant appears listless. He has bilateral ptosis, sluggish pupillary responses to light, and an absent gag reflex. There is marked head lag and generalized hypotonia. The abdomen is soft and non-distended with hypoactive bowel sounds. Laboratory testing shows a thyroid-stimulating hormone (TSH) level of $2.4 \mu\text{U/mL}$ (normal: $0.5-5.0 \mu\text{U/mL}$ ). Which of the following is the most appropriate next step in management for this patient?

Intravenous administration of human-derived botulism immune globulinAnswer
B
Nasogastric tube decompression and surgical consultation
C
Referral to early intervention for developmental delay
D
Intravenous administration of broad-spectrum antibiotics
E
Initiation of levothyroxine therapy

Answer

Intravenous administration of human-derived botulism immune globulin

The correct answer is intravenous administration of human-derived botulism immune globulin. This infant presents with the classic clinical triad of infant botulism: bulbar palsies (ptosis, sluggish pupillary responses, absent gag reflex, weak cry), descending flaccid paralysis (marked head lag, generalized hypotonia), and autonomic dysfunction (severe constipation, hypoactive bowel sounds). The recent exposure to honey, which can contain *Clostridium botulinum* spores, strongly supports this diagnosis. Infant botulism occurs when ingested spores colonize the gastrointestinal tract and produce botulinum toxin in vivo. The toxin irreversibly inhibits presynaptic acetylcholine release at the neuromuscular junction. Management requires immediate intravenous administration of human-derived botulism immune globulin (BIG-IV). This antitoxin neutralizes circulating free toxin, preventing further progression of paralysis, and should be administered as soon as the clinical diagnosis is suspected, without waiting for confirmatory stool toxin assays.

Step-by-Step Solution

Identify the clinical syndrome based on the patient's history and physical examination.

The infant presents with acute bulbar palsies (ptosis, absent gag reflex, weak cry), descending flaccid paralysis (head lag, hypotonia), and autonomic dysfunction (constipation) after honey exposure.

Recognizing this classic triad is essential for diagnosing infant botulism, an acute neurologic emergency caused by Clostridium botulinum spores.

Determine the underlying pathophysiology of the disease.

In vivo production of botulinum toxin irreversibly inhibits the presynaptic release of acetylcholine at the neuromuscular junction.

Understanding the mechanism explains the combination of autonomic (constipation, sluggish pupils) and motor (flaccid paralysis) findings.

Select the most appropriate initial management step.

Immediate intravenous administration of human-derived botulism immune globulin (BIG-IV) is required.

BIG-IV neutralizes circulating free toxin and halts the progression of paralysis. It must be administered as soon as the condition is suspected clinically, prior to confirmatory stool testing.

Key Concept

Infants presenting with acute descending flaccid paralysis, bulbar palsies, and constipation (often following honey exposure) should be clinically diagnosed with infant botulism and treated immediately with intravenous human-derived botulism immune globulin.

Question

Answer

Step-by-Step Solution

Key Concept

Common Mistakes

Topics

More questions from this topic