A 6-month-old boy is brought to the emergency department for poor feeding and decreased activity. For the past 5 days, the patient has been eating less. His normal intake is 26 oz of formula daily; recently, he has consumed only 10 oz of formula daily. The patient has had a few wet diapers daily but has not stooled for 5 days. In addition, he was previously able to sit with support and reach for toys but has been unable to do this in the past week. His parents are healthy. Immunizations are up to date. Weight and length are at the 65th percentile; head circumference is at the 75th percentile. Temperature is 36.7 C (98.1 F), pulse is 108/min, and respirations are 36/min. On examination, the patient has diminished head control with neck and shoulder-girdle weakness, generalized hypotonia, and reduced spontaneous movement. Eye movements are decreased with evidence of ptosis. The oral mucosa is dry. Complete blood count, serum electrolytes, renal and liver function tests, and erythrocyte sedimentation rate are normal. What is the best next step in management of this patient?
Infant botulism | |
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BP = blood pressure; CMAP = compound muscle action potential; EMG = electromyography; HR = heart rate. | |
This child age <12 months has acute-onset poor feeding with hypotonia, weakness, and cranial nerve dysfunction (eg, ptosis, decreased eye movements). In the setting of a normal laboratory evaluation, no fever, and decreased bowel movements, these findings are highly suspicious for infant botulism.
Pathogenesis of infant botulism involves ingestion of C botulinum spores that germinate in the immature digestive tract and produce toxin in situ. Ingestion of honey is implicated in approximately 15% of cases; a definitive exposure history is often absent, as in this patient. The neurotoxin inhibits presynaptic acetylcholine release into the neuromuscular junction, affecting the following:
Autonomic nervous system: Involvement of autonomic smooth muscle causes hypoactive bowel and constipation (eg, decreased bowel movement frequency), which is often the first symptom. Decreased salivation (eg, dry oral mucosa) can occur.
Somatic nervous system: Muscles innervated by cranial nerves are affected first, causing oculobulbar weakness (eg, absent gag reflex, ptosis, ophthalmoplegia). Muscular weakness (eg, poor suck/feeding) may progress to descending paralysis with symmetric weakness and hypotonia.
Because weakness can rapidly progress to respiratory failure (diaphragmatic paralysis), infant botulism is usually diagnosed clinically and treated promptly with antitoxin therapy (botulism immunoglobulin) while awaiting supportive (electromyography) and/or confirmatory testing (C botulinum spore/toxin assay from stool). Botulism antitoxin binds circulating neurotoxin, preventing symptom progression, but cannot reverse paralysis, which can take months to improve.
(Choices B and E) Empiric antibiotics are warranted for suspected sepsis or meningitis (for which lumbar puncture is also obtained). Both conditions can cause poor feeding and hypotonia, but other findings include fever, hemodynamic instability, and leukopenia or leukocytosis, not seen in this patient.
(Choice C) In neonates with mothers with myasthenia gravis, oculobulbar weakness and hypotonia can occur due to transplacental transfer of acetylcholine receptor antibodies. Unlike in this patient, symptoms present within hours to days of birth.
(Choice D) Suspected abusive head injury (nonaccidental trauma) warrants neuroimaging and should be considered in an infant with acute-onset poor feeding and reduced spontaneous movement. However, history is often inadequate or inconsistent with clinical findings, contrasting with this family's detailed feeding, elimination, and developmental history consistent with infant botulism. Moreover, CT scan, not MRI, would be the preferred initial imaging study in suspected traumatic brain injury.
Educational objective:
Botulism should be suspected in infants with constipation, oculobulbar weakness (eg, ptosis), and progressive weakness and hypotonia. Diagnosis is clinical, and botulism antitoxin should be administered promptly while awaiting confirmatory testing.