BOTULISM

DEF: Neurotoxicity caused by Clostridium botulinum exotoxin, which irreversibly blocks acetylcholine release from presynaptic terminals of cholinergic neurons at the neuromuscular junction.
ETIOL: Infant botulism is distinct from food-borne and wound botulism in that it is caused by ingestion of C. botulinum spores rather than the exotoxin itself. Spores germinate in the intestine and generate exotoxin, which is distributed hematogenously. Infant botulism accounts for two-thirds of reported botulism cases in the United States. Although the toxin does not cross the blood–brain barrier, it accesses the cyto-plasmic membrane of peripheral cholinergic nerve endings, preventing exocytosis of acetylcholine at the neuromuscular junction. The resulting flaccid paralysis is potentially fatal. Infant botulism occurs almost exclusively within the first year of life and typically between 5 and 12 weeks of life. Honey has been implicated as the source of spores in 20% of cases; the contaminants have also been recovered from corn syrup. Yard soil is an environmental source of spores.
CLIN: History should focus on food intake and environmental exposures. Constipation often is the first sign of illness and typically is overlooked. Infants become listless and weak over the course of several days to weeks. Bulbar muscle involvement results in difficulty feeding and a weak cry. Drooling and pooling of food and secretions in the posterior pharynx may occur. Ptosis, ophthalmoplegia, diminished facial expression, and generalized muscle weakness and hypotonia (manifested initially as a loss of head control) are common findings. In severe cases, respiratory arrest can occur abruptly and may account for some cases of unexpected sudden death in infancy.
STUDIES: The diagnosis is confirmed by stool culture for C. botulinum, identification of toxin in the blood or stool, and electromyography.
TX: Treatment is directed toward aggressive supportive care, with particular attention to respiratory support. Infant botulism is a self-limited disease, typically lasting 2 to 6 weeks. Antitoxin and antibiotics do not influence the disease course; in fact, bacterial death caused by antibiotics can result in increased toxin release in the GI tract. In severe cases, infants may require prolonged ventilatory support. Constipation may persist for months and may improve with the use of stool softeners and adequate hydration. Close follow-up is required because relapse of infant botulism can occur after apparent resolution of clinical symptoms. The mortality rate of recognized cases of infant botulism is approximately 3%.