Ophthalmologic Manifestations of Botulism Workup

Updated: May 19, 2016
  • Author: Bhupendra C K Patel, MD, FRCS; Chief Editor: Hampton Roy, Sr, MD  more...
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Approach Considerations

Diagnosis of botulism requires a thorough clinical history, assessment of the timing and progression of neurologic symptoms, assessment of recent diet, assessment of bowel habits, and a high index of suspicion. [13]

Most initial laboratory findings are normal, except for mild dehydration, especially in infants.

A diagnosis of botulism is confirmed via detection of the organism or botulinum toxin in stool, serum, would exudates, tissue specimens, or the implicated food source. As C botulinum is not part of normal flora in infants or adults, culture that is positive for C botulinum in a symptomatic patient should be considered diagnostic of botulism. Botulinum toxin is detected in serum or stool specimens in approximately 46% of clinically diagnosed cases. In foodborne cases, serum toxin assay results may remain positive for up to 16 days after admission, and stool cultures grow C botulinum in approximately 70% of cases.

In infant botulism, toxin is detected in a serum specimen only early in the course of the illness and before antitoxin administration. Serum toxin assay results are positive in only 1% of reported cases of infant botulism in the United States.

Stool, enema, and gastric aspirates are cultured and examined for toxin assay. Suspect foods should be collected.

A mouse neutralization assay is used to detect toxin from specimens; this is the most sensitive and specific method of assay available.

Enriched media are needed to culture and isolate C botulinum.

Severity and duration of the illness have been reported to be worse in cases due to type A than type B toxin.


Laboratory Studies

The diagnosis of botulism requires a high degree of clinical suspicion. The diagnosis must be considered in an afebrile patient with progressive descending paralysis, especially in the presence of gastrointestinal symptoms.

Serum toxin bioassay: The demonstration of toxin in serum involves a bioassay in mice. The identification of the toxin type is performed by a mouse toxin neutralization test.

Isolation of organism by culture

Food-borne: The demonstration of organism (or its toxin) in vomitus, gastric aspirate, or feces is highly suggestive of the diagnosis of botulism, because intestinal carriage is rare. Anaerobic cultures are required. Early cases of botulism are more likely to involve diagnosis by toxin assay, whereas later cases are more likely to yield a positive specimen culture.

Wound culture: In wound botulism, wound cultures yielding the organism are highly suggestive of botulism.

Source culture: Isolation of the organism from food without toxin is not sufficient for a diagnosis.


Other Tests

Electrophysiology: Nerve conduction velocity is normal.

Electromyography shows a distinctive pattern of brief, small-amplitude, overly abundant motor unit potentials.