Botulism Workup

Updated: Feb 15, 2019
  • Author: Kirk M Chan-Tack, MD; Chief Editor: Pranatharthi Haran Chandrasekar, MBBS, MD  more...
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Laboratory Studies

Laboratory tests are not helpful in the routine diagnosis of botulism.

WBC counts and erythrocyte sedimentation rates are normal.

Cerebrospinal fluid is normal, except for occasional mild elevations in protein concentration.

A mouse neutralization bioassay confirms botulism by isolating the botulism toxin.

Toxin may be identified in serum, stool, vomitus, gastric aspirate, and suspected foods. C botulinum may be grown on selective media from samples of stool or foods. Note that the specimens for toxin analysis should be refrigerated, but culture samples of C botulinum should not be refrigerated.

Because intestinal carriage is rare, identifying the organism or its toxin in vomitus, gastric fluid, or stool strongly suggests the diagnosis. Isolation of the organism from food without toxin is insufficient grounds for the diagnosis. Only experienced personnel who have been immunized with botulinum toxoid should handle the specimens. Because the toxin may enter the blood stream through the eye or via small breaks in the skin, precaution is warranted.

Wound cultures that grow C botulinum suggest of wound botulism.


Imaging Studies

Imaging studies are generally not useful in the diagnosis of botulism.

The only potential role for imaging studies (eg, CT scan, MRI) would be to rule out CNS pathology, such as intracranial mass lesions, cerebrovascular disease of the brainstem, or basilar artery stroke, in patients in whom the presentation is atypical or vague.


Other Tests

Patients with botulism may have mild nonspecific abnormalities on electrocardiography.

Results from nerve conduction studies are normal, and electromyography (EMG) reveals reduced amplitude of compound muscle action potentials.

EMG may be useful in establishing a diagnosis of botulism, but the findings can be nonspecific and nondiagnostic, even in severe cases. Characteristic findings in patients with botulism include brief low-voltage compound motor-units, small M-wave amplitudes, and overly abundant action potentials. An incremental increase in M-wave amplitude with rapid repetitive nerve stimulation may help to localize the disorder to the neuromuscular junction. Single-fiber EMG may be a more useful and sensitive method for the rapid diagnosis of botulism intoxication, particularly in the absence of signs of general muscular weakness.

The results of the edrophonium chloride, or Tensilon, test for myasthenia gravis may be falsely positive in patients with botulism. If positive, it is typically much less dramatically positive than in patients with myasthenia gravis.