Laboratory Studies
Although clinical suspicion should be sufficient to prompt supportive therapy for botulism, other differential diagnoses must be excluded.
Obtain stool cultures in all patients, adding wound cultures if wound botulism is suspected.
Approximately 60% of food-borne cases yield positive stool culture results. Cultures may be enriched to enhance the growth of C. botulinum. [15] A positive culture finding in the presence of flaccid paralysis is diagnostic. Currently, specific assays for the toxin, including enzyme-linked immunoassays and polymerase chain reaction, are under investigation.
Currently, the mouse inoculation test is the best test available and can be performed by the Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia. In the assay, mice are injected with a serum sample or stool sample [8, 12] from the patient and test results are considered positive for toxin if the mice die of respiratory arrest within 24 hours. The exact type of toxin is determined through pretreating each mouse in a set of mice with a different type-specific antitoxin, then injecting the serum. The mouse left alive the next day is the one pretreated with the antitoxin to the toxin affecting the patient. The sensitivity of this test in the diagnosis of wound botulism has been questioned; strong clinical suspicion should outweigh a negative mouse inoculation test. [31, 32]
Serum testing for toxins is a less sensitive test than is testing feces for toxins, especially for infant botulism, and serum should be used only if stool samples cannot be obtained. [8, 12] When collecting samples of stool for botulinum toxin and spores, one must be very careful and use protective equipment, because of the great toxicity of the toxin. A sample of 25-50 grams of stool should be collected, although, sometimes smaller amounts in infants have yielded positive results. [12] Infants with botulism often have severe constipation and an enema may be necessary to obtain stool samples for spores and toxins. [8] Stool samples should be refrigerated in a leak proof container and shipped out to the testing laboratory as soon as possible. If possible stool samples should be collected prior to starting treatment with immune globulin, however this treatment should not be delayed waiting for the results of confirmatory testing. [12]
For infant botulism detecting botulism toxins or spores in stool is the best way to confirm the diagnosis. Detecting toxin in stool is much less sensitive. For food borne botulism detection of toxin in feces, serum, gastric aspirate or contaminated food is the best way to confirm the diagnosis. Also, cultures should be sent. For wound botulism detecting toxin in serum and culturing tissue from the wound are the best ways to confirm the diagnosis. For the rare cases of adult enteric botulism, detection of toxin in the feces and culture of the feces are the best ways to confirm the diagnosis. For the very rare case of iatrogenic botulism caused by the injection of too much toxin, detecting the toxin in the serum is the only way to confirm the diagnosis. Finally in the extremely rare case of inhalation botulism, the detection of toxin from a nasal swab is the way to confirm the diagnosis. [8]
It must be emphasized again that treatment with immune globulin should not be delayed waiting for confirmatory tests, but should be given based on a strong clinical suspicion. Delays in initiating treatment increase mortality and morbidity.
A Multiplex polymerase chain reaction test (PCR) has been described. [33, 34]
PCR testing for spores in stool has been done successfully. Results may be available before the results of mouse bioassays are. However, this testing is not widely available yet, and the sensitivities are yet to be determined. Local and state public health departments should be contacted for advice and assistance in getting specimens tested. [8]
Imaging Studies
Perform CT scanning or MRI as clinically indicated to exclude stroke.
Other Tests
See the list below:
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Perform an edrophonium chloride test to exclude myasthenia gravis, if indicated, although transient responses have been reported with botulism.
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Electromyelography (EMG) demonstrates a non-specific, decreased amplitude of action potentials. Rapid repetitive EMG at frequencies of 20-50 Hz is more specific for botulism and useful in excluding Guillain-Barré syndrome, but this response does not distinguish botulism from Lambert-Eaton syndrome. Infant botulism is characterized by a pattern known as brief, small, abundant motor-unit action potential on EMG in clinically affected muscles.
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The classical electromyography finding is neuro-muscular junction blockade with normal axonal conduction. However, the lack of this finding should not preclude the clinician from initiating treatment with immune globulin, if there is strong clinical suspicion of botulism. [15]
Procedures
See the list below:
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Lumbar puncture findings can usually exclude Guillain-Barré syndrome, a condition that tends to elicit a higher protein level in cerebrospinal fluid (especially later in the course of the disease) than does botulism. Also, lumbar puncture can help exclude the diagnosis of meningitis or encephalitis, as Botulism does not cause an increase in WBCs in the CSF.
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In wound botulism, wounds should be debrided and any foreign bodies removed as deemed necessary by the physician. [15]
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This is a photomicrograph of Clostridium botulinum stained with Gentian violet. The bacterium, C botulinum, produces a neurotoxin which causes the rare, but serious, paralytic illness, botulism.
