What are the diagnostic steps for botulism in patients of all ages, particularly those with symptoms such as blurred vision, diplopia, ptosis, dysphagia, and dysarthria, and a history of consuming potentially contaminated food or exposure to environmental sources of the toxin?

How to Diagnose Botulism

Botulism diagnosis is primarily clinical and must be made rapidly based on a specific triad of findings—treatment decisions cannot wait for laboratory confirmation. 1

Clinical Diagnostic Criteria

Suspect botulism when ALL three of the following criteria are met: 1

1. Patient is Afebrile

• Temperature <100.4°F (<38°C) in 99% of confirmed cases 1
• Fever is exceedingly rare in adults and should prompt consideration of alternative diagnoses or concurrent infection 1, 2

2. Acute Onset of At Least ONE of These Symptoms:

• Blurred vision (occurs in 80% of cases) 1, 2
• Double vision/diplopia (occurs in 75% of cases) 1, 2
• Difficulty speaking including slurred speech or dysarthria (occurs in 78% of cases) 1, 2
• Voice changes including hoarseness or nasal speech (occurs in 69% of cases) 1, 2
• Dysphagia, pooling of secretions, or drooling (occurs in 85% of cases) 1, 2
• Thick tongue (occurs in 62% of cases) 1

3. At Least ONE of These Objective Signs:

• Ptosis (drooping eyelids—occurs in 81% of cases) 1, 2
• Extraocular palsy or fatigability (occurs in 60% of cases) 1
• Facial paresis with loss of facial expression or pooling of secretions (occurs in 47% of cases) 1
• Fixed or abnormally reactive pupils (occurs in 24% of cases) 1
• Descending paralysis beginning with cranial nerves (occurs in 93% of cases) 1, 2

Essential Clinical Features

The hallmark pattern is symmetric descending flaccid paralysis with prominent bulbar palsies and clear sensorium. 1, 2, 3

• Mental status remains intact in 92% of cases—altered mental status occurs in only 8% and suggests alternative diagnoses or complications like respiratory failure 1, 2
• Paralysis descends from cranial nerves downward to respiratory muscles, then trunk and extremities 1, 2, 4
• No sensory deficits are expected (sensory complaints occur in only 17% and are atypical) 1

Exposure History Assessment

Ask about specific exposures, but absence of typical risk factors does NOT exclude botulism: 1

• Foodborne botulism: Home-canned foods, fermented foods, improperly preserved foods 1
• Wound botulism: Injection drug use, especially black tar heroin 1, 5
• Infant botulism: Honey exposure in infants <12 months 4, 6
• Inhalational botulism: Potential bioterrorism exposure 1, 7

Critical caveat: Atypical and novel exposures can cause botulism, so lack of classic exposure history should not rule out the diagnosis 1

Ancillary Testing to Support Diagnosis

Treatment must begin based on clinical findings alone—do not wait for confirmatory testing. 1, 7

Electrodiagnostic Studies (EMG/NCS)

• Small evoked muscle action potentials in response to single supramaximal nerve stimulus in affected muscles 1, 4
• Posttetanic facilitation may be present in some affected muscles 4
• Incremental response to repetitive nerve stimulation at high frequencies 1
• These findings provide presumptive evidence when bioassay is negative 4

Laboratory Confirmation (Performed at CDC or State Labs)

• Detection of botulinum toxin in serum, stool, or wound specimens 4, 5
• Culture of C. botulinum from stool or wound 4
• Important limitation: Confirmatory testing may be insensitive in up to 32% of foodborne cases and takes days to complete 7

Tests to Rule Out Mimics

• Tensilon (edrophonium) test to exclude myasthenia gravis 1
• Lumbar puncture to exclude Guillain-Barré syndrome (normal CSF protein in botulism) 1
• Neuroimaging to exclude stroke 1, 3

Common Diagnostic Pitfalls

Botulism is frequently misdiagnosed as myasthenia gravis, Guillain-Barré syndrome, or stroke. 1, 2, 3

• Failure to perform thorough neurologic examination decreases likelihood of considering botulism 1
• Atypical presentations including isolated GI symptoms, back pain, or asymmetric findings can delay diagnosis and worsen outcomes 1, 2
• Respiratory failure as presenting symptom without preceding neurologic deficits is highly improbable and likely represents inadequate initial examination 1

Multiple Cases or Outbreak Setting

Occurrence of more than one case with epidemiologic connection substantially increases diagnostic likelihood and suggests common-source outbreak. 1

• Immediately notify public health authorities for all suspected cases 1
• Geographically dispersed cases without obvious connection do not rule out outbreak from widely distributed product 1