Which of the following is not a feature of botulism: diarrhea, extensor plantar (extensor plantar response), post-tetanic potentiation, or circumoral paresthesias?

Features of Botulism: Identifying Non-Characteristic Symptoms

Diarrhea is NOT a characteristic feature of botulism, with constipation being much more common in botulism cases. 1

Clinical Features of Botulism

Botulism is characterized by a classic triad:

1. Symmetric descending flaccid paralysis with prominent bulbar palsies (93% of cases)
2. Afebrile presentation (99% of cases)
3. Clear sensorium (mental status typically preserved) 1, 2

Common Neurological Manifestations

• Descending paralysis (93%)
• Dysphagia (85%)
• Weakness or fatigue (85%)
• Ptosis (81%)
• Blurred vision (80%)
• Difficulty speaking/dysarthria (78%)
• Diplopia (75%)
• Change in voice (69%)
• Shortness of breath (65%) 1

Gastrointestinal Symptoms

• Constipation is a common early symptom (30% of cases)
• Nausea (43%) and vomiting (33%) are more common than diarrhea
• Diarrhea is rare, occurring in only 16% of cases 1

Analysis of Listed Features

1. Diarrhea: NOT a typical feature of botulism. Constipation is much more characteristic of botulism than diarrhea 1. This is the correct answer to the question.

2. Extensor plantar response: Not mentioned as a characteristic feature in the guidelines. Botulism causes flaccid paralysis with decreased reflexes rather than upper motor neuron signs like extensor plantar responses 1, 3.

3. Post-tetanic potentiation: This is a characteristic electrophysiological finding in botulism. Electrophysiologic testing typically shows small evoked muscle action potentials, and post-tetanic facilitation can be found in affected muscles 3.

4. Circumoral paresthesias: While sensory deficits and paresthesias are not the most typical manifestations of botulism (occurring in only 17% of cases), circumoral paresthesias can be a possible symptom 1.

Pathophysiology Explanation

Botulinum toxin causes temporary muscle paralysis by inhibiting acetylcholine release at the neuromuscular junction, specifically cleaving the synaptic Vesicle Associated Membrane Protein (VAMP) 1. This mechanism explains the predominantly motor symptoms with relative sparing of sensory function.

Clinical Pitfalls to Avoid

• Don't mistake botulism for other neurological conditions with similar presentations such as Guillain-Barré syndrome, myasthenia gravis, stroke, or Lambert-Eaton syndrome 4, 5
• Remember that botulism is afebrile - presence of fever should prompt consideration of alternative diagnoses
• Early gastrointestinal symptoms like nausea and vomiting in foodborne botulism are caused by other clostridial products or non-clostridial substances related to food spoilage, rather than the botulinum neurotoxin itself 1