What are the symptoms of botulism?

Symptoms of Botulism

Botulism presents as a characteristic triad of symmetric descending flaccid paralysis with prominent bulbar palsies, absence of fever, and a clear sensorium. 1, 2

Classic Neurologic Presentation

The hallmark pattern is descending paralysis (93% of cases), typically beginning with cranial nerve involvement before progressing downward. 1

Initial Cranial Nerve Symptoms (Most Common)

• Ptosis (drooping eyelids) occurs in 81% of patients 1
• Blurred vision affects 80% of patients 1
• Diplopia (double vision) presents in 75% of cases 1
• Dysphagia (difficulty swallowing) occurs in 85% of patients 1
• Difficulty speaking (dysarthria, slurred speech) affects 78% of patients 1
• Voice changes (hoarseness, nasal speech) occur in 69% of cases 1

These ocular symptoms are considered the most objective early findings and should prompt immediate consideration of botulism. 1

Bulbar and Oropharyngeal Signs

• Dry mouth is present in 63% of patients 1
• Thick tongue sensation occurs in 62% of cases 1
• Extraocular palsy affects 60% of patients 1
• Impaired gag reflex is found in 58% of cases 1
• Palatal weakness occurs in 54% of patients 1
• Facial weakness (including droop and paralysis) affects 47% of cases 1

Systemic and Progressive Symptoms

Generalized Weakness and Respiratory Involvement

• Generalized weakness or fatigue occurs in 85% of patients 1
• Shortness of breath (respiratory distress, dyspnea) develops in 65% of cases 1
• Dizziness affects 55% of patients 1

Respiratory compromise can occur early when upper airway muscles are affected, causing pharyngeal collapse or secretion pooling, even before diaphragmatic involvement. 1

Pupillary Findings

• Dilated pupils are present in 37% of cases 1
• Abnormally reactive pupils (sluggish, poorly reactive, or fixed) occur in 24% of patients 1
• Constricted pupils are rare (only 3% of cases) 1

Gastrointestinal Symptoms

• Nausea occurs in 43% of patients 1
• Vomiting affects 33% of cases 1
• Constipation is present in 30% of patients 1
• Abdominal pain occurs in 25% of cases 1
• Diarrhea affects 16% of patients 1

Critical Distinguishing Features

What Botulism Is NOT

• Patients remain afebrile (temperature <100.4°F/<38°C) in 99% of cases 1, 2
• Mental status remains clear in 92% of cases (altered mental status occurs in only 8%) 1
• Sensory deficits or paresthesias are uncommon (only 17% of cases) 1
• Urinary retention is rare (9% of cases) 1

The presence of fever should prompt consideration of alternative diagnoses or concurrent infection. 1

Important Clinical Caveats

Atypical Presentations

Some patients present with less specific initial complaints that can delay diagnosis, including gastrointestinal symptoms alone, back pain, altered consciousness, or lip and tongue numbness. 1 These atypical presentations are associated with delayed diagnosis and worse outcomes. 1

Rare but Reported Findings

Although uncommon, fever, nondescending paralysis, and altered mental status have been documented in confirmed cases. 1 Botulism typically affects proximal muscles before distal muscles, but equal or even reversed patterns have been reported. 1

Mimics to Consider

The symptom constellation can resemble anxiety disorders (dry mouth, difficulty swallowing, nausea, dizziness), making it essential to focus on objective ocular findings for diagnosis. 1 Botulism is commonly confused with myasthenia gravis, Guillain-Barré syndrome, and cerebrovascular stroke. 1, 2

Respiratory Failure

While respiratory failure without preceding neurologic deficits has rarely been reported as the presenting symptom, this is highly improbable and likely represents inadequate neurologic examination rather than true isolated respiratory presentation. 1