The Eyes Have It

Posted by • September 7th, 2012

A 69-year-old man presented to the emergency department 2 hours after awakening with slurred speech. He also reported difficulty chewing, blurry vision in both eyes, generalized weakness, and unsteady gait.

Clostridium botulinum is a neurotoxigenic, anaerobic, gram-positive, spore-forming bacillus named after an outbreak of sausage poisoning in the late 1700s (botulus is Latin for sausage). Of the variants of botulism, foodborne and wound botulism are the most common in adults. The manifestations of illness are due to botulism’s potent neurotoxin, with the majority of cases in the United States caused by botulinum toxins A, B, and E. Foodborne botulism classically occurs after ingestion of spores contained in improperly prepared home-canned foods, particularly vegetables, meat, and seafood.

Clinical Pearls

What are the characteristic gastrointestinal findings of foodborne botulism, and what is the timing in relation to neurologic symptoms?

The initial gastrointestinal symptoms of foodborne botulism typically occur within 12 to 72 hours after ingestion of the spores. Although not prominent in this case, these symptoms include constipation, vomiting, abdominal cramps, and, less commonly, diarrhea. Neurologic manifestations follow, initially with ophthalmologic and other bulbar signs.

What are the characteristic neurologic features of botulism?

Botulism should be considered when three or more of the “Dozen D’s” are present. These are, in the typical order of their appearance: dry mouth, diplopia (indicating involvement of cranial nerve III, IV, or VI), dilated pupils, which may be unresponsive to light, droopy eyelids (ptosis), droopy face, diminished gag reflex, dysphagia, dysarthria, dysphonia, difficulty lifting head, descending paralysis (usually symmetric and flaccid) and dyspnea from diaphragmatic paralysis.

Table 1. Signs and Symptoms of Foodborne Botulism Types A and B (“Dozen D’s”), in the Typical Order of Their Appearance.

Morning Report Questions

Q: How would one distinguish myasthenia gravis from botulism?

A: Botulism and myasthenia gravis both target the neuromuscular junction. Botulism results from a neurotoxin that prevents the presynaptic release of acetylcholine; myasthenia gravis is caused by antibodies directed against the postsynaptic acetylcholine receptor. Clinically, they are often difficult to distinguish, though myasthenia gravis is often manifested by fluctuating muscle weakness with fatigability. Status with respect to progressive pupillary changes differs between these disorders; most patients with botulism lose pupillary reactivity, whereas patients with myasthenia gravis do not. Key features of botulism are dilated, poorly reactive pupils; ptosis; a descending, flaccid, symmetric pattern of paralysis of the motor and autonomic nerves, with more proximal than distal muscle involvement and acute respiratory failure; preserved reflexes; normal findings in the cerebrospinal fluid; absence of fever and tremor; and normal cognition, sensation, and cerebellar studies. Tests for antibodies against the acetylcholine receptor as well as the edrophonium (Tensilon) test are useful in the diagnosis of myasthenia gravis.

Q: What is the treatment for botulism?

A: Ventilatory support and antitoxin are the cornerstones of treatment for botulism. Ventilatory support is required for 2 to 8 weeks for most patients, and up to 7 months for some, which is the time needed to sprout new presynaptic terminals and form new synapses. Intravenous equine trivalent antitoxin (for types A, B, and E) or bivalent antitoxin (for types A and B), which can be obtained from state health departments or the Centers for Disease Control and Prevention, is most effective if given within the first 24 hours after the onset of symptoms or within 72 hours after ingestion of contaminated food. Mortality from foodborne botulism in the United States has decreased from 25%, during the period from 1950 through 1959, to 6%, during the period from 1990 through 1996. This improvement is attributed to advances in supportive care and earlier administration of antitoxin.

One Response to “The Eyes Have It”

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