4

4 CASE 4


A 48-year-old man comes to the emergency department complaining of trouble seeing and has difficulty swallowing.


The patient is not from the area but is visiting friends who live on a commune. On questioning, the patient indicates that approximately 24 hours earlier he ate some green beans that were canned at the commune. Symptoms began 3 hours ago, and the decision to come to the emergency department was made because of his difficulty in swallowing. The patient is now anxious and easily excited.



PHYSICAL EXAMINATION



VS: T 37°C, P 90/min, R 19/min, BP 145/100 mm Hg

PE: Physical examination reveals double vision and drooping of the eyelids. The patient is slurring his speech and has difficulty swallowing. He shows signs of muscle weakness. Deep tendon reflexes are diminished in the legs and arms.


LABORATORY STUDIES



CBC, electrolytes: Normal

Brain CT and MRI: Normal (rule out cerebrovascular accident)

Cerebrospinal fluid examination: Normal

Electromyography: Nerve conduction velocity and amplitude normal; neuromuscular junction impaired

Edrophonium (Tensilon) test: Normal (rule out myasthenia gravis, myasthenic syndrome)

Stool sample: Positive for Clostridium botulinum


DIAGNOSIS


Botulism toxicity



COURSE


Botulism is a paralytic illness caused by a neurotoxin released from Clostridium botulinum. There are seven types of C. botulinum bacteria, identified by the letters A through G. The bacteria grow best in low oxygen conditions, and food-borne botulism is usually caused by eating contaminated foods canned at home.



PATHOPHYSIOLOGY OF KEY SYMPTOMS


Acetylcholine is stored in vesicles in the presynaptic terminal of alpha (α)-motor neurons. After an action potential arrives, calcium enters the presynaptic terminal, causing the vesicles to migrate toward the presynaptic membrane. There are numerous proteins involved in vesicle exocytosis. The SNAP-SNARE mechanism includes proteins that mediate vesicle docking and fusion, including synapsin 1, synaptobrevin, SNAP-25, syntaxin, synaptotagmin, and synaptophysin. The series of SNAP and SNARE proteins allow docking of the vesicles with the cell membrane, fusion, and, finally, exocytosis of the acetylcholine into the synaptic cleft (Fig. 4-1). The acetylcholine diffuses across the synaptic cleft and binds to receptors on the end plate region of the skeletal muscle cell.


image

FIGURE 4–1 Release of acetylcholine from synaptic vesicles at the neural membrane of the neuromuscular junction. Note the proximity of the release sites in the neural membrane to the acetylcholine receptors in the muscle membrane, at the mouths of the subneural clefts.

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Jul 4, 2016 | Posted by in PHYSIOLOGY | Comments Off on 4

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