Pathophysiology
- A neuromuscular junction (NMJ) disorder → botulinum toxin irreversibly blocks the presynaptic release of acetylcholine → affecting bulbar and autonomic function.
Clinical features
- Rapid onset descending weakness causing bulbar palsy, ataxia, diplopia, and flaccid paralysis despite patient being fully conscious and without any sensory disturbance.
Investigation
- EMG
- Botulism EMG test results similar to lambert Eaton syndrome
- LES: Ab vs pre synaptic Ca Channels → reduce acetylcholine release
- LEMS
- ≥60% increment at high-fq (20-50 Hz) stimulation or postexercise facilitation
- MG
- Decrement at low-fq (2-5 Hz) stimulation (LRS)
- Higher rates of stimulation lead to increased calcium in the presynaptic terminal, which allows more acetylcholine to be released in presynaptic disorders such as botulism and LEMS, thereby increasing the response of muscle. However, in myasthenia gravis, which is characterized by loss of acetylcholine receptors postsynaptically, there is no increase in response at higher rates of stimulation, because there is already a maximal amount of acetylcholine present in the synaptic cleft.
Treatment
- Antitoxin is only effective if given early—once toxin has bound its actions cannot be reversed
- Supportive care including intubation and ventilation and treatment of autonomic disturbances may be required
Made with Bullet