What is the relationship of UMNs and LMNs with the muscles?
-one UMN can innervate multiple muscles
-each LMN only innervates one muscle
What are the characteristics of myasthenia gravis?
-disease of neuromuscular junction
-lack of acetylcholine receptors
-can be congenital or acquired
What is acquired myasthenia gravis?
autoimmune disease directed against the nicotinic acetylcholine receptor on the motor end plate
What are potential triggers for acquired myasthenia gravis?
-hypothyroidism
-thymoma/other neoplasia
-methimazole therapy in cats
What are the signs of generalized acquired myasthenia gravis?
-exercise-associated weakness
-megaesophagus
-facial muscle weakness
What are the signs of focal acquired myasthenia gravis?
-weakness of isolated skeletal muscle groups
-pharyngeal, laryngeal, esophageal, and/or facial muscles are targets
-regurgitation
-megaesophagus
What are the signs of fulminant acquired myasthenia gravis?
-rapidly progressive tetraparesis
-regurgitation
-respiratory muscle involvement
What leads to the signs of myasthenia gravis?
quick depletion of available acetylcholine receptors
What are the hallmark signs of myasthenia gravis?
-exercise-induced stiffness
-tremors
-weakness that resolves with rest
What are the characteristics of congenital myasthenia gravis?
-born with insufficient acetylcholine receptors
-inherited; NOT auto-immune
-clinical signs begin around 1 to 2 months old
How is myasthenia gravis diagnosed?
-clinical features
-thoracic radiographs; looking for aspiration pneumonia
-acetylcholine receptor antibody titer (acquired form)
-edrophonium test
What are the characteristics of the edrophonium test?
-quick onset, short-acting acetylcholinesterase inhibitor
-inhibition of acetylcholinesterase prevents breakdown of acetylcholine; provides more time for acetylcholine to find reduced receptors
-response to drug can indicate myasthenia gravis
What is the treatment for myasthenia gravis?
-oral pyridostigmine or injectable neostigmine (megaesophagus patients)
-treatment of aspiration pneumonia
-feeding in upright Bailey chair
What is the potential side effect of acetylcholinesterase inhibition?
increased PNS activity with inhibition:
-salivation
-tearing
-urination
-diarrhea/defecation
-respiratory issues
What are the characteristics of immunosuppressive therapy for myasthenia gravis?
-indicated for patients refractory to anticholinesterases alone
-only indicated in acquired myasthenia gravis cases
-start with prednisone at a less-than-immunosuppressive dose
-can use secondary drugs like azathioprine, cyclosporine, cyclophosphamide, or mycophenolate
What are the characteristics of acquired myasthenia gravis monitoring?
-want to recheck antibody titer every 6 to 8 weeks
->80% of dogs go into spontaneous remission
What is the prognosis for myasthenia gravis?
-good for recovery if they do not get pneumonia
-40 to 60% mortality overall
What are the characteristics of tick paralysis?
-toxicity that affects the release of Ach
-toxin found in saliva of gravid adult female ticks
What are the clinical signs of tick paralysis?
-weakness beginning in pelvic limbs
-progression to tetraplegia over 12 to 72 hours
-weak/absent spinal reflexes and muscle tone
-can progress to ventilatory failure
How is tick paralysis diagnosed and treated?
-find engorged tick and remove it
-improvement within 24 hours; normal within 72 hours
What are the characteristics of botulism?
-usually a toxicity rather than an infection
-horses > dogs > cats
-toxin localized to cholinergic synapses in PNS
-onset typically within 7 days of ingestion
-severity and onset are dose-dependent
What are the clinical signs of botulism?
-symmetric weakness of all skeletal muscles
-flaccid paresis to plegia of limbs
-resp. muscles possibly affected
-cranial nerves affected
-autonomic signs possible
What are the differentials for botulism?
-fulminant myasthenia gravis
-polyradiculoneuritis
-tick paralysis
How is botulism diagnosed?
finding toxin in blood or GI contents early on
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