L05: Neuromuscular Syndromes (Carrera) Flashcards
Motor Unit
LMN
Neuromuscular jx
Muscle
muscle mass and tone are maintained by:
tonic inputs from the LMN
how quickly does denervation atrophy happen?
rapidly (5-7days)
Common LMN signs
paresis, plegia m. atrophy poor/loss of m. tone weakness to loss of reflexes exercise intolerance paretic, stiff gait ataxia UNLIKELY
Disease that affects nerve root of LMN
Polyradiculoneuritis
Disease process that affects nerve of LMN
polyneuropathies (axon and myelin)
disease processes that affects neuromuscular junction of LMN
tick paralysis
botulism
myasthenia gravis
snakebite
dz proccesses that affects m.
inflammatory
infectious
neoplastic
snakes
chars. of polyradiculoneuritis
- nerve root disorder
- demyelinating
- may require ventilation, supportive care
- mildly delayed nerve conduction velocity
- albuminocytologic dissociation on CSF
CS of polyradiculoneuritis
- acute, ascending flaccid paralysis (MOTOR only)
- loss of reflexes and tone
- cn deficit (cn 7)
- weak gag reflex
- rapid recovery
types of Polyneuropathy
degenerative paraneoplastic endocrine genetic/heritable infectious toxic: vincristine (a microtubule modulator)
CS of degenerative polyneuropathy
- laryngeal paresis/paralysis
- dysphonia
- esophageal dysfx
- esophageal dysfx
- paresis (esp. in PL)
- abn. gait
- common in labs; affects myelin and axons*
Name 3 endocrine neuropathies
Paraneoplastic (ie. insulinoma)
Hypothyroidism
Diabetic neuropathy (cats)
Etiology of Tick Paralysis
-effects NEUROMUSCULAR JX
-presynaptic neuromuscular blockade
-Dermacentor & Amblyomma most common
-Dogs flaccid 5-9d after attachment
+/- megaesophagus
chars. of Tetanus
- effects NEUROMUSCULAR JX
- toxin produced by Clostridium tetani absorbed at the NMJ and travels to spinal cord
- inhibits glycine/GABA release at spinal cord –> constant m. contraction
- cats resistant
CS of Tetanus
stiffness, lockjaw (trismus), sawhorse stance, elevated nictitans, risus sardonicus (grin) 5-10d post infection
Tx of tetanus
- vax only in horses
- tetanus antitoxin
- abx, wound debridement
- sedatives
- supportive care
what is tetany?
hyperexcitability of the membrane due to electrolyte imbalance (is not same as tetanus)
causes of tetany
Na,K,Ca, or Cl- imbalance
hypocalcemia
hypoMg (cows)
strychnine
mech. of botulism
botulinum toxin blocks presynaptic ACh release from the nerve terminal at the NMJ
CS of botulism
-progressive, symmetric ascending paresis/paralysis
-loss of reflexes and tone
-cn 7, megaesophagus, decreased gag and jaw tone
+/- mydriasis, constipation, urinary retention
Dx of Botulism
- detect organism in ingesta, serum, vomit
- neutralization in small rodents
- in vitro test measuring toxin antigenicity
Prognosis of Botulism
-improves in 1-3 wks after motor endplates have regenerated (2-4mo.)
chars. of CONGENITAL Myasthenia gravis
- rare
- generalized weakness since birth
- Jack Russels
- INSUFFICIENT RECEPTORS
- tx ineffective
chars. of ACQUIRED myasthenia gravis
Autoantibodies against nicotinic acetylcholine receptors on the post-synaptic membrane
-receptor blocked –> m. weakness
-3 forms:
Focal (esophageal weakness)
Generalized (exercise intolerance)
Fulminant (25% of generalized patients; grave)
-usually immune mediated in younger dogs and neoplastic in older dogs
CS of myasthenia gravis
- exercise intolerance
- postural rxns INTACT
- reflexes present but withdrawal may be slow
- NO cn deficits
- megaesophagus
Dx of myasthenia gravis
- Tensilong test using ultra-short acting AChE inhibitor (think video)
- ACh receptor Ab titer
- Electrodiagnositcs: repetitive nerve stimulation
Tx of myasthenia gravis
AChE inhibitor (increases ACh at the NMJ)
Immunosuppression (stops Ab production)
Tx underlying dz
Causes of generalized myopathy
immune-mediated infectious (neospora caninum) pre/para-neoplastic (lymphoma) dermatomyositis congenital (m. dystrophies
Chars. of generalized Polymyositis
- generalized weakness, stilted gait, dysphagia, m. atrophy
- Do NOT lose reflexes
- Boxers, Newfies
Chars. of Masticatory myositis
-AutoAb to Type 2M variant muscle fibers, but only expressed in masticatory muscles
-Acute and chronic forms:
acute: pain on opening mouth, mild exophthalmia
chronic: masticatory m. atrophy and fibrosis, can’t open
mouth
Dx of masticatory myositis
serum 2M antibody titer (Gold Standard!)
Tx of masticatory myositis
immunosuppression
consider m. biopsy for prognosis
extraocular myositis
- can’t move eyes
- bilateral ventromedial strabismus
- tx same as masticatory myositis
CS of Neospora caninum
- polyradiculoneuritis and polymyositis
- m. atrophy
- contracture of PLs
which myofibers more affected by endocrine myopathies?
Type 2
Endocrine myopathy causes
Hypo (dogs) or Hyperthyroidism (cats) Glucocorticoid excess (dogs) Electrolyte derangements
CS of Hyperthyroidism-induced myopathy in cats
- paresis
- cervical ventroflexion
- tremors
- abnormal gait
Toxoplasma gondii can also cause feline myopathy
:)
CS of snake envenomation
mentation, paresis/plegia, rigidity, CP defitis
Diamondbacks venom mech.
Myokymia - Ca interference on nerve membrane
Mojave rattlesnake venom mech.
toxin inhibits Ach release at the presynaptic terminal of the NMJ leading to complete neuromuscular blockade
Mech. of coral snake venom
- postsynaptic alpha-neurotoxins
- neuromuscular blockade
- generalized LMN weakness –> resp. paralysis
name 3 congenital myopathies
muscular dystrophy (Goldens)
myotonia congenita
hyperkalemic periodic paralysis (horses)
Exercise Induced Collapse
- labs
- collapse, marker hyperthermia during episode but otherwise normal
- dx of exclusion
- cause: DNM1 mutation (gene involved in neurotransmission,etc.)
myoclonus
sudden contraction-relaxation of muscles
-assoc. with distemper
