Lecture: Neuromuscular Syndromes Flashcards
Motor unit
- Lower Motor Neuron
- Neuromuscular Junction
- Muscle
Maintenance of motor unit
- Maintenance by tonic inputs from LMN
Denervation atrophy
rapid and severe (5-7 days)
LMN signs
- Paresis to plegia
- Muscle atrophy
- poor/loss muscle tone
- weakness to loss of reflexes
- exercise intolerance
- paretic, stiff gait
Ataxia and LMN dz
- ataxia is an ulikely sign of LMN dz
LMN DZs
Tetanus
Happens at level of spinal cord
DZs of LMN
Nerve root
Polyradiculoneuritis
DZs of LMN
Nerve
- (poly)Neuropathies
- Axon
- Myelin
DZs of LMN
Junction
- Tick Paralysis
- Botulism
- Myasthenia Gravis
- Snakes
DZs of LMN Muscle
- Inflammatory
- Infectious
- Neoplastic
- Snakes
Polyradiculoneuritis
Coonhound Paralysis, Guillan-Barre syndrome
- Poly = multiple
- Radiculo = root
- Neuritis = inflammation of the nerve
Polyradiculoneuritis
About
- Racoon saliva?
- Demyelinating dz - rapid recovery
- can get distal axonal degeneration
- Root & proximal nerve disorder
- mildly delayed nerve conduction velocity (NCV)
- Albuminocytologic dissociation on CSF
Polyradiculoneuritis
CS
- Acute, ascending flaccid paralysis
- LOSS of reflexes and tone
- motor, not sensory
- atrophy
- CN deficits common
- CN VII, gag
Polyradiculoneuritis
TX
- Variable dz course
- may require ventilation
- supportive care
- aggressive physical therapy to avoid joint fibrosis
Polyneuropathy
- Degenerative
- Paraneoplastic
- Endocrine
- Genetic/heritable
- Infectious
- Toxic: Vincristine (microtubule disruptor)
Degenerative Polyneuropathies
Labrador retrievers
- 10+ yo
- Laryngeal paresis/paralysis
- Dysphonia (bark change)
- Esophageal dysfunction
- Paresis worse in pelvic limbs
- abnormal gait
*affects myelin & axons
Inherited polyneuropathy
Leonbergers
Endocrine Neuropathies
- Paraneoplastic - insulinoma
- Hypothyroidism
- Diabetic neuropathy - feline
- plantigrade posture
Tick Paralysis
- Presynaptic neuromuscular blockade
- Dermacentor & Amblyomma most common
- Dogs flaccid 5-9 days after tick attachement
- cats resistent
- +/- megaesophagus
- In Australia
- Ixodes holocyclus, Argasid ticks
- MUCH Worse
Tetanus
about
- Tetanospasmin must be cleaved to be activated
- absorbed at the NMJ and travels retrograde to spinal cord
- Inhibits glycine/GABA release at SPINAL CORD
- leads to hyperactive alpha motor neurons = constant muscle contraction
Tetanus
CS
- 5-10 days after infection
- increased tone, stiffness, risus sardonicus, elevated tail, sawhorse stance, elevated nictitans
- Extensors are stronger than flexors
- external stimuli may exacerbate spasticity
Tetanus
TX
- Vaccination
- Tetanus toxoid in horses
- Antitoxin
- Antibiotics and wound debridement
- penicillin G, tetracycline, metranidazole
- Sedatives
- Phenothiazines, benzodiazepines, barbiturates
- Supportive care
- dark, quit, well padded, feeding tube
Tetany
- Hyperexcitability of membrane due to electrolyte imbalance
- Na+, K+, Ca+, Cl-
- Hypocalcemia
- Hypomagnesemia
- Strychnine
Botulism
about
- Presynaptic neuromuscular blockade
- Ingest preformed toxin
- destroyed at 100 degrees
- resistant to proteases
- Toxin imported, blocks presynaptic release of ACh from nerve terminal
Botulism
CS
- 12 hrs-6 days
- progressive, symmetric ascending paresis/paralysis
- reflexes and tone are lost
- CN VII, megaesophagus, decreased gag and jaw tone
- +/- mydriasis, KCS, constipation, urinary retention
Botulism
DX
- Very difficult
- detection of organism in ingesta, serum, vomit
Botulism
Prognosis
- Improvement in 1-3 weeks
- must regenerate new motor endplates
- 2-4 months in mammalian species
Myasthenia Gravis
Congenital
- Insufficient receptors
- Negative AChRAb titer
- rare
- jack/parsons russel terriers
- signs from birth
- generalized weakness
Myasthenia Gravis
Acquired
- Autoantibodies against nicotinic acethylcholine receptors on post-synaptic membrane
- receptor is blocked, causing muscle weakness
Acquired Myasthenia Gravis
three forms
- Focal: typically esophageal muscle weakness
- dogs only; cats have smooth muscle
- Generalized: exercise intolerance
- Fulminant: 1/4 of the generalized patients
- Grave
Myasthenia Gravis
CS
- Exercise intolerance
- progressively stiff, stilted gait, crap walking, crouched
- Postural rxns should be intact
- Reflexes present/ withdrawels can tire
- No CN deficits
- may have weak gag, ptyalism, ptosis
- Megaesophagus
Acquired Myasthenia Gravis
Distribution
- Bimodal
- osteosarc is also bimodal
- < 5 yrs old: immune mediated
- > 7 yrs old
- para/pre-neoplastic
- treat/remove primary source to ease tx
Myasthenia Gravis
DX
- Tensilon test: edrophonium
- ultra-short acting acetylcholinesterase inhibitor
- Acetylcholine receptor antibody titer (GOLD STANDARD)
- Electrodiagnostics: repetitive nerve stimulation (RNS)
Myasthenia Gravis
TX
- Acetylcholinesterase inhibitor
- increases ACh at the NMJ
- Immunosuppression
- stops Ab production
- Treatment of underlying dz
- eliminates trigger
Generalized Myopathy
- Immune-mediated
- Infectious
- neospora caninum, Hepatozoon americanum
- Pre-/Para-neoplastic
- lymphoma
- Dermatomyositis
- Congenital
- muscular dystrophies
Generalized polymyositis
- Generalized weakness, stilted gait, dysphagia, muscle atrophy
- Myalgia is rare
- DO NOT LOSE REFLEXES
- Boxers and Newfies
- Boxers: preneoplastic
- Newfies: breed specific
Masticatory myositis
DX
Acute
Chronic
TX
Type 2M and Type 1 variant muscle fibers
- Autoantibodies to type 2M fibers (only expressed in masticatory mm)
Serum 2M antibody titer (easy dx)
Acute
- pain opening mouth
- mild exophthalmia
Chronic
- masticatory m atrophy
- not painful to open mouth
- fibrosis of masticatory mm
TX
- immunosuppression
Extraocular Myositis
Acute phase: ze eyeballz don’t move
Neospora caninum
- Prenatal exposure
- Polyradiculoneuritis and polymyositis
- encephalomyelitis
- Muscle atrophy
- Contracture of Pelvic Limbs
*Spay the mom
Endocrine Myopathies
- Type 2 myofibers more affected
- Hypothyroidism-dogs
- Hyperthyroidism-cats
- Glucocorticoid excess-dogs
- Electrolyte derangements
Cushing’s Myopathy
Stiff, not flexing, hypertrophic, stiff muscles
Cat anatomical anomaly
No nuchal ligament
Feline Hyperthyroidism
- T3 & T4 effects on sarcoplasm
- CS
- Paresis
- ventroflexion
- tremors
- abnormal gait
Feline: Toxoplasma gondii
Brain and systemic infection
Rattlesnake Envenomation
(pit vipers)
- Mentation, paresis/plegia, rigidity, CP deficits
Southern Pacific, Timber, Western Diamondback envenomation
- Myokymia
- Ca interference on nerve membrane
- looks like a moving nerve under skin I think
Mojave rattlesnake envenomation
- Neurotoxins
- inhibits Ach release at presynaptic terminal of NMJ leading to complete neuromuscular blockade
Coral Snake envenomation
(Elapid snake)
- Venom has many components
- postsynaptic alpha-neurotoxins
- neuromuscular blockade
- Generalized LMN weakness
- respiratory paralysis
Congenital myopathies
- Muscular dystrophy: golden retrievers
- Myotonia congenita
- Hyperkalemic periodic paralysis
Exercise Induced Collapse
- labrador retrievers
- collapse, hyperthermia, loss patellar reflexes
- DNM1 mutation
Myoclonus
- Sudden contraction-relaxation of muscles
- LMN abnormality
- Distemper
