Neuromuscluar Disease Flashcards
The motor unit consists of what 3 things?
Lower motor neuron, neuromuscular junction, and muscle
What are common LMN signs?
- Paresis to plegia
- Muscle atrophy
- Poor/loss of mm tone
- Weakness to loss of reflexes
- Exercise intolerance
- Paretic, stiff gait
T or F: with LMN Disease, you will typically see ataxia
False; typically LMN disease has MOTOR manifestations and doesn’t affect your sensory tracts
What is polyradiculoneuritis?
- Also known as coonhound paralysis (Guillan-Barre syndrome in people)
- Multiple root inflammatory dz that causes acute, ascending flaccid paralysis (LOSS of reflexes and tone, motor, not sensory > atrophy)
- CN deficits often seen (VII, gag)
- May require ventilation, supportive care
If you have the demyelinating version of polyradiculoneuritis, what is your prognosis?
- Rapid recovery - can get distal atonal degeneration
- Mildly delayed NCV
- Root and proximal nerve disorder - abnormal F waves
- Albuminocytologic dissociation on CSF (high protein in the face of a low cell count)
What are your differential causes for polyneuropathy?
- Degenerative
- Paraneoplastic
- Endocrine
- Genetic/heritable
- Infectious
- Toxic: Vincristine
Describe clinical signs of degenerative polyneuropathies
- Typically in Labs <10 yrs
- Laryngeal paresis/paralysis
- Dysphonia
- Esophageal dysfunction
- Paresis, worse in pelvic limbs
- Abnormal gait
What is sciatic release and what condition might you see this with?
Sciatic nerve is dysfunctional and cannot counter the femoral nerve’s effects, so patient will appear to lack sciatic tone and soldier step with degenerative polyneuropathies
What are 3 endocrine polyneuropathies?
Paraneoplastic - insulinoma
Hypothyroidism
Diabetic neuropathy - feline
Leonbergers are unique with their polyneuropathy cause, what makes them different?
Their degenerative polyneuropathies have a familial component - there’s a genetic test to determine if they have it
What types of ticks cause tick paralysis and what is the mechanism behind it?
- Dermacentor and Amblyomma
- Ixodes, Argasid in Australia - MUCH worse - need antitoxin
- Causes presynaptic neuromuscular blockade
- dogs flaccid 5-9 days after tick attaches (cats resistant)
- +/- megaesophagus
- Tx with Frontline
What is the MOA of tetanus?
- Clostridium tetani produces tetanospasmin - must be cleaved to be activated and internalized
- Tetanospasmin absorbed at the NMJ and travels retrograde to SC
- Inhibits glycine/GABA at the spinal cord leading to hyperactive alpha motor neurons and constant muscle contraction
What are the clinical signs of tetanus?
- 5-10 days after infection
- Increased tone, stiffness, risus sardonicus, trismus (active contraction of jaw), elevated tail, sawhorse stance
- External stimuli may exacerbate spasticity
What is your treatment for tetanus?
- Vaccination - tetanus toxoid (horses)
- Neutralize circulating toxin - antitoxin
- Abx and wound debridement
- it all started with a bacterial infection
- Sedatives
- Supportive care
What other things can cause tetany?
- Hyperexcitability of the membrane due to electrolyte imbalance
- Na, K, Ca, Cl
- Hypocalcemia
- HypoMg
- Strychnine
What are the effects of botulism and how does it get into the system?
- Clostridium botulinum cause presynaptic neuromuscular blockade when animal ingests the preformed toxin (types A-H, C most common)
- toxin is imported, then blocks presynaptic ACh release from the nerve terminal
What are the clinical signs of botulism and how does one diagnose it?
CS:
- 12hrs - 6d
- Progressive
- symmetric ascending paresis/paralysis
- Reflexes and tone are lost
- CN VII, megaesophagus, decr gag and jaw tone
- +/- mydriasis, KCS, constipation, urinary retention
Dx: detection of organism in ingesta, serum, vomit, neutralization in rodents, in vitro measuring toxin antigenicity
What is your prognosis for botulism and why does it take this long?
- Improvement in 1-3 weeks
- must regenerate new motor endplates (2-4 mo in mammals)
What are the effects of congenital myasthenia gravis and what breed typically get it?
- Rare condition in Jack and Parsons Russell terriers that have signs from birth and generalized weakness due to insufficient receptors
- CS: neg AChRAb titer
What is the MOA of acquired myasthenia gravis?
Autoantibodies against nicotinic acetylcholine receptors on the post-synaptic membrane
- Your receptor is blocked, causing muscle weakness
What are the three forms of acquired myasthenia gravis?
- Focal - typically esophageal mm weakness (only in dogs!, cats have smooth mm)
- Generalized - exercise intolerance
- Fulminant - 1/4 of the generalized patients, grave prognosis
What are the clinical signs of myasthenia gravis?
- Exercise intolerance - progressively stiff, stilted gait, crab-walking, crouched
- Postural reactions should be intact
- Reflexes present, though withdrawals can tire
- No CN deficits - can have weak gag, ptyalism, ptosis
- Megaesophagus
Acquired myasthenia gravis has a bimodal distribution, what two groups does it tend to affect?
- <5 yr old - immune mediated
- <7 yr old - para/pre-neoplastic
- treat/remove primary source to make tx easier
How do you diagnose myasthenia gravis?
- Tensilon test: edrophonium, ultra-short acting AChE inhibitor
- ACh receptor Ab titer - gold standard (dog or cat)
- Electrodiagnostics - respective nerve stimulation (RNS): positive decrement
What are the treatments for myasthenia gravis?
- AChE inhibitor - incr ACh at the NMJ
- Immunosuppression - stops Ab production
- Tx underlying dz - eliminates trigger
What are your differentials for causes of generalized myopathy?
- Immune-mediated
- Infectious - Neospora caninum, Hepatozoon americanum
- Preneoplastic - lymphoma
- Dermatomyositis
- Congenital - muscular dystrophies
What are the clinical signs of generalized polymyositis and what breeds are commonly represented?
- CS: Generalized weakness, stilted gaits, dysphagia, muscle atrophy, myalgia is rare
- do NOT lose reflexes
- Boxers (preneoplastic) and Newfies (breed specific)
What is mastication myositis and how do you diagnose it?
- Get neutrophilic inflammation of Type 2M and Type 1 variant muscle fibers
- VERY painful > autoantibodies to type 2M fiber, ONLY expressed in masticatory muscles!
- Dx with serum 2M antibody - very sensitive/specific
What are the clinical signs of masticatory myositis?
Acute: pain on opening mouth, mild exophthalmia
Chronic: masticatory muscle atrophy, non-painful inability to open mouth, fibrosis of masticatory muscles
How do you treat masticatory myositis?
Early and aggressive tx - immunosuppression
If chronic and severe atrophy and trismus, consider muscle biopsy for prognosis
What are the effects of extraocular myositis and how is it treated?
Animals can become effectively blind due to inflamed extraocular muscles; treated the same way as masticatory myositis
How does one get polymyositis from Neospora caninum and what are the effects?
Prenatal exposure
- CS: polyradiculoneuritis and polymyositis - encephalomyelitis, muscle atrophy, contracture of PLs
What are examples of endocrine myopathies and what fibers are most affected?
- Hypothyroidism - dogs
- Hyperthyroidism - cats
- Glucocorticoid excess (endogenous/exogenous) - dogs
- Electrolyte abnormalities
*Type 2 myofibers more effected
What are the two most common feline myopathies and what are the signs?
- Hyperthyroidism
- paresis
- ventroflexion
- tremors
- abnormal gait
- T3 and T4 effects on sarcoplasm
- Toxoplasma gondii - brain and systemic infection
What is the effect of coral snake envenomation on the muscles?
- Venom components:
- Postsynaptic alpha neurotoxins
- neuromuscular blockade
- Generalized LMN weakness - resp paralysis
What are 3 congenital myopathies?
- Muscular dystrophy - Golden retrievers
- Myotonia congenital - mini Schnauzers
- Hyperkalemia periodic paralysis (HYPP) - quarter horses
What is myoclonus and what is it commonly seen with?
Sudden contraction-relaxation muscles, commonly seen with distemper
