Principles of neuromuscular disease Flashcards
What are some common physical examination findings of neuromuscular disease?
Gait abnormalities as either paresis or ataxia
Muscle loss
Altered respiratory effort or inspiratory stridor
What is the typical history of an animal with neuromuscular disease?
Weakness, difficulty rising, exercise intolerance, altered voice, change in musculature, regurgitation and lameness or pain
What are some common neurological examination findings of neuromuscular disease?
Tetraparesis +/- proprioceptive ataxia
Muscle atrophy or pain
Reduced spinal reflexes and muscle tone
Sensory deficits or self mutilation (chew feet)
What is also seen if there is an autonomic neuropathy?
Dilated pupils, decreased tear production, hyposalivation, bradycardia, constipation, urinary retention and reduced perianal reflex
What diagnostic tests should be performed if neuromuscular disease is suspected?
Biochemistry, haematology, urinalysis for CK, glucose, electrolytes and cholesterol, AChR antibodies or endrophonium response test (myasthenia gravis), Endocrine testing for hyperthyroidism or hyperadrenocorticism, Serology for neospora or toxoplasma, Imaging for neoplastic disease, CSF analysis to test nerve roots and CNS, Nerve and muscle biopsy to look for infection, endocrinopathy, denervation or infection, Metabolic tests for lysosomal storage disease, Genetic tests for Labrador myopathy or other inherited diseases
What gait abnormalities are seen with neuromuscular disease?
Paresis +/- ataxia Frequent sitting down Exercise intolerance Low head carriage Hypometria
What does electrophysiology tell you?
Localisation of nerve/muscle/junction
Myelin/axon
Specific nerves or muscles affected
What is an EMG?
Electromyogram
Normally silent and performed with needle electrodes under anaesthesia
What do fibrillation potentials indicate?
Denervation and inflammation
What are the characteristics of fibrillation potentials?
Biphasic
Sound like frying eggs/rain on a tin roof
Spontaneous action potentials of single myofibres
What do positive sharp waves indicate?
Denervation
What are the characteristics of positive sharp waves?
Positive deflection followed by shallow negative deflection
Sound like a dull thud/racing car driving by
Due to spontaneous action potentials of single myofibres
What are the characteristics of complex repetitive discharges?
Polyphasic
Serrated each one with a uniform shape
Sounds like a machine gun
What causes complex repetitive discharges?
Many myofibres firing in near synchrony
What is a pseudomyotonia on an EMG?
Myotonic potential with waxing and waning amplitude and frequency due to independent, repetitive discharges of singled, injured myofibres,
Unusual and sounds like a revving moped/chainsaw
How is a Motor Nerve Conduction Velocity (MNCV) calculated?
Distance (m) over proximal latency (b) minus distal latency (a)
Stimulate nerve in two sites and calculate velocity between them
What else can you measure using electrophysiology?
F-waves or Brainstem Auditory Evoked Potentials (BAEP)
How useful is electrophysiology?
Definitive evidence of neuromuscular function
Differentiate between nerve and muscle
Tell extent and severity of damage
Provides a method to monitor treatment
Give a prognosis and allows clinician to know exactly which muscles/nerves are affected
What is the common signalment of acquired myasthenia gravis?
Animals over 3 months
Predisposed in GSD, Labradors and Golden Retrievers
What are the three forms of acquired myasthenia gravis?
Focal with megaoesophagus/regurgitaion in 30% of dogs
Generalised with exercise intolerance and megaoesophagus which occurs in 60% of dogs
Fulimating form
What is the pathophysiology of acquired myasthenia gravis?
ACh receptor reduction due to antibodies binding to them making it an immune mediated disease
How is acquired myasthenia gravis diagnosed?
Edrophonium chloride (Tensilon test)
Serology
Check for paraneoplastic syndromes associated with thymus
What is the treatment and prognosis for acquired myasthenia gravis?
Pyridostygmine +/- immunomodulatory drugs
Why do you need to take care when using edrophonium chloride?
Can cause a cholinergic crisis
What is the signalment of dogs with congenital myasthenia gravis?
6-8 weeks old
Jack Russels, Springer Spaniels and Miniature Dachshunds predisposed
What are the clinical signs of equine botulism?
Flaccid paralysis due to ingestion of beta toxin produced by Clostridium botulinum which inhabits the soil
What is the pathogenesis of equine botulism?
Toxin irreversibly blocks the release of ACh at the NMJ
Outbreaks due to contaminated feed
What happens in the rarer form of equine botulism?
Toxico-infections in young foals where spores are ingested and the organism proliferates in the intestine or wound
What are the clinical signs of equine botulism?
Dysphagia, reduction in tail/tongue/eyelid tone, generalised weakness, recumbency, muscle fasciculations, pupillary dilation, ileus and respiratory paralysis
What is the treatment for equine botulism?
Antibiotics for pneumonia
Fluid therapy
Nutrition
Recumbent horse management
What is the prognosis of equine botulism?
Guarded unless caught early
What does neuropathic syndrome affecting motor nerves result in?
LMN signs
What signs happen if sensory nerves are affected by neuropathic syndrome?
Hypoalgesia, hypoaesthesia, CP deficits, self-mutilation, reduced reflexes, no atrophy
What happens if autonomic nerves are affected by neuropathic syndrome?
Pupillary changes, decreased tear production, decreased salivation and bradycardia
What peripheral neuropathies are seen in large animals?
Femoral nerve paresis in calves born breached due to pulling out
Obturator nerves in cows and horses after giving birth
Brachial plexus injury
Radial nerve paralysis
Suprascapular nerve damage with muscle atrophy of supra and infraspinatus
What does myopathic syndrome result in?
Paresis, exercise intolerance, gait still and stilted, muscle atrophy or hypertrophy, muscle pain on palpation
