Neuromuscular disorders Flashcards
Peripheral nerves
12 pairs of cranial nerves and 36 pairs of spinal nerves
Contain both motor and sensory axons
Limbs supplied by nerves from brachial or lumbosacral plexi
Neuromuscular juntion
Axon terminal, a synaptic cleft, and the endplate region of skeletal muscle
Junction is a transducer (electrical to chemical)
Clinical signs of muscle/nerve/synapse dysfunction
Generailsed weakness
Split into neuropathies, myopathies, and juctionopathies
Clinical signs of neuropathies
LMN disease
Usually severe impairment of motor function
Gait: Flaccid paresis or paralysis
Postural reaction: deficits
Spinal reflexes: Reduced/absent
Muscle tone: decreased to absent
Muscle mass: neurogenic muscle atrophy
Sensation: Decreased (hypoesthesia) to absent (anaesthesia). Paraesthesia, auto-mutilation
Cranial nerve deficits: V, VII, IX, X/XI, dysphagia, dysphonia, regurgitation due to megaoesophagus
Clinical signs of myopathies
Ventroflexion of the neck - especially in cats
Gait: generalised weakness, exercise intolerance, stiff and stilted
Postural reactions: usually normal
Spinal reflexes: usually normal
Muscle tone: usually normal
Muscle mass: muscle atrophy
Sensation: Usually unaltered, but can have muscle pain on palpation
Cranial nerve deficits: Usually unaltered but may be altered by involvement of masticatory muscles or impairment of swallowing
Neuromuscular diagnostic investigation (NM)
Haematology
Serum biochem (creatinine kinase and electrolytes)
Urinalysis (glucosuria, myoglobinuria)
Chest x-rays (megaoesophagus, aspiration pneumonia)
Peripheral nerve disorders causing generalised weakness
Idiopathic polyradiculoneuritis
Protozoal neuritis-myositis
Diabetes
Muscle diseases causing generalised weakness
Protozoal neuritis-myositis
Polymyositis
Hypokalaemia
Neuromuscular diseases causing generalised weakness
Myasthenia gravis
Botulism
Organophosphate and carbamates
Infectious causes of nerve/muscle ‘generalised weakness’
Protozoal polyradiculoneuritis-myositis
Inflammatory causes of nerve generalised weakness
Idiopathic polyradiculoneuritis
Inflammatory causes of muscle generalised weakness
Idiopathic polymyositis
Inflammatory causes of NM junction generalised weakness
Myasthenia gravis
Indiopathic causes of muscle generalised weakness
Exercise induced rhabdomyolysis
Toxic causes of nerve generalised weakness
Vincristine
Toxic causes of Muscle generalised weakness
Toxic rhabdomyolysis
Toxic causes of muscle generalised weakness
Botulism, organophosphates/carbamates, aminoglycosides
Metabolic causes of nerve generalised weakness
Diabetes mellitus
Hypothyroidism
Metabolic causes of muscle generalised weakness
Cushing’s myopathy
Hypothyroidism
Hypoadrenocorticism
Hypokalaemic myopathy
Neoplastic causes of nerve generalised weakness
Paraneoplastic: insulinoma
Neoplastic causes of muscle generalised weakness
Paraneoplastic: lymphoma
Neoplastic causes of NM junciton generalised weakness
Paraneoplastic
Degenerative causes of nerve generalised weakness
Inherited neuropathies
Degenerative causes of muscle generalised weakness
Inherited myopathies
Degenerative causes of NM junction generalised weakness
Myasthenia congenita
Pathogenesis of idiopathic polyradiculoneuritis
Signs caused by immunemediated attach to the axons and myelin sheaths at level of ventral nerve roots
Epidemiology of idiopathic polyradiculoneuritis
Most common peripheral neuropathy
Clinical signs of of idiopathic polyradiculoneuritis
Start acutely in the pelvic limbs
Rapidly progress to LMN tetraparesis or tetraplegia
DIfferential diagnosis of idiopathic polyradiculoneuritis
Looks very similar to Botulism, but in botulism the cranial nerve deficits are more prominent
Diagnosis of idiopathic polyradiculoneuritis
Electromyography reveals denervation potentials
Nerve conduction velocities are reduced
CSF can show an increase in mononuclear cells.
Bloods (serology neospora exclusion)
Prognosis of idiopathic polyradiculoneuritis
Outcome is good - recover over a period of 3-6 weeks
Treatment of idiopathic polyradiculoneuritis
Supportive care and rehabilitation
Corticosteroid administration is not beneficial
Monitor pulmonary function
Pathogenesis of myasthenia gravis
Failure of NM transmission due to reduction in number of functional nicotinic actylcholine receptors
An immune-mediated disease caused by an over-production of antibodies directed against acetylcholine receptors
Epidemiology of myasthenia gravis
Relatively common in dogs
Relative rare in cats
Usually occurs spontaneously
Can be associated with thymoma or other neoplastic/immunemediated diseases
Clinical signs of myasthenia gravis
Focal: facial, oesophageal, laryngeal, and pharyngeal weakness, resulting in regurgitation and dysphagia
Generalised: exercise intolerance, regurgitation, stiff gait with short strides
Acute fulminant form of generalised: very rapid onset or paralysis and regurgitation - rare
Diagnosis of myasthenia gravis
Resolution of muscle weakness following IV injection of edrophonium chloride
Repetitive nerve stimulation- decremention of the action potential
Serum sample: ACh antibodies
Chest x-ray for cranial mediastinal mass
Prognosis of myasthenia gravis
Good
Clinical remission is 6 months
Guarded if persistent megaoesophagus
Treatment of myasthenia gravis
ACh inhibitors
- pyridostygmine
- neostigmine in case of severe regurgitation
Immunosuppressive therapy
- steroids
- controversial
Neuromuscular diseases causing ‘focal weakness’
Aortic thromboembolism
Masticatory myositis (muscle)
Brachial plexus avulsion
Sciatic nerve injury
Nerve sheath tumour
Pathogenesis of aortic thrombosis
Obstruction of aortic or iliac arteries
Common underlying cause: hypertrophic cardiomyopathy
Restriction of blood flow by embolus causes ischaemia to the sciatic nerve and muscles of the pelvic limbs
Epidemiology of aortic thrombosis
Most commonly seen in cats
Clinical signs of aortic thrombosis
Acute onset of pelvic limb paresis/plegia,
loss of pelvic limb nociception distally,
Weak or absent femoral pulse
Cold limbs
Cyanotic nail beds
Very painful
Signs of heart failure may be present
Diagnosis of aortic thrombosis
Based on clinical signs
Marked elevated serum CK present in first 1-2 days
Chest x-rays and echocardiography - evidence of cardiac disease
Prognosis of aortic thrombosis
Long term prognosis poor - association with heart disease
Worth treating if pain can be controlled
Treatment of aortic thrombosis
Management of cardiac disease
Low dose aspirin to prevent further blood clots - controversial
Pain relief is mandatory
Pathogenesis of (malignant) peripheral nerve sheath tumours
Aggressive biological behaviour
Most commonly affects the caudal cervical (C6-C8) and cranial thoracic (T1-T2)
Spread slowly
May invade vertebral canal causing spinal cord compression
Highly invasive locally but rarely metastasize
Epidemiology of (malignant) peripheral nerve sheath tumours
Brachial plexus tumours are seen in adult, older dogs.
Cats will rather have a lymphoma of the brachial plexi
Clinical signs of (malignant) peripheral nerve sheath tumours
Slowly progressive thoracic lameness, paresis and muscle atrophy
Pain on palpation of the axillary region
Axillary mass may be palpable
Ipsilateral partial or complete Horner’s syndrome, and ipsilateral absent cutaneous trunci reflex
Diagnosis of (malignant) peripheral nerve sheath tumours
Diagnosis by exclusion of orthopaedic disease and radiographs of thoracic limbs.
Electromyogram shows abnormal and spotnaeous muscle activity
Chest x-rays and abdominal ultrasound performed to metastatic disease
MRI of brachial plexus or peripheral nerves can visualise the nerve root tumour
Prognosis of (malignant) peripheral nerve sheath tumours
Poor with high recurrence rate after surgery (amputation)
Treatment of (malignant) peripheral nerve sheath tumours
Local excision is rarely possible; usually leg amputation with or without spinal decompression is needed
Pathogenesis of brachial plexus trauma
Usually caused by a road traffic accident or fall from height - abduction and caudal displacement of thoracic limbs
Site of avulsion is usually intradural
Epidemiology of (malignant) peripheral nerve sheath tumours
Most common cause of acute thoracic limb monoparesis/plegia in small animals
Clinical signs of (malignant) peripheral nerve sheath tumours
Peracute onset of monoparesis/plegia following traumatic incident
Avulsions
Ipsilateral partial Horner’s syndrome and/or loss of cutaneous trunci reflex
Three types of avulsion
Cranial avulsions (C6-7) - rare, few clinical signs
Caudal (C8-T2) or Complete (C6-T2)
- more common
- more severe clinical signs
- paralysis of brachial triceps
Diagnosis of (malignant) peripheral nerve sheath tumours
Acute history of a traumatic incident
Electromyogram allows detection of spontaneous electrical activity in denervated muscles 7-10 days after injury
Prognosis of (malignant) peripheral nerve sheath tumours
Most cats still have pain sensation on presentation, compared to dogs
Prognosis is good if deep pain sensation is present
If deep pain absent, prognosis will depend on the severity of the axonal injury
Treatment of (malignant) peripheral nerve sheath tumours
No routinely effective treatment
Amputation of limb may be needed but wait 2-3 months to see if recovery occurs
