Weakness and principle of neuromuscular disease

Question 1

What are the 3 areas that can be affected in the neuromuscular system?

Answer 1

LMN nerves: neuropathy
neuromuscular junctions NMJ: junctionopathy
Skeletal muscle: myopathy

Question 2

When should we suspect neuromuscular disease?

Answer 2

weakness (generalised or focal)
exercise intolerance (walks normal then progressively weak/stiff)

Question 3

What is an important clinical sign suggestive of neuromuscular disease in cats?

Answer 3

cervical ventroflexion
myopathy

not seen in dogs due to passive support from the nuchal ligament (not present in cats)

Question 4

What others systems could cause weakness?

Answer 4

cardiovascular
respiratory
systemic/metabolic
neuro

Question 5

What could make us suspicious that weakness is from CVRS? What dx tests can help confirm this?

Answer 5

Hx: cough, CHF
PEx: murmur, arrhythmia, pulse quality

Dx tests: bp, ecg, thoracic radiographs, echocardiography, cardiac troponin 1

Question 6

What could make us suspicious that weakness is from systemic/metabolic? What dx tests help confirm this?

Answer 6

Hx/PEx: pale mm, pyrexia, distended abdomen

Dx tests: haematology, serum biochem, electrolyte analysis, blood gas analysis, abdomen/thorax ultrasound

Question 7

What electrolytes can affect weakness?

Answer 7

hypokalaemia: hypokalaemic myopathy
hypocalcaemia: puerperal tetany/eclampsia

Question 8

What would make us suspicious that weakness is from neuro?

Answer 8

is the patient neuro normal or abnormal?
what is the neuroanatomical location?

• mentation not affected by neuromuscular dz
• nociception is a sensory process, also not in neuromuscular disease

Question 9

What clinical signs in weak animals (esp. dogs) raises suspicion for neuromuscular disease?

Answer 9

regurgitation! (make sure not vomiting aka passive after eating)
can be important CS for megaoesophagus

dysphonia: loosing bark especially with progressive weakness

paresis with minimal ataxia

palmigrade/plantigrade

inatct/mildly reduced postural reaction when weight supported

reduced spinal reflexes

focal or generalised muscleatrophy

Question 10

What are the clinical signs for neuropathy specifically?

Answer 10

reduced to absent spinal reflexes
plantigrade/palmigrade stance
reduced to absent muscle tone

+/- neurogenic muscle atrophy

Question 11

What are the clinical signs of a junctionopathy specifically?

Answer 11

normal to reduced spinal reflexes
exercise intolerance (may be normal on examination prior to exercise)

Question 12

What are the clinical signs of a myopathy specifically?

Answer 12

often normal spinal reflexes
exercise intolerance
cervical ventroflexion in cats

+/- myalgia, muscle atrophy/hypertrophy

Question 13

What diagnostic tests allow us to know its likely a myopathy vs neuropathy or junctionopathy?

Answer 13

muscle enzymes: elevated CK, AST, ALT
urinalysis: myoglobinuria

Question 14

What does electromyography EMG tell us?

Answer 14

functional test
if electrically silent at rest: normal muscle or disuse atrophy
spontaneous electrical activity: neuropathy or myopathy

Question 15

What does decreased amplitude on nerve conduction studies indicate?

Answer 15

axonal disease: neuropathy

Question 16

What does slowed conduction velocity on nerve conduction studies indicate?

Answer 16

myelin disease: neuropathy

Question 17

What does decremental response on repetitive nerve stimulation in nerve conduction studies indicate?

Answer 17

myasthenia gravis: junctionopathy

Question 18

What are the 4 groups of neuromuscular differential diagnoses?

Answer 18

acute generalised
chronic generalised
acute focal
chronic focal

Question 19

What are the most common acute generalised neuromuscular diseases?

Answer 19

infl.: acute canine polyradiculoneuritis

idiopath/paraneoplastic: acquired myasthenia gravis

toxic: botulism, tick paralysis, pesticides, drugs

metabolic: hypocalcaemia, hypokalaemia, hyperadrenocorticism, exertional rhabdomylysis

Question 20

see acute canine polyradiculoneuritis slide

Question 21

see acquired myasthenia gravis slide

Question 22

What are the most common chronic generalised neuromuscular diseases?

Answer 22

degenerative: inherited/breed polyneuropathy

metabolic: diabetic polyneuropathy, hypokalaemia

infl.: chronic inflammatory demyelinating polyneuropathy, immune-mediated polymyositosis

infectious: neospora

idiopathic/paraneoplastic: myasthenia gravis

other: centronuclear myopathy, muscular dystrophy, myotonia congenita

Question 23

see centronuclear myopathy slide

Question 24

What are the most common acute focal neuromuscular diseases?

Answer 24

idiopathic/paraneoplastic: trigeminal neuropathy, facial neuropathy, myasthenia gravis focal

trauma: brachial plexus avulsion, femoral/sciatic nerve injury, tail pull injury

vascular: ischaemia neuromyopathy

Question 25

What are the most common chronic focal neuromuscular diseases?

Answer 25

degenerative: degenerative lumbosacral stenosis neoplasia: peripheral nerve sheath tumour, lumphoma inflammatory: masticatory/extraocular myositis, brachial plexus neuritis idiopathic/paraneoplastic: myasthenia gravis (focal) other: fibrotic myopathy

Question 26

What diagnostic test help define the lesion in all neuromuscular cases?

Answer 26

haematology serum biochemistry urinalysis

Question 27

What diagnostic tests help rule out endocrine and systemic dz?

Answer 27

endo: ACTH stimulation, T4/TSH systemic: thoracic/abdominal imaging

Question 28

What are the general principles of treating neuromuscular disease?

Answer 28

recumbent patients: supportive care and bladder management severe weakness can lead to resp muscle weakness = ventilatory support risk of aspiration pneumonia: monitor/tx prompltly physioo/hydrotherapy ESSENTIAL to maintain muscle mass, muscle atrophy is MAJOR concern