Neuromuscular disease - small animal Flashcards
What are the 3 main types of neuromuscular system disorder?
- neuropathy
- junctionopathy
- myopathy
(i. e. neuromuscular = peripheral nervous system and mm) - -> many different diseases with very similar presentations
What are 2 cardinal signs of neuromuscular disease?
- weakness (generalised or focal)
- exercise intolerance
When should you suspect a neuromuscular disease?
- CARDINAL SIGNS OF NEUROMUSCULAR DISEASE: weakness (general/focal), exercise intolerance
- CHANGE IN MORPHOLOGY: mm atrophy (general/ focal), mm hypertrophy (general or focal), limb/ skeletal deformities, gait abnormalities and/or lameness
- CHANGE IN FUNCTION: dysphagia, regurgitation, megaoesophagus, laryngeal paralysis, dyspnoea, dysphonia, myalgia
- increase your suspicion the more CS there are
Define myalgia
mm pain
How do weak animals sit?
with all limbs under their centre of gravity
What might a generalised weakness caused by a polyneuropathy present as?
generalised tremor
System ddx for neuromuscular weakness - 3
- neurological
- cardiovascular/respiratory
- metabolic/systemic
Cardio/resp causes of weakness
- hypotension
- arrhythmias
- hypoxaemia etc
- TESTS: hx, PE (auscultation, pulse rate/quality), BP, ECG, thoracic radiography, echo.
Metabolic/ systemic causes of weakness
- hypoglycaemia
- anaemia
- sepsis
INVESTIGATE: hx, PE, haem, serum biochem, electrolytes, blood gas
Which electrolyte disturbances are important in causing weakness?
- HYPOKALEMIA
- hypocalcaemia (more common in LA than SA)
- hypermagnesaemia
T/F: low head carriage is a typical sign of neuromuscular weakness
True
Outline neurological causes of weakness
- PRIMARY NEUROLOGICAL DISEASE: neuromuscular
- DYSFUNCTION SECONDARY TO: cardiovascular/ respiratory, metabolic/ systemic
- INVESTIGATIONS: hx, PE, neuro exam –> normal or abnormal?
CS indicating neuro cause of weakness
- weak palpebral or gag
- dysphonia
- plantigrade/ palmigrade (latter especially) stance
- self-mutilation (sensory)
- regurgitation/ megaoesophagus
List some generalisation to distinguish neuropathy, junctionopathy and myopathy
- NEUROPATHY: reduced/absent spinal reflexes and postural reactions platigrade/palmigrade stance, reduce/ absent mm tone, +/- (neurogenic) atrophy
- JUNCTIONOPATHY: normal/reduced spinal reflexes and postural reactions, +/- exercise intolerance
- MYOPATHY: spinal reflexes and postural reactions generally normal, often generalised weakness, +/- myalgia
How can you define the location of weakness?
- MM ENZYMES: highly incresed CK, quite increase AST, increased ALT
- UA: myoglobinuria
What is EMG?
= electromyography
- a functional test
- will not determine aetiolgoy
- needle/electrode inserted into mm, measures charge b/w inside and outside of needle. Charge should be relatively quiescent with needle in.
- abnormal if disease affects: mm or LMN
- USE: distinguish disuse and denervation atrophy and mapping distribution of lesion
What is a nerve conduction study?
- to determine if nerve is abnormal or not
- METHOD: you stimulate nn along its course to mm then record mm contraction
- Amplitude determined by axons (increase –> increase)
- Velocity determined by +/- myelin
- lesions generally either affect either amplitude or veloctity
- doesn’t allow a final diagnosis
What are ddx based on?
LSO PSP:
- Localisation
- Signalment
- Onset
- Progression
- Symmetry
- Pain
- MOST USEFUL = localisation, onset, symmetry
What are the 4 main categories of ddx for neuromuscular pain?
- acute generalised
- acute focal
- chronic generalised
- chronic focal
- select are prioritise diagnostic tests based on this categorisation*
Ddx - acute generalised neuromuscular problem
- NEUROPATHY: inflammatory - polyradiculoneuritis
- JUNCTIONOPATHY - MG (fulminant), botulism, tick paralysis, (black widow, pesticices, drugs), hypocalcaemia
- MYOPATHY - hypokalaemia, (hyperkalaemic periodic paralysis, hypoadrenocorticism), exertional rhabdomyolysis
Ddx - chronic generalised neuromuscular problem
Huge ddx, most common are listed
- NEUONOPATHY: inherited and acquired MND
- NEUROPATHY: inherited polyneuropathy, diabetic polyneuropathy, chronic inflammatory demyelinating polyneuropathy, potozoal polyradiculoneuritis (Neospora)
- JUNCTIONOPATHY: MG
- MYOPATHY: hypokalaemia, immune-mediated polymyositis, paraneoplastic polymyositis, centronuclear myopathy, inherited myopathy, fibrotic myopathy (gracilis, semitendinosus myopathy), muscular dystrophy
Ddx - acute focal neuromuscular problem
- NEUROPATHY: trigeminal neuropathy, facial neuropathy, brachial plexus avulsion, femoral nn injury, sciatic nn injury, caudal nn (tail pull) injury, ischaemic neuromyoneuropathy
- JUNCTIONOPATHY: MG (focal)
- MYOPATHY: masticatory myositis, extraocular myositis, direct trauma, recumbency/ compartment syndrome, ischaemic neuromyopathy
Ddx - chronic focal neuromuscular problem
- NEUROPATHY: DLSS, peripheral nerve sheath tumour, lymphoma, meningioma,
- JUNCTIONOPATHY: MG (focal)
- MYOPATHY: masticatory myositis, extraocular myositis, fibrotic myopathy (gracilis/ semitendinosus myopathy)
Diagnostic tests to define the lesion
- Haematology
- biochem
- ACTH stim?
- T4?
- Serology:
- MG (nicotinic Ach -R Ab titre)
- Masticatory myositis (2M myofibre Ab titre)
- Infectious agents (toxoplasma, neospora)
- Genetic testing (interpret based on CS)
- Metabolic screening (urine)
- CSF sample
- mm biopsy
- nn biopsy
Best imaging modality for spinal cord?
= MRI
- best for peripheral nn
- good tissue contrast
(CT - good for enlarged brachial plexus)
T/F: disease of nn roots may cause changes in CSF
True
2 sites for CSF samples
- cisternal
- lumbar
Localisation: decreased mm tone, decreased reflexes, both in all 4 limbs
= LMN signs so therefore generalised neuromuscular (most likely) or 2 lesions in spinal cord (C6-T2 and L4-S3; rare)
How do you determine is a lesion is in brainstem or peripheral?
- Brainstem lesion: affects mentation, postural reactions, CN deficits
- Even if several CN deficits but mentation, gait and postural reactions are normal, suggests a peripheral lesion most likely
Cause - trigeminal neuropathy
- usually idiopathic, possibly neuritis
Tx - trigeminal neuropathy
Self-resolving in several weeks so tx usually supportive; wet food, symptomatic management
Which nn does the gastrocnemius reflex test?
femoral and sciatic (n.b. withdrawal is better indicator of sciatic nn problem)
Tx - malignant peripheral nn sheath tumour
- this behaves like STS
- tx for both is sx excision (aggressive)
- always consider location, if poor location - consider euthanasia
