neuromuscular Dz Flashcards
What potential stages of the neuromuscular system may be affecte?
- neuropathy
- junctionopathy
- myopathy
> many different diseases give very similary presentations
Cardinal signs of neurouscular dz
> weakness (generalised or focal) and excercise intolerance > change in morphology - muscle atrophy (generalised or focal) - muscle hypertrophy (generalised or focal) - limb/skeletal deformities - gait abnormalities annd/or lameness (palmigrade/plantigrade stance esp neuropathies) > change in function - dysphagia (weak gag?) - regurgitation - megaoesophagus - laryngeal paralysis - dyspnoea - dysphonia (esp. neuropathies) - myalgia - weak palpebral
How does the proportion of striated muscle differ between species?
100% dog and human
80% cat
65% horse
30% pig
How may weakness manifest?
- tremors
- plantigrade/palmigrade stance
- limbs under centre of gravity, very straight
- knuckling
Defining the system.. Ddx of weakness?
> CV/resp? - hypotension - arrhythmias - hypoxaemia > metabolic/systemic - hypoglycaemia - anaemia - sepsis > paraneoplastic - thymoma -> myasthenia gravis > neuro
How can cv/resp casues be ruled out?
- hx
- PE (auscultation, pulse rate/quality)
- |Blood pressure
- ECG
- thoracic rads
- echo
How can metabolic/systemic causes be ruled out?
- hx
- PE
- haematology
- serum biochem
- electrolyte analysis
- blood gas analysis
Which electrolytes may be imbalanced -> weakness?
- hypokalamia (low head carriage and stiff limbs characteristic)
- hypocalcaemia (tremors)
- hypERmagnesaemia
How can neuro causes be refined?
> 1* neuro dz - neuromuscular > dysfunction 2* to - CV/resp - metabolic/systemic = investigations (Hx, PE, Neuro exam)
How may neuromuscular dz present other than weakness/loss of function/change in morphology?
- self mutilation if sensory only affected (some dz)
How can localision within the neuromuscular region be defined?
VERY DIFFICULT!!! - broad generalisations…
> neuropathy
- v/absent spinal reflexes and postural reactions
- platigrade/palmigrade stance
- reduced/absent muscle tone
+- neurogenic atrophy
> junctionopathy
- normal/reduced spinal reflexes and postural reactions
+- exercise intolerance
> myopathy
- spinal reflexes and postural reactions normal
- generalised weakness
- +- myalgia
Generalised neuromuscular disease indicates what localisation..
Either multiple focal lesions SC (C6-T2 and L4-S3) - RARE!
or generalised neuromuscular (most ilekly)
Something about bear skin with 4 limbs generalised. focal neuromuscular UMN/LMN?? EMAIL!!
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How can the lesion be localised neuron/NMJ/muscle?
> muscle enzymes - CK - AST - ALT > urinalysis - myoglobinuria = all these would suggest myopathy
What are EMGs?
- electromyography
- needle inserted into muscle belly, measures difference between mid and outside needle
- small waveform seen on insertion of needle
- then should be very little activity
> will not determine aetiology but will be abnormal (see waveforms) if disease affects muscle or LMN - can help differentiate disuse and denervation atrophy
- map distribution of lesions
What are the 2 main types of electrodiagnostics?
> nerve conduction studies
- measure velocity of impulse through neuron (may indicate myelination defect)
- measure time taken for conduction through wole neuro/NMJ/muscle (by subtracting time between waveforms to pass 2 needles)
- assess axon function (amplitude of wave)
EMG electromyography (mentioned prev)
How are diagnostic tests chosen?
prioritise based on Ddx (6 finger rule)
- localisation
- signalment
- onset
- progression
- symmetry
- pain
Which are the most important attributes of the disease process to limit Ddx with neuromuscular dz?
- onset and localisation > acute generalised > acute focal > chronic generalised > chronic focal
Look up all highlighted ddx as suggested further reading
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Most common cause of acute focal NMD?
trauma
Most common cause of chronic generalised NMD?
breed related
3 pathologies that serology can be carried out for?
> myasthenia gravis - nicotinic acetylcholine R Ab titre > masticatory myositis - 2M myofibre Ab titre > infectious agents - toxoplasma [cats], neospora [dogs]
What is extraocular/masticatory myositis and how can it be diagnosed?
- consistent clinical signs and imagine, NOT Dx on imaging alone
- immune mediated attack of the “M myofibres (masticatory) not sure about extraocular
What further diagnostic tests can be used to define the lesion?
- muscle biopsy
- CSF analysis (can SOMETIMEs change wih nerve root disease) usually shows central disease
- nerve biopsy
If generalised decreased reflexes seen, How can neuro and muscle athologies be differenttied?
CK to r/o muscle
- if reflexes lacking most likely neuro
How are purebred animals workedup slightly differently?
- look for predisposiions if small genetic pool!
eg. of a breed speicifc predispose disease?
> Bengal polyneuropathy
- recurrent relapsing/remitting de-re-myelination
- non-painul
- resolves spontaneously
Most common cause of polyneuropathy in cats?
- diabetic polyneuropathy
How do reflexes of cats compare to dogs?
More brisk
What type of tumour do peripheral nerve sheath tumours behave like?
Soft tissue sarcoma
