Collapse, weakness and exercise intolerance

• Collapsed cats are almost always heart disease
• When talking to the owner about history, ask about…

  • Number of events
  • Age at onset
  • Duration
  • Time of day
  • If there is any association with
  • Exercise/excitement
  • Feeding (portal systemic shunts will have their event near feeding while hypoglycaemia will be a while after eating)
  • Rest/waking
  • If they are specific and predictable in behaviour?
  • Is their behaviour normal between episodes –e.g. exercise tolerance
  • Medication –any response/cause of the episode
  • Toxin/drug access
• Prodrome/post ictal behaviour usually occurs even if only a partial seizure

  • Tonic/clonic or flaccid (syncope animals floppy then get up. Seizure –stiff limbs)
  • Autonomic signs (defecate or urinate, can happen with seizures and syncope)
  • Consciousness lost? (if so has to be due to a loss of oxygen/energy to the brain)
• History and PE can categories the collapsing problem into three groups…

  1. Seizures, fits, epilepsy and convulsions
  2. Weakness, lethargy, fatigue, reduced exercise intolerance and listlessness
  3. Syncope, fainting and collapse

  What is done next is determined by…

  • Findings on physical examination
  • Pursue clinical abnormalities and potentially any breed-specific abnormalities E.g. DCM in Dobermans
  • Severity and/or frequency of episodes
  • If exam NAD and only one episode, then do nothing as it could be a one-off
  • Financial constraints - benign neglect
• syncope = A sudden, short-lived loss of consciousness
• Syncope is a temporary failure of delivery of energy substrate to the CNS (oxygen and glucose in the blood) and is typically a failure of perfusion, likely due to a fall in BP which causes a drop in cerebral perfusion.

  • Circulation needs to be prevented for about 6 seconds + (active dogs need a longer stop than lazy dogs)
• Syncope usually has a sudden onset and consists of generalised weakness/ataxia, with a motionless flaccid collapse and a loss of consciousness. Sometimes there can be autonomic signs and/or generalised muscular activity (muscle tremor but no prodrone/post ictal phase).
• Differentials for the cause of syncope include…

  • Inappropriate vascular reflexes (these cases may present clinically normal)
  • Vasovagal reflexes
  • Carotid sinus reflexes e.g. tight collar causing a BP decrease
  • Situational e.g. tussive (coughs then syncope occurs)
  • BP falls / perfusion fails
  • Cardiac (syncope is likely to be exertional due to perfusion failure)
  • Dysrhythmia
  • Flow obstruction e.g. aortic stenosis
  • Pump failure e.g. DCM
  • Tamponade/preload failure (pericardial effusion)
  • Non-cardiac (these may present with a clinical abnormality) e.g., Metabolic or central neurological
• in this case the P wave becomes inverted indicating sino-atrial disease

  
• episodic weakness presents as intermittent/persistent exercise intolerance. The causes can be split into these groups...

  • Muscular
  • True muscular disease is rare but to diagnose perform EMG and muscle biopsies
  • Neuromuscular
  • To diagnose perform an edrophonium response test / anti Ach antibodies for myasthenia gravis
  • Orthopaedic
  • Respiratory
  • Cardiac
  • Metabolic
  • Perform a biochemistry and cortisol test to identify if there is a metabolic cause
• Most cases of episodic weakness are often orthopaedic/joint disease cases rather than muscular (OA).

  • Those with their hindlimbs being affected will be ok downstairs but bad upstairs
• The causes for seizures can be split into three groups…

  • Extracranial disease (Metabolic, toxic)
  • Metabolic diseases that can cause seizures includes hypoglycaemia, hepatic disease, severe uraemia and hypocalcaemia
  • Structural intracranial disease (space occupying lesion, haemorrhage)
  • For diagnosis perform a CSF analysis, skull radiography, CT or MRI(MRI is most useful)
  • Functional intracranial disease (Epilepsy)
  • EEG
• Hyperthermia affects any breeds/ages and occurs with exercise intolerance with variable severity. It is worse on hot days and these will pant excessively, lay down (often in wet areas) and have a rectal temperature about 41.5C. They seek water/wet grass/shade and have high blood lactate. Should consider in cases of exercise intolerance. Need to go out with the client to exercise the dog, taking a temperature before the exercise and after the event
•  

  If collapsing is an infrequent and/or benign problem…

  • Reassure the owner that this is good news
  • Monitor for future episodes and train the owner to…
  • Measure heart rate
  • Assess mucous membranes
  • Video the event if possible
  • Try and induce the event (as they are typically exercise-related problem)
  • Take a blood sample before and after
  • ECG before and after (during)
  • Take temperature (exercise induced hyperthermia can occur)
• Dogs that have multiple episodes seemed to fall into 4 groups:

  1. Syncope
  2. Collapse, no consciousness loss ONLY with exercise/excitement
  3. Collapse, no consciousness loss NOT only with exercise/excitement
  4. TENOD (tires easily, no obvious diagnosis)