Presenting Signs: Episodic Collapse

Question 1

1. Collapse.
2. Syncope.
3. Pre-syncope.

Answer 1

1. sudden loss of postural tone.
   - sustained collapse also possible.
2. Fainting, collapse w/ transient loss of consciousness.
3. PARTIAL loss of consciousness - often associated w/ stumbling/ataxia.

Question 2

Syncope vs seizures.

Answer 2

• Syncope at wake or at exercise, seizure when at rest.
• Syncope preceded by pre-syncopal event/ataxia.
• Seizures involve loss of consciousness and unresponsiveness to environment.
• Syncope typically flaccid collapse, seizures usually stiffening, tonic clonic movements, jaw chomp/chatter/salivation.
• Syncope w/ no autonomic signs, seizures +/- autonomic signs e.g. urination, defaecation.
• Syncope = seconds to mins, seizures <2-5mins.
• Syncope has rapid recovery, seizures have longer recovery.

Question 3

3 main divisions for intermittent collapse differentials.

Answer 3

Cardiorespiratory - blood and O2 to brain to maintain control over postural responses.
Metabolic e.g. hypoglycaemia.
Neuromuscular - e.g. arthritis.

Question 4

Most common cause of failure of oxygen delivery to the cells, resulting on syncope.

Answer 4

Cardiac arrhythmias.

Question 5

Cardiac causes of syncope.

Answer 5

Intermittent, marked hypotension caused by:
- arrhythmias:
– tachyarrhythmias –> impede filling / impaired output.
– bradyarrhythmias –> impaired output.
- neurocardiogenic reflexes.
- much less commonly:
– myocardial/valvular disease.
– R to L shunts.
– pericardial effusions.

Question 6

Vasovagal syncope.

Answer 6

Form of neurocardiogenic syncope.
Combination of:
- Bradycardia/bradyarrhythmia w/ reflex vasodilation.
Failure of autonomic function:
- abrupt increase in vagal tone.
- transient withdrawal of sympathetic tone.
Various triggering events:
- marked excitement in apparently healthy dogs e.g. young boxers.

Question 7

Other causes of neurocardiogenic syncope.

Answer 7

May be triggered by various physiologic events:
- coughing (tussive syncope), sneezing.
- swallowing, vomiting, defaecating, urinating.
- Visceral pain.

– Coughing = increased intrathoracic pressure impeding venous return?
– Vasovagal events = high vagal tone w/ respiratory disease (incl. brachycephaly) and GI disease.

Question 8

Respiratory causes of syncope.

Answer 8

Rare.
Usually present w/ obvious respiratory signs rather than syncope.
Typically intermittent URT obstruction.
- Hx.
- URT noise relevant to affected anatomy.
– stertor –> pharyngeal.
– stridor –> laryngeal.
– goose-honking –> tracheal collapse.
LRT airway / pulmonary parenchymal disease usually associated w/ coughing/tachypnoea.

Question 9

Anaemia as a cause of syncope.

Answer 9

Inadequate O2 carrying capacity for tissue (i.e. brain) oxygenation.
Most commonly causes sustained lethargy/weakness rather than syncopal events.

Question 10

Metabolic causes of intermittent collapse.

Answer 10

Hypoglycaemia.
Electrolyte derangements (required for muscle contraction/movement):
- hypokalaemia.
- hypocalcaemia.
Endocrinopathies:
- hypoadrenocorticism (Addison’s).
- hypothyroidism (usually exercise intolerant – rarely episodic collapse).

Question 11

Differentials for hypoglycaemia.

Answer 11

Inadequate synthesis:
- Hepatic dysfunction / portosystemic shunting.
- Toy dog, inadequate glycogen stores.
- Hypoadrenocorticism.
Excessive consumption - sepsis.
Excess hypoglycaemic agents:
- insulin – exogenous vs insulinoma.
- xylitol toxicity.
- oral hypoglycaemics (diabetic owner).
Paraneoplastic: insulinoma, hepatomas, IGF-2 producing tumours.

Question 12

1. Investigation of hypoglycaemia in animal w/ suspected hepatic dysfunction / portovascular anomaly.
2. Investigation of hypoglycaemia - how would you rule out Addison’s?
3. Investigation of hypoglycaemia when sepsis suspected?
4. Investigation of hypoglycaemia when neoplasm suspected?
5. Investigation of hypoglycaemia when insulinoma suspected?

Answer 12

1. Biochemistry, BAST, imaging.
2. Basal cortisol/ACTH stim.
3. T-FAST / A-FAST / other imaging (fluid).
4. Imaging, hepatoma (liver); IGF-2 producing tumours (typically smooth muscle).
5. Blood sample at point of low glucose.
   Measure insulin levels from that sample to see insulin levels at that same point in time. If insulinoma, insulin inappropriately high (top half of normal or above).

Question 13

Insulinoma.

Answer 13

Tumour of pancreatic B-cells > excessive unregulated insulin production > hypoglycaemia > neuroglycopenia:
- typically episodic.
- disorientation, ataxia, lethargy, weakness, collapse, seizures, (coma, death).
Uncommon in dogs.
Rare in cats.
Animals affected usually middle-aged to older.

Question 14

Dx insulinoma.

Answer 14

Blood sample at point of low glucose to measure insulin at that point (Oxalate fluoride tube).
Hypoglycaemia w/ inappropriate insulin levels (upper half of reference range or higher).
May be challenging to demonstrate as hypoglycaemia frequently intermittent.
Imaging shows pancreatic nodule, but may be v small / not visible on imaging. CT may be required.

Question 15

1. Management of hypoglycaemia in patient w/ life threatening signs.
2. Management of hypoglycaemia in patient w/ no-to-mild signs.

Answer 15

1. IV available: IV glucose bolus.
   No IV available: glucogel on MM and get IV access.
2. Anorexic - glucose CRI (2.5-5%) in fluids.
   If eating - feed high-fibre complex-carbohydrate diet little and often.
   Restricted/gentle exercise.

Question 16

Management of patient w/ insulinoma.

Answer 16

Surgical resection:
- Tx of choice (primary, palpable metastases) – referral.
- Mean survival time 1-2yrs – recurrence expected due to metastasis.
Chemotherapy? - high expense / toxicity.
Conservative management:
- dietary modification for hypoglycaemia.
- exercise restriction/modification.
- steroids (insulin antagonism).
- mean survival time = 2-8m.

Question 17

Neuromuscular causes of syncope.

Answer 17

Neuropathy, junctionopathy, myopathy.
Sodium, potassium, calcium; principal electrolytes required for APs / muscle contraction / maintenance of muscular tone.
Most NM diseases show sustained signs.
Myasthenia gravis.
Exercise-induced collapse (labs).
Paroxysmal movement disorders e.g. epileptoid cramping syndrome (originally recognised in border terriers, possible related to dietary gluten).

Question 18

Myasthenia gravis.

Answer 18

Ab-mediated destruction of the acetyl choline receptor.
- failure of sustained impulse conduction.
- rest and recover.
3 forms:
- systemic, episodic (exertion associated) collapse.
- systemic, fulminant, sustained collapse.
- focal; megaoesophagus/regurgitation.

Question 19

1. Myasthenia gravis testing.
2. Myasthenia gravis Tx.

Answer 19

1. Blood test for acetyl choline receptor Abs.
2. Acetyl choline esterase inhibitors to stop breakdown of acetyl choline and upregulate it.

Question 20

Investigating episodic collapse.

Answer 20

Characterise events fully:
- directly observe the pet / obtainvid from O.
Thorough CE (incl. neuro).
Chase any abnormalities e.g. arrhythmia, start w/ ECG; pallor, start w/ PCV).
Normal exam:
- signalment predispositions.
- start simply / with cheaper tests to evaluate for hypoxia or metabolic disease.
- cardiac evaluation; ECG +/- holter analysis +/- echocardiography.
- further metabolic/neuromuscular evaluation.

Question 21

Initial non-invasive, rapid Dx.

Answer 21

BG and electrolytes. - hypoglycaemia may be intermittent.
Systolic BP.
Peripheral oxygenation:
- SpO2.
- or arterial blood gas analysis.
- +/- incl. during/post-exercise.

Question 22

Other useful screening lab tests.

Answer 22

PCV.
CK activity.
Full haematology and serum biochemistry to show subtle findings to suggest conditions like Addison’s to lead onto further dx e.g. basal cortisol/ACTH stim.
Suspicious of myasthenia – chest x ray.

Question 23

Evaluating for cardiac causes of episodic collapse.

Answer 23

ECG - arrhythmias.
Holter ECG (24-48h) w/ event diary.
- encourage exercise/activity to induce episode during Holter.
- Arrhythmia w/ event > Dx.
- even w/o episode, most clinically significant arrhythmias will be captured (in part) over this time frame.
Insertable loop recorder.
Echo - for structural disease / pulmonary hypertension.
- lower yield of info than rhythm evaluation.

Question 24

Screening for neuro causes of episodic collapse.

Answer 24

Acetyl choline receptor (AChR) Abs (serum test) and Tensilon test (edrophonium response test for myasthenia gravis.

Genetic tests e.g. for exercise-induced collapse in labs.

EMG, muscle and nerve biopsy, MRI may be required.

Question 25

What if still cannot figure out cause of episodic collapse?

Answer 25

Wait for progression.
Refer.