Clinical Reasoning in Neurology Flashcards
Making a good differential list.
Needs to be:
- long enough to have both the common and rare causes on it.
- short enough to use.
- logical enough to generate quickly.
Use aetiological categories to achieve these.
DAMNIT TV.
Degenerative.
- e.g. cell death e.g. cognitive dysfunction, compression e.g. disc protrusion etc.
Anomalous.
- developmental e.g. cerebellar hypoplasia.
Metabolic.
- excess/deficiency e.g. hepatic encephalopathy, thiamine deficiency.
Neoplastic.
- mass of unregulated cell division e.g. lymphoma.
Inflammatory.
- immune-mediated vs infectious, then bacterial vs viral vs protozoal.
e.g. toxoplasma, immune-mediated encephalitis.
Toxic.
- excess of exogenous substances e.g. metaldehyde toxicity.
Traumatic.
- damage to NS from compression, contusion, laceration by external sources e.g. disc extrusion, fracture, luxation.
Vascular.
- interruption in blood supply or excess of blood e.g. infarction, haematoma.
The five finger rule - prioritising clinical info.
Thumb - signalment.
– Dachs - discs, GSD - degenerative myelopathy, pugs - arachnoid cysts, hemivertebrae, disc extrusion.
Index - onset.
– toxins = short, inflammatory = relatively short, degenerative and anomalous = long.
Middle - progression.
– whether getting worse or better.
Ring - symmetry.
– unilateral or bilateral.
–> unilateral indicative of neoplasia, granulomas, vascular etc.
–> other symmetrical diseases may include toxins or nutritional deficiencies e.g. thiamine deficiency always bilaterally symmetrical.
Pinky - pain.
Aids localisation and so differential diagnoses.
Onset and progression terminology.
Onset (or how long it took to go from normal to their worst?)
- peracute = seconds to minutes.
- acute = minutes to hours.
- subacute = 24-48hrs.
- insidious = over 48hrs.
Progression (or whether the most severe signs have already been reached).
Disease types that get better by themselves.
Toxic, traumatic, vascular.
*non-progressive.
Nociception and the CNS.
No nociceptors in the spinal cord.
- so CNS structures do not generate pain.
BUT these structures are surrounded by other structures that do contain nociceptors:
- meninges, periosteum (and disc).
- muscle, CT etc.
- nerve roots do not have nociceptors where they exit the vertebral canal BUT do discharge if compressed or inflamed and send input to pain-sensing areas of the brain even though the receptors are not stimulated.
- non-painful = degenerative, anomalous (sometimes), metabolic, toxic, vascular.
- painful = anomalous (sometimes), neoplastic, inflammatory, traumatic.
Localisation step uses.
Used to order the aetiological categories by degree of likelihood.
Use to integrate w/ the aetiological categories and provide specific differential diagnoses.
Localisation terminology…
1. Focal.
2. Multifocal.
3. Diffuse.
4. Multisystemic.
- One discrete area.
- 2 or more discrete areas.
- 2 or more adjacent areas.
- More than one body system.
Top 3 diseases by localisation…
1. brain.
2. cranial nerve.
3. spinal cord.
4. spinal nerve.
- meningioma/glioma.
Auto-immune encephalitis.
Idiopathic epilepsy. - Idiopathic neuropathy.
Nerve tumour.
Inflammation of adjacent structures e.g. otitis media/interna. - DISC DISEASE.
Compression from vertebral structures.
Infarction.
(Fibrocartilaginous embolism). - Nerve tumour.
Trauma e.g. brachial plexus avulsion.
Central vs peripheral cranial neuropathy (i.e. nerve vs brainstem).
Likely central dz if:
- obtunded – reticular activating system affected.
- paretic – ascending and descending motor tracts are affected.
Suspect peripheral dz if:
- ALL signs can be explained by only one nerve not working.
Multiple nerves affected can indicate central dz (if obtunded or paretic) or peripheral dz (esp. if they all exit in same location e.g. facial (VII) and vestibular (VIII) in middle ear.
Assessing spinal cord injury severity.
Proprioceptive fibres are most peripheral in spinal cord.
Motor fibres are next most peripheral in spinal cord.
Nociceptive fibres are most central in spinal cord.
So…
Proprioceptive ataxia gives good px and usually reversible.
Ataxia and paresis/plegia gives fair px and most recover.
Plegia and lack of pain perception gives a guarded px.
What indicates pain perception.
A behavioural response e.g. turning head, licking lips, indicates pain perception.
Withdrawing leg is a reflex and can occur even if spinal cord is severed.
Because pain fibres are deep in the cord, animals w/ no reaction are sometimes called ‘deep pain negative’.
Assessing brain injury severity.
Signs often reflect localisation, not severity.
- need structured assessment to ensure correct areas tested.
Assessment needs to be systematic to monitor progression, and simple to ensure repeatability.
Use modified Glasgow coma score (MGCS).
Modified Glasgow Coma Score.
Assesses forebrain, cerebellum, brainstem.
- by valuating movement, reflexes and consciousness.
Can be used to monitor overtime.
Is consistent.
Quick and effective.
Has px info:
- 15-18 = good.
- 9-14 = guarded.
- 3-8 = grave.
Scoring on:
- motor activity.
- brainstem reflexes.
- level of consciousness.
Measuring injury severity - Cushing’s reflex.
ICP increases:
- local brain perfusion reduced.
- sympathetic response to increase blood flow (increase HR and BP).
So hypertension:
- increased BP sensed by peripheral baroreceptors.
- reflex slowing of HR.
So bradycardia:
- pathognomonic hypertension and bradycardia.
*Only seen in unconscious animals.
*Helpful in identifying end-of-life.
