Encephalopathies

Question 1

what is the ascending reticular activating system in the brainstem? purpose?
- what is mental status governed by, and when can it get messed up?

Answer 1

• ARAS channels sensory input from body to activate cortex
• Measures response to environment
• Mentation: awareness vs arousal
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• Mental status is a function of two major areas in the brain: the brainstem and thalamo-cortex
• Normal mentation: any time sensory input comes in, it is transmitted through ARAS (reticular formation, in the brainstem) and then the response to environmental stimuli is coordinated
  o Abnormal mentation results with an abnormality in the brainstem or thalamo-cortex

Question 2

Mentation: Responsiveness
- what are awareness vs arousal

Answer 2

awareness:
- bright, alert, responsive
- disoriented / dissociated
- demented / delirious
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Arousal:
- BAR
- depressed / obtunded
- stuporous
- comatose

Question 3

Depressed/obtunded vs stuporous vs comatose?
- signs, and parts of the brain that are affected?

Answer 3

Depressed/obtunded:
- Drowsiness, inattention, less responsive to environment
- Brainstem (ARAS), Thalamocortex
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Stuporous:
- Unconsciousness + decreased responsiveness - Can be aroused with noxious stimulus
- Partial disconnection
- Brainstem (ARAS)
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Comatose:
- Unconsciousness + NO responsiveness
- Total disconnection
- Reflexes may be intact
- Brainstem (ARAS)

Question 4

disorientation can be due to abnormalities in what structures?

Answer 4

Thalamocortex &/or vestibulocerebellar

Question 5

thalamus vs cortex lesions - how to distinguish on neuro exam

Answer 5

• we cannot!

Question 6

Thalamocortex: NE, what we see if lesion

Answer 6

• Mentation: depression / delirium / disorientation / Δ behaviour
  > Head pressing, compulsion, wandering, pacing
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• Gait & Posture: circling (ipsi), body turn (ipsi torticollis or pleurothotonus)
  > Mild hemiparesis (contra)
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• Cranial Nerves: menace & nasal septum response deficits (contra)
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• Postural Reactions: Contralateral proprioceptive deficits with near-normal gait
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• Spinal reflexes: Normal
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• Palpation (Spinal Pain): possible neck pain
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• Seizures are always a sign of thalmo-cortex disease

Question 7

Clinical Signs of Brain Dysfunction – Brain Stem

Answer 7

• Mentation: Depressed/stupor/coma
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• Gait and posture:
  > Tetraparesis/plegia vs hemiparesis/plegia (UMN signs)
  > decerebrate rigidity (hyperextension of front limbs and head, poor prognosis) and/or opistothonus
  > vestibular ataxia (central)
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• Cranial nerves:
  > Deficits in cranial nerves III-XII
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• Postural reactions:
  > All four limbs ipsilateral deficits
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• Spinal reflexes: Normal
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• Palpation: Neck pain on palpation is possible

Question 8

Encephalopathy: Clinical Signs
- what anatomy may be affected?
- lesion localization?

Answer 8

• Thalamocortex ± Brainstem ± Cerebellum
• Lesion localization: diffuse vs multifocal
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  Beware the focal lesion:
• Extensive mass invading multiple CNS regions
• Focal lesion w/ extensive 2nd surrounding edema
• Focal obstruction of CSF flow > hydrocephalus

Question 9

Encephalitis - what is it? categories?

Answer 9

• Result of inflammatory/infectious conditions, which in the CNS commonly affect several areas
  > Encephalitis: brain
  > Myelitis: spinal cord
  > Meningitis: meninges
  > Various combinations possible, e.g. meningoencephalitis, meningomyelitis,etc.
• Both infectious and non-infectious causes

Question 10

issues with what structure are responsible for pain in encephalitis cases?

Answer 10

meninges is the painful part, spinal cord and brain have no pain receptors

Question 11

Infectious Encephalitis - common causes

Answer 11

• Viral: canine distemper, FIP (cats), rabies
• Rickettsial: Ehrlichia canis, RMS
• Bacterial: Staph, Strep, coliforms
• Fungal: blasto, histo, crypto, coccidioides, aspergillosis
• Protozoal: Toxoplasma, Neospora
• Parasitic: verminous, larval migrans, cysticercosis…

Question 12

Non-infectious Encephalitis
- etiology
- prevalence in dogs vs infectious
- types, what we can call it with vs without histopath dx
- tx

Answer 12

• Immune-mediated
• Dogs (Canada): more common than infectious
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  Without histopath:
• Meningoencephalitis of unknown etiology (MUE)
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  With histopath:
• Granulomatous meningoencephalomyelitis (GME) vs Necrotizing encephalitis (NE)
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  Treatment:
• Immunosuppression > Steroids ± others

Question 13

Granulomatous meningoencephalomyelitis (GME)
- what anatomy is affected? distribution?
- what animals are affected?
- prognosis?

Answer 13

• Brain, spinal cord, meninges
• Focal vs multifocal vs ocular (CN II)
• Mostly dogs (cats tend not to have this issue) > Any age, breed: tendency to small & 3-5y
• Prognosis: guarded to poor

Question 14

Necrotizing Encephalitis
- who gets this?
- signs?
- prognosis?
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- categories based on affected anatomy, and who is affected?

Answer 14

• Small breeds, younger age (2-5y)
• Seizures
• Prognosis: poor to grave
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• Necrotizing Meningoencephalitis (NME)
  > Cerebral grey + white matter, meninges
  > Pug, Maltese, Chihuahua, etc.
  “pugs are the ememy (NME)”
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• Necrotizing Leukoencephalitis (NLE)
  > Brainstem, cerebral white matter
  > Yorkshire Terrier & French Bulldog

Question 15

Encephalitis: Diagnostic Tests

Answer 15

• CBC / chem / UA, Thoracic rads, abdominal ultrasound
  > Non-infectious: NAF
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• MRI: best, very sensitive to soft tissue changes, can see any inflammation/edema due to encephalitis
• CSF analysis: increased inflammatory cell count and protein levels, but non-specific
• Titres, PCRs based on suspected infectious disease
• Histopathology gives a definitive diagnosis

Question 16

Brain Tumours
- who gets them?
- what types are there and which is more common?

Answer 16

• Older dogs & cats
• Primary > > secondary
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• Primary:
  > neurons, glial cells, choroid plexus, ependymal, meninges
• secondary:
  > local extension or be metastatic

Question 17

Primary Brain Tumours - what types are there? what is most common?

Answer 17

• Meningioma: most common
• Glioma (brachycephalics get more of these) > Astrocytoma, oligodendroglioma, glioblastoma
• Choroid Plexus Tumour > Papilloma vs carcinoma
• Ependymoma

Question 18

Secondary Brain Tumours
- which types are prone to local extension? metastatic?

Answer 18

Local extension:
- Calvarial (osteosarcoma, MLO)
- Nasal carcinoma
- Pituitary tumour
- NST (CN V)
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Metastatic:
- HSA
- LSA
- Carcinoma – mammary, pulmonary, prostatic
- Malignant melanoma

Question 19

Brain Tumours: Tx

Answer 19

• Factors: tumour type, location, morbidity/mortality, cost
• Corticosteroids
• Chemotherapy: lomustine, hydroxyurea, cytosine arabinoside
• Radiation therapy: linear accelerator, gamma knife
• Surgery

Question 20

Metabolic Encephalopathies
- which neurons most susceptible? why?
- types?

Answer 20

• Cerebrocortical neurons most susceptible to
  metabolic disruption (high energy demands, little reserve)
• Hepatic encephalopathy: Congenital PSS, microvascular dysplasia, acute hepatotoxicity
• Renal encephalopathy (aka uremic encephalopathy)
• Others:
  > Hypoglycemia
  > Electrolyte imbalances (e.g. sodium)
  > Hypoperfusion

Question 21

Metabolic Encephalopathies
Clinical Signs:

Answer 21

• Symmetrical (whole system affected)
• Thalamocortical
  > Depression, disorientation
  > Pacing, head pressing
  > Menace response deficits
  > Seizures

Question 22

Congenital Disorders of the brain

Answer 22

• hydrocephalus most common
• Arachnoid diverticuli, lissencephaly, etc.