Neurology Flashcards
How many dogs with portosystemic shunts display neurologic signs?
95%
Name 4 neurologic signs of hepatic encephalopathy
Decreased ability to learn, behavioral changes, head pressing, seizures, blindness
Are neurologic signs more common when shunts insert cranial to or caudal to the liver
Caudal
Name 3 endotoxins thought to be involved in the development of hepatic encephalopathy
Ammonia, amino acids (tryptophan), GABA, mercaptans
Hyperammonemia has been documented in young Irish Wolfhounds due to what deficiency?
Deficiency in urea cycle enzymes
What neurologic signs can be seen in hypothyroid dogs?
Acute or chronic, progressive central vestibular signs
Name 4 clinical signs of myxedema coma in dogs
Mentation changes due to brain edema, hypothermia without shivering, non-pitting skin edema, bradycardia
Name 3 mild CNS signs noted in cats with hyperthyroidism
Hyperactivity, changes in sleep/wake cycles, aggression, obtundation
How large are pituitary tumors before they result in neurologic signs?
Typically >1 to 1.5cm diameter
Pituitary tumors result in neurologic signs in what percent of dogs before or after diagnosis of hyperadrenocorticism?
15-30%
Name 4 neurologic signs of a pituitary macroadenoma
Obtundation, pacing, circling, disorientation, ataxia, seizures
How does persistent hypoglycemia results in neurologic damage?
Leads to vasoconstriction and hypoxia
Name two tumors capable of resulting in hypoglycemia
Insulinoma, leiomyosarcoma
What drug can be used to treat insulin producing tumors because it inhibits insulin secretion, stimulates production of glucose by the liver, and inhibits uptake of glucose by cells?
Diazoxide
What role does thiamine play in the body?
Essential cofactor for carbohydrate metabolism - essential for utilization of pyruvic acid in the TCA cycle and pentose phosphate pathway. Absence of thiamine leads to excessive lactic acid buildup as anaerobic metabolism occurs
How can thiamine deficiency result in dogs and cats?
Fed meats preserved with sulfur dioxide, thiaminase-containing raw fish
What are the histopathologic findings associated with thiamine deficiency?
Polioencephalomalacia
Name 3 clinical signs of thiamine deficiency
Vestibular signs, spastic cervical ventroflexion in cats, vision loss, mydriasis without pupil light reflexes, incoordination, ataxia, and seizures
How does hypocalcemia alter membrane excitability?
Increases it
Name 3 neurologic signs of hypocalcemia
Facial rubbing, stiffness, muscle twitching, nervousness, tetany, and seizures
Severe hyponatremia results in what changes to the brain?
Cerebral edema, diffuse encephalopathy
Rapid correction of hyponatremia can result in what histopathologic changes in the brain? How long after correction do these signs manifest?
Central pontine myelinolysis; occurs 48 hours to days after correction
When correcting hyponatremia, the serum sodium concentration should not rise by more than ____ in 24 hours?
10 mEq/L
Acute hypernatremia can cause what changes to the brain?
Decrease in brain volume from osmotic shifts, leading to vascular rupture and focal hemorrhage
In chronic hypernatremia, the brain adjusts to hypertonicity by producing what substance?
Idiogenic osmoles
Rapid correction of hypernatremia results in what changes to the brain?
Cerebral edema
T4 stimulates mitochondrial respiratory activity, thereby leading to ATP production. In hypothyroidism, how does ATP deficiency affect peripheral nerves?
Impairs the function of the Na/K pump, leading to decreased axonal transport ==> leads to axonal degeneration and demyelination
List 3 neurologic signs of hypothyroidism
Weakness, muscle atrophy, laryngeal paralysis, megaesophagus facial paralysis, peripheral vestibular signs
What hormonal disease causes fibrotic myopathy and polyneuropathy?
Hyperadrenocorticism
Name 3 clinical signs of fibrotic myopathy
Stiff, stilted gain, difficulty flexing the limbs, generalized muscle atrophy
Name 3 signs of diabetic polyneuropathy in cats
Plantigrade stance, difficulty jumping, CP deficits, decreased tendon reflexes, muscle atrophy
Name two feline diseases that may result in hypokalemia
CKD, hyperaldosteronism
What is the reticular activating system and what is it responsible for?
Network of nuclei in the brainstem. Activate the cerebral cortex to maintain consciousness
What is the function of the cerebrum?
Integrates sensory info, plans motor activity, responsible for emotion and memory
Diffuse, bilateral forebrain lesions will result in stupor/coma. How will they affect movement and reflexes?
Tetraparesis, postural deficits are present. Reflexes are normal but vision is absent
Lesions of the rostral brainstem will result in stupor/coma. How will they affect movement and reflexes?
Bilateral lesions will cause tetraparesis, unilateral lesions will cause hemiparesis. Postural deficits present. Reflexes are exaggerated with increased extensor tone
Name 3 brainstem reflexes
Pupil size/symmetry and response to light. Physiologic nystagmus. Dazzle reflex. Palpebral reflex
If a patient has unilateral mydriasis with no pupillary response to light, where is the lesion located?
Cranial nerve III
If a patient has unilateral mydriasis AND ventrolateral strabismus with no response to light, where is the lesion located?
Midbrain
Describe Cheyne-Stokes breathing
Alternating hypernea and apnea
Describe apneusis. Where is the lesion located
Breathing raises for a full inspiratory period with otherwise normal breathing. Pontine lesions
What equation describes cranial perfusion pressure (CPP)
CPP = MAP - ICP
Describe the Cushing’s reflex
If ICP rises, the MAP increases to maintain CPP. Systemic hypertension triggers the baroflex, leading to bradycardia
Name 3 causes of hepatic encephalopathy
A = acute, fulminant liver disease
B = bypass (portosystemic shunts)
C = cirrhosis (cirrhotic liver, portal hypertension, acquired shunting)
Acute, fulminant liver disease can result in hepatic encephalopathy by what pathologic change?
Cytotoxic brain edema. Can lead to intracranial hypertension and brain herniation
What causes cytotoxic brain edema?
Failure of ion pumps, so no sodium efflux occurs. Water shifts to the intracellular space to maintain iso-osmotic state => edema. BBB is intact
What causes vasogenic edema?
Disruption of the BBB, which triggers a cascade of inflammatory and vasoactive mediators. Often causes by tumors
Chronic hepatic disease can result in hepatic encephalopathy by what pathologic change?
Alzheimer type II astrocytosis - astrocytes change structure and function. Very minimal brain edema
Name 2 non-hepatic causes of hyperammonemia
Vitamin B12 deficiency. Arginine deficiency in cats
Name 3 sources of ammonia in the body
Bacteria breakdown of proteins, urease bacterial breakdown of urea, intestinal breakdown of glutamine
Which form of ammonia is absorbed from the gut (NH3 or NH4+)?
NH3
In the periportal hepatocytes, ammonia is converted into _____ via the _____ pathway
Urea, urea cycle
How does arginine deficiency in cats lead to hyperammonemia?
Arginine is an important component of the urea cycle. Without it, ammonia cannot be converted into urea. Essential amino acid in cats
How does ammonia affect glutamate in the brain?
Ammonia is added to glutamate (a major neurotransmitter) to form glutamine. Glutamine is taken up by astrocytes and is osmotically active, leading to edema formation
What hepatic synthetic parameter is NOT affected by PSS?
Bilirubin (hyperbilirubinemia is not a feature of congenital PSS)
What is the major excitatory neurotransmitter?
Glutamate
What is the major inhibitory neurotransmitter?
GABA
Name two catecholamine based neurotransmitters
Dopamine, norepinephrine
What type of amino acids are precursors to catecholamines?
Aromatic amino acids: phenylalanine, tyrosine, tryptophan
Aromatic amino acids are usually removed by the liver. How do they contribute to hepatic encephalopathy
Can build up and become false neurotransmitters
What amino acids may be decreased with liver failure?
Branched chain amino acids: leucine, valine, isoleucine
How does lactulose reduce hyperammonemia?
Broken down into acid byproducts in the gut. The acidity traps NH3 in the NH4 form, which is not absorbed
How do antibiotics reduce hyperammonemia?
Reduce the number of urease producing bacteria
What is dialysis disequilibrium syndrome?
A rapid decline in peripheral osmolality results from dialysis => cerebral edema => increased ICP
What is kernicterus?
Deposition of bilirubin in the grey matter and spinal cord => neuronal degeneration
