Muscle Diseases Flashcards
Which of the following diseases on the 5 panel plus test for Quarter Horses and related breeds is related to the muscle?
a. glycogen branching enzyme deficiency
b. hereditary equine regional dermastenia
c. hyperkalemic periodic paralysis
d. myosin heavy chain mypoathy
e. malignant hyperthermia
f. polysaccharide storage myopathy
A, C, D, E, F
What is important to note about creatinine kinase in diagnosing muscle disease?
takes awhile to increase
- baseline sample
- sample taken after 15 mins of exercise
- another sample taken 4-6 hrs after
What is myotonia?
delayed relaxation or prolonged contraction of skeletal muscle following voluntary contraction or stimulation, leading to muscle fasciculations and weakness
What is hyperkalemic periodic paralysis (HYPP)? What breeds are predisposed?
autosomal dominant mutation in SCN4A gene causes an abnormality in voltage-gated skeletal muscle Na channels, leading to increased muscle excitability
Western breeds: AQH, APH, Appaloosa
What is the root cause of hyperkalemic periodic paralysis (HYPP)?
first identified in AQH stallion, Impressive —> all horses from his blood line are required to be tested and homozygotes are illegible for registration
What is the pathophysiology of hyperkalemic periodic paralysis (HYPP)?
- K intake or exercise followed by rest causes a small increase in extracellular K
- light membrane depolarization opens Na channels with failure of abnormal channels to inactivate
- persistent inward Na current increases intracellular Na, leading to sustained depolarization of cell membranes
- K efflux causes even more extracellular increase
- inactivation of normal Na channels causes loss of electrical excitability and paralysis
What are 4 general triggers to hyperkalemic periodic paralysis (HYPP)?
- diet changes or fasting
- high K food, like alfalfa and molasses
- anesthesia, heavy sedation
- stress: trailer ride, cold, pregnancy, concurrent disease
What extra sign is seen in foals with hyperkalemic periodic paralysis (HYPP)?
upper respiratory obstruction
What are the initial and progressive signs of a hyperkalemic periodic paralysis (HYPP) episode?
INITIAL - brief myotonia with prolapse of third eyelid, sweating, muscle fasciculations in the flank, neck, and shoulders
PROGRESSION - more generalize and associated with additional muscle groups and aggravated by stimuli, swaying, staggering, dog sitting, recumbency, tachycardia, tachypnea, stridor
What 2 things are most commonly seen in patients with hyperkalemic periodic paralysis (HYPP)?
- hemoconcentration
- mild hyponatremia
hyperkalemia not always present!
What are 4 causes of hyperkalemia in blood samples that can be confused with hyperkalemic periodic paralysis (HYPP)?
- delay before sample centrifugation = hemolysis
- EDTA sample
- acidosis, renal failure, severe rhabdomyolysis
- high intensity exercise
What is the most reliable way of diagnosing hyperkalemic periodic paralysis (HYPP)?
genetic testing with 20-30 mane/tail hairs with roots
What are the 3 major steps to hyperkalemic periodic paralysis (HYPP) prevention?
- decrease potassium intake (<0.6-1.1% of total ration)
- increase potassium loss
- avoid triggers
In what 3 ways can potassium intake be decreased in patients with hyperkalemic periodic paralysis (HYPP)?
- forage - let horses graze on grass with high water content, use later cuts of timothy or Bermuda grass hay
- grain - feed small meals of oats, corn, wheat, barley, and beet pulp more frequently, provide complete pelleted feed
- provide regular exercise
What parts of the diet should be avoided in patients with hyperkalemic periodic paralysis (HYPP)?
- alfalfa hay
- first cutting hay
- orchard grass
- molasses
- supplements
How is potassium loss instigated in horses with hyperkalemic periodic paralysis (HYPP)? What are 2 examples?
diuretics that increase renal potassium loss (use may be restricted during competition)
- Acetazolamide
- Hydrochlorothiazide
How can triggers of hyperkalemic periodic paralysis (HYPP) be avoided?
- minimize stress
- provide regular exercise and small meals
- avoid heavy sedation
- prepare minor sedation to reduce stress associated with travel and veterinary visits
What treatment is recommended in patients undergoing mild episodes of hyperkalemic periodic paralysis (HYPP)?
give grain and Karo syrup PO and walk the horse
What 4 treatments are recommended for patients undergoing severe episodes of hyperkalemic periodic paralysis (HYPP)?
- facilitate potassium uptake into cells - IV dextrose +/- calcium gluconate or sodium bicarbonate
- raise membrane threshold potential - calcium gluconate
- facilitate potassium loss - Acetazolamide
- tracheotomy if in severe respiratory distress
What affects the severity of signs associated with hyperkalemic periodic paralysis (HYPP)?
autosomal dominant - homozygous (NN) > heterozygous (Hh) - AQH, APH
- hh = no signs
What is glycogen branching enzyme deficiency (GBED)? What horses are affected?
autosomal recessive mutation of GBE1 gene resulting in an accumulation of unbranched glycogen in tissues and inability to store glucose in tissues
AQH homozygotes get sick and die
What are the 3 most common signs of glycogen branching enzyme deficiency (GBED)? What are some other signs?
- abortion, still birth
- intermittent seizures
- muscle weakness
hypothermia, flexural deformities, collapse, ventilatory failure, cardiac arrhythmias, sudden death
What are 3 signs on clinical pathology in horses with glycogen branching enzyme deficiency (GBED)?
- persistent leukopenia
- intermittent hypoglycemia
- increased CK, AST, and GGT
What gross and histologic pathology is seen in horses with glycogen branching enzyme deficiency (GBED)?
GROSS = no changes
HISTO = PAS stain of affected skeletal muscle, heart, and liver show basophilic inclusions in skeletal and cardiac muscles (inclusions in branched glycogen take up stain)
