Diseases Of Muscle p1277-1308

Question 1

What are three biochemistry values that can be used to evaluate muscle activity?

A) AST, GGT, SDH
B) ALP, CK, SDH
C) CK, GGT, LDH
D) AST, CK, LDH

Answer 1

D) AST, CK, LDH

CK is the most sensitive indicator of myonecrosis, as it is found in skeletal muscle and cardiac muscle. It rises quickly with muscle disruption and peaks 4-6 hours after insult. AST is found in skeletal muscle, cardiac muscle, as well as in RBCs, liver and other tissues. It rises as long as 24 hours after insult, slowly.

Question 2

When should blood samples be taken after exercise testing a horse for muscle disorders? How are results interpreted?

Answer 2

Samples should be taken before and 4-6 hours after exercise. Healthy horses should not see more than than a 3 fold increase in CK activity, after 15-30 minutes of light exercise. 5 fold increases are evidence of exertional rhabdomyolysis.

Question 3

Define myotonic muscle disorders.

Answer 3

Myotonic muscle disorders are those that feature delayed relaxation of muscle after mechanical stimulation or voluntary contraction.

Question 4

Describe 2 myotonic-like diseases. One in cattle and one in horses. These disease do not have myotonic discharges noted on electromyography.

Answer 4

Spastic paresis, or Elso heel, is seen in cattle. Calves between 2 and 7 months of age have straight angles of hock and stifle. There is a decreased capacity of inability to flex the hock. Continuous tension of the gastrocnemius prevents this movement and can be unilateral and bilateral.

Shivers is the condition in horses characterized by involuntary spasms of the muscles in the pelvic region, pelvic limbs and tail. Exacerbated when horse is backed, seen by elevation of limb, abduction and then shaking and shivering in the air for several seconds.

Question 5

Myotonia congenita caused by an autosomal dominant mutation in the skeletal muscle chloride channel CLCN1, with incomplete penetrance, is found in which species?

A) Ponies
B) Cattle
C) Goats
D) Sheep

Answer 5

C) Goats

These goats are known as “fainting goats,” and signs are seen by 6 moths of age.

Question 6

How is myotonia definitively diagnosed?

Answer 6

Diagnosis of myotonia is based on results of EMG, with pathognomonic crescendo-decrescendo high-frequency repetitive bursts, characteristic dive-bomber sound. This sound is created by the repetitive firing of affected muscle fibers.

Question 7

Describe the etiology of HYPP.

Answer 7

Hyperkalemic periodic paralysis is caused by a point mutation resulting in a phenylalanine/leucine substitution in the voltage dependent skeletal muscle sodium channel alpha subunit. When there is an elevation in extra cellular K+, this causes Na+ to influx, and the abnormal Na+ channels are unable to be inactivated. This leads to persistent depolarization of muscle cells and temporary weakness.

Question 8

Distinguish which of these definitions describes muscle cramping vs muscle contracture.

A) hyperactivity of motor units caused by repetitive firing of the peripheral and/or CNS; originating in most cases in the IM portion of the motor nerve terminal; induced by changes in electrolyte composition of extra cellular fluid, or by ear tick infestations in horses

B) painful spasms unaccompanied by depolarization; seen in malignant hyperthermia and exertional myopathies

Answer 8

A) Muscle cramps are a painful condition arising from hyperactivity of motor units caused by repetitive firing of the peripheral and/or CNS; originating in most cases in the IM portion of the motor nerve terminal; induced by changes in electrolyte composition of extra cellular fluid, or by ear tick infestations in horses

B) Muscle contractures are painful spasms that represent a state of muscle contracture unaccompanied by depolarization; seen in malignant hyperthermia and exertional myopathies

Question 9

When treating a horse for during an episode of HYPP, which of the following is responsible for raising of muscle membrane threshold potential decreasing membrane hyperexcitability.

A) Acetazolamide
B) Sodium bicarbonate
C) Dextrose
D) Calcium gluconate

Answer 9

D) Providing calcium gluconate increases the extracellular concentration of Ca2+, leading to the desired effects.

Providing dextrose increases stimulation of insulin and encourages decrease of extracellular potassium.

Acetazolamide is responsible for stabilizing blood glucose and consequently serum potassium levels.

Sodium bicarbonate also helps with intracellular movement of potassium.

Question 10

What is the classical clinical sign of thumps, in horses?

A) Irregularly regular respiration rate
B) Flank contraction synchronous with the heart
C) Intermittent abdominal tuck
D) Apparent jugular pulse

Answer 10

B) Thumps, aka synchronous diaphragmatic flutter, is most notably seen with hypocalcemia, associated with hypochloremic metabolic alkalosis.

Question 11

Describe the two possibly etiologies that Strep. equi may cause an acute bout of rhabdomyolysis.

Answer 11

1) Toxic shock-like reaction from nonspecific T cell stimulation by streptococcal superAg with release of high levels of inflamm cytokines
2) Bacteremia with local multiplication and production of exotoxins or proteases within skeletal muscles;

Question 12

How high is the titer to the M protein, in horses with acute rhabdomyolysis associated with Strep. equi?

A) Extremely high
B) Low
C) Non-existent
D) Variable

Answer 12

Titers to S. equi are generally low, in horses with acute rhabdomyolysis, unless the horse has recently been vax for strangles.

Question 13

What antibiotic has been reported to be related to a high mortality rate in horses with clinical signs of strangles and myopathy? What additional antibiotic that helps inhibit protein synthesis could be added to enhance survival rates in horses with S. equi rhabdomyolysis?

A) IV penicillin, rifampin
B) IV aminoglycoside, rifampin
C) IV penicillin, chloramphenicol
D) IV aminoglycoside, chloramphenicol

Answer 13

A) IV penicillin, rifampin

A mortality rate of 85% has been reported in people despite penicillin treatment.

Question 14

Which of the following IS NOT an inciting cause of infective purpura hemorrhagica, related to S. equi?

A) Exposure to S. equi within 3 weeks of presentation
B) Vaccination against strangles
C) 2 weeks post-infection of strangles
D) Concurrent Salmonella infantum infections

Answer 14

C) 2 weeks post-infection of strangles IS NOT an inciting cause of infective purpura hemorrhagica (IPH).

Question 15

What are the immune complexes most often made of, in cases of infarctive purpura hemorrhagica?

A) IgM, IgG and M protein
B) IgA, IgG and M protein
C) M protein, IgA, IgM
D) M protein, IgE, IgA

Answer 15

C) M protein, IgA, IgM

These complexes are what lead to the infarctive nature of this disease, leading to cell membrane destruction, cell death and vascular occlusion.

Question 16

Approximately 1/3 of horses with immune mediated polymyositis have a triggering factor of exposure to S. equi or respiratory disease. Whic of the following describes the characteristics of the lymphocytic infiltrate seen in the muscle samples from horses with IMM?

A) Low CD4:CD8 ratio, excess IgG binding
B) Low CD4:CD8 ratio, no IgG binding
C) High CD4:CD8 ratio, excess IgG binding
D) High CD4:CD8 ratio, no IgG binding

Answer 16

D) High CD4:CD8 ratio, no IgG binding

Question 17

The life cycle of Sarcocystis involves:

A) 1 definitive carnivore host
B) 1 definitive carnivore host and 1 intermediate cattle/horse host
C) 1 definitive cattle/horse host
D) 1 definitive cattle/horse host and 1 intermediate carnivore host

Answer 17

B) 1 definitive carnivore host and 1 intermediate cattle/horse host

Question 18

What level of sporocyts are needed to cause severe clinical disease of Sarcocystis cruzi in cattle?

A) 100
B) 40,000
C) 500,000
D) 200,000

Answer 18

D) 200,000

Question 19

What are the two forms of nutritional myodegeneration and how do they present?

Answer 19

Cardiac form has a sudden onset and a high mortality rate. C/s are weakness, resp distress, rapid irregular HR, death within 24 hours.

Skeletal form has a slow onset and can be responsive to treatment. These animals have muscle weakness, stiffness, pain on palpation. Improvement can be see after a few days and within 3-5 days animals can be standing and walking again.

Question 20

Why are selenium and Vitamin E so important for cellular health?

Answer 20

These are important for cellular integrity. Selenium is an important component of many selenoproteins, glutathione-peroxidase (GSH-Px). Vitamin E serves as a free radical scavenger.

As a free radical scavenger, Vit E prevents the formation lipid hydroperoxidases. GSH-Px destroys hydrogen peroxidase and lipoperoxidases and converts them to H2O and harmless alcohols.

Question 21

What is the role of polyunsaturated fatty acids (PUFAs) in development of nutritional myodegeneration (NMD)?

Answer 21

PUFAs come from pasture grasses and plants during their active growing periods. PUFAs from the diet can undergo peroxidation to hydroperoxidases, and create free radicals. If an animal is already deficient in free radical scavengers or destroyers, then they can quickly develop NMD. Seen often in calves or lambs put out to pasture early, especially if their dams are deficient.

Question 22

What are some toxic causes of rhabdomyolysis?

Answer 22

Ionophores, chemical toxins (reports with lidocaine, diazepam, digoxin, levamisole, nitroclofene, pentazocine, thiazinamium, chloramphenicol, nitroclofene, oxytet), plants (gossypol, Cassia spp and tremetone-containing plants, Eupatorium rugosum [white snakeroot], Isocoma wrightii [rayless goldenrod])

Question 23

How do Acer negundo and Acer pseudoplatanus cause seasonal pasture myopathy and atypical myopathy?

Answer 23

Box elder and European sycamore maple, respectively, contain the toxin hypoglycin A, which is metabolized in the liver and binds irreversibly to acyl CoA dehydrogenase enzymes. This then prevents metabolism of short and medium-chain FA and branched chain AA. This accumulation of fat esters damages muscle cells, creates a energy deficiency and results in a lipid storage myopathy.

Question 24

What distinguishes PSSM 1 from PSSM 2?

A) PSSM 2 has two ways of being diagnosed: genetic testing and muscle biopsy
B) PSSM 1 has an autosomal dominant mutation in the RYR1 gene
C) In the acute form of PSSM 2, horses generally show clinical signs when they are calm, with muscle fasiculations, tucking of the abdomen and muscle stiffness.
D) The well understood mechanism of PSSM 1 includes the horses’ reduced ability for fatty acid oxidation, increased muscle citrate concentrations and inhibition of carnitine palmitoyltransferase.

Answer 24

D)

PSSM 1 can be diagnosed with 2 diagnostics, genetic testing from hair follicles or blood. PSSM 1 has been found to be due to an autosomal dominant gene mutation (single-base-pair mutation) in the GYS1 gene, causing an arginine to histidine substitution at codon 309. PSSM 2 cannot be determined by genetic testing, bc the underlying cause for it has not been determined.

Muscle biopsies of both types show an abnormal accumulation of glycogen, with subsarcolemmal vacuoles. (Periodic acid-Schiff positive).

In both types, there is an acute and chronic presentation. PSSM 1 acute often occurs in calm quiet animals with muscle fasciculations, firm muscle contracture. PSSM 1 chronic occurs in riding horses as lack of energy under saddle, reluctance to move, sour attitude toward riding. PSSM 2 acute is similar, but does not have the same calm temperament. Muscle atrophy is a common complaint. PSSM 2 are more related to poor performance over episodes of rhabdomyolysis.

The pathophys behind PSSM 1 is contributed to the gene mutation in conjunction with animals that are being fed non-structured carbohydrates. NSC diets can limit acetyl CoA for oxidative metabolism. These horses also have low plasma [NEFAs], possibly due to suppression of lipolysis from high insulin levels. Another factor is high muscle [citrate], directing acyl CoA from the citric acid cycle toward malonyl CoA. This causes inhibition of carnitine palmitoyltransferase, an enzyme needed to transport long chain fatty acids into the mitochondria for beta-oxidation.