Musculoskeletal

Question 1

Describe the Obel method to grade laminitis in horses.

Answer 1

Obel grade. / Characteristics

1. Horse alternately and incessantly lifts the feet; lameness is not evident at the walk but a short, stilted gait is noted at the trot
2. Stilted gait at the walk but moves willingly; a foot may be lifted off the ground without difficulty.
3. Reluctant to move and resists attempts to have a foot lifted
4. Refuses to move, does it only if forced

Question 2

What gene is suspected to be related to malignant hyperthermia (MH)?

Answer 2

A mutation of the ryanodine receptor 1 gene, which is essential in skeletal muscle excitation-contraction coupling. More common in humans, pigs, and dogs, but has been documented as an autosomal dominant gene in Quarter Horses with MH.

Question 3

Mention the clinical signs of heat stress in llamas or alpacas.

Answer 3

Hyperthermia (often > 105° F), signs of respiratory distress, tachycardia, recumbency, increased muscle enzymes, and hypoproteinemia.

Question 4

What can predispose to hypokalemic myopathy in cows?

Answer 4

Anorexia and enhanced potassium excretion secondary to the administration of one or more doses of isoflupredone acetate to ketotic cows.

Isoflupredone acetate has glucocorticoid and mineralocorticoid activity, resulting in a decrease in mean plasma potassium concentration by 25% in 2 days (after a single 20 mg injection) and 46% by the third day after two injections.

Question 5

What are the clinical signs in cows with hypokalemic myopathy?

Answer 5

Clinical signs include severe weakness, recumbency, abnormal position of the head and neck, rumen hypomotility or atony, abnormal feces, anorexia, and tachycardia. Cardiac dysrhythmia is also common.

Diagnosis is based on clinical signs and a serum potassium of <2.5 mmol/L. Cows can also have ketosis, metabolic alkalosis, and increased serum CK and AST activities. Muscle biopsies reveal a vacuolar myopathy.

Question 6

How is myotonia congenita in goats acquired and what name is it commonly known as?

Answer 6

It is an autosomal dominant mutation in the skeletal muscle chloride channel (CLCN1). It is commonly known as fainting goats.

Question 7

How is HYYP acquired and what are the breeds commonly predisposed to it?

Answer 7

Is caused by an inherited defect in the skeletal muscle sodium channel. It is an autosomal dominant trait affecting Quarter Horses, American Paint Horses, Appaloosas, and Quarter Horse crossbred .

Question 8

What is the common signalment for immune-mediated polymyositis?

Answer 8

Quarter Horse (or QH cross) that are either < 8 years of age or > 16 years of age. In approximately one third, a triggering
factor appears to be exposure to S. equi or a respiratory disease

Question 9

How would you diagnose IMM?

Immune-mediated polymyositis

Answer 9

Muscle biopsy of epaxial and gluteal muscles. Biopsy will show lymphocyte vasculitis, angular atrophy, lymphocyte myofiber infiltration, fiber necrosis with macrophage infiltration, and regeneration.
Semitendinosus or membranous may also show evidence of atrophy and vasculitis.

The lymphocytic infiltrate seen, contains a high CD4:CD8 ratio with no evidence of IgG binding to myofibers.