Disorders of muscle

Question 1

How frequent are muscle disorders in cats

Answer 1

Muscle disorders are uncommon in cats

Question 2

What are the most common causes of myopathy in cats

Answer 2

The most common causes of myopathy can be divided into:
- inflammatory causes
- infectious (e.g., toxoplasmosis, clostridium)
- noninfectious (i.e., immune-mediated) (e.g., associated with thymoma, myasthenia gravis, lymphoma)

- noninflammatory
    - primary (i.e., congenital/inherited diseases)
    - secondary
        - metabolic (e.g., hypokalemia, hyperthyroidism, hypocalcemia, hypernatremia)
        - ischemic (e.g., thromboembolic disease associated with congestive heart failure)
        - toxic (e.g., pyrethrins, organophosphates)

Question 3

What are the common clinical signs to myopathies

Answer 3

Clinical signs include:
- weakness
- stiffness
- myalgia
- muscle atrophy or hypertrophy

Question 4

What is an important differential to consider in face of an elevated CK before concluding to a myopathy

Answer 4

Serum CK levels can be significantly elevated in anorexic cats
- so results must be interpreted cautiously considering the patient’s recent nutritional history

Question 5

What are the key features for hypokalemic myopathy of Burmese cats

Answer 5

It is characterized by episodic muscle weakness associated withe intermittent hypokalemia
- but hypokalemia may not be synchronous with clinical signs

Clinical signs of severe generalized muscle weakness, including neck ventroflexion, head-bobbing, and dorsal protrusion of the scapulae, may be trigerred by stress or exercise
- clinical signs generally first appear between 2 and 6 months of age

Pathomechanism:
- the disorder is due to an autosomal recessively inherited mutation in the WNK gene
- the mechanism is suspected to be a potassium-losing nephropathy

Treatment:
- potassium ssupplementation

Question 6

What are the key features of congenital myotonia

Answer 6

Congenital myotonia is characterized by prolonged muscle contraction after cessation of voluntary effort

Pathomechanism:
- it is believed to be due to a chloride channel abnormality inherited as an autosomal recessive trait (mutation in CLCN1 gene encoding for chloride channels in skeletal muscle)

Clinical signs:
- difficulty opening the mouth
- muscle hypertrophy
- stiff gait with the stiffness decreasing during exercise

Question 7

Give some examples of diseases that may give rise to potassium-depletion myopathy

Answer 7

Renal disease

Vomiting and/or diarrhea

Hyperaldosteronism

Postobstructive diuresis

Diuretic administration

Inappropriate fluid therapy

Diabetic ketoacidosis