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676.e2 Myopathies, Noninflammatory

Myopathies, Noninflammatory
VetBooks.ir Advanced or Confirmatory Testing

○ Ventroflexion of the head (very prominent
BASIC INFORMATION
in cats) • Genetic testing is available for inherited
Definition ○ Dysphagia possible myopathies in certain breeds
Noninflammatory myopathies include con- • In cases of muscular dystrophy, dogs tend to • Muscle biopsy: histopathology with special
genital and acquired muscle disorders. Muscular have muscle atrophy in majority of muscle stains to identify abnormality
dystrophies are a diverse group of inherited, groups, with hypertrophy of select muscles • Electrodiagnostics: abnormalities on electro-
degenerative noninflammatory diseases causing (i.e., semimembranous, semitendinous, and myography with normal nerve conduction
specific deficits of muscle constituents. Meta- tongue). Muscular dystrophy causes general- studies can help differentiate myopathy from
bolic and endocrine myopathies can involve ized muscular hypertrophy in cats. neuropathy.
symptoms of muscular dysfunction secondary to • Cold weather can exacerbate clinical signs.
an underlying hormonal or metabolic disease. TREATMENT
Etiology and Pathophysiology
Epidemiology • Inherited/degenerative myopathies Treatment Overview
SPECIES, AGE, SEX ○ Genetic predisposition • For the degenerative and inherited myopa-
• Muscular dystrophy (dystrophic form) tends ○ Disruption of muscular structural support thies, there are no specific treatments avail-
to affect young (<2 years old), male dogs and and functional components able; some anecdotal information indicates
rarely affects cats. • Metabolic/endocrine myopathies that nutritional supplements (L-carnitine,
• Metabolic and endocrine myopathies can ○ Hypokalemic myopathy causes muscle coenzyme Q 10 , B vitamins) can help.
affect dogs or cats of any age. membrane hyperpolarization. • For the metabolic and endocrine myopa-
○ Hyperadrenocorticoid (Cushing’s) or thies, treatment of the underlying cause is
GENETICS, BREED PREDISPOSITION steroid myopathy thought to be due to indicated.
Inherited myopathies have been reported in interference with muscle fiber mitochon-
many breeds. The mutation has been character- drial function Acute General Treatment
ized, and genetic testing is available for ○ Hypothyroid myopathy is likely due to • Hypokalemic myopathy
• Centronuclear myopathy: Labrador retriever, abnormalities in metabolism of the muscle ○ Potassium gluconate 5-8 mEq/kg/day
Great Dane cell. for 1-3 days (until normal potassium
• Dystrophin-deficient muscular dystrophy: levels), then 2-4 mEq/day (if required)
golden retriever, Cavalier King Charles DIAGNOSIS (p. 516)
spaniel, Japanese spitz, and Pembroke Welsh • Hyperadrenocorticoid (Cushing’s) or steroid
corgi Diagnostic Overview myopathy
• Myotonia congenita: miniature schnauzers, After localizing to the lower motor neuron ○ Treatment for hyperadrenocortisolism
Australian cattle dog based on the neurologic exam, perform initial (e.g., trilostane)
diagnostic testing to assess underlying metabolic ○ Stop glucocorticoid medication for
RISK FACTORS or inflammatory causes. Additional testing with iatrogenic myopathy
Hyperadrenocorticism, hypothyroidism, electrodiagnostics and muscle biopsy should • Hypothyroid myopathy: start thyroid
electrolyte disturbance be considered. Genetic testing is available for supplementation
some of the inherited myopathies.
Clinical Presentation Possible Complications
DISEASE FORMS/SUBTYPES Differential Diagnosis • Regurgitation and aspiration pneumonia with
• Inherited/degenerative myopathies (rare) • Inflammatory involvement of pharyngeal and esophageal
○ Muscular dystrophy (golden retrievers and ○ Autoimmune myositis muscles.
other dogs and cats) ○ Protozoal myopathies (toxoplasmosis or • Muscular dystrophy is often associated with
○ Centronuclear myopathies (Great Danes neosporosis) cardiomyopathy.
and Labrador retrievers) • Neoplasia • Dystrophic cats are prone to a malignant
○ Myotonia congenital (chow chow, min- • Trauma hyperthermia–like syndrome.
iature schnauzer, and other breeds) • Toxicity
• Metabolic/endocrine myopathies (common) PROGNOSIS & OUTCOME
○ Hypokalemic myopathy Initial Database
○ Hyperadrenocorticoid (Cushing’s) or • Neurologic exam (p. 1136): evidence of lower • Poor for inherited/degenerative myopathies
steroid myopathy motor neuron disease • Varies for metabolic and endocrine myopa-
○ Hypothyroid myopathy • Creatinine kinase > 1000 UI/L: indicates a thies; generally good if underlying cause
myopathy-causing myocyte injury identified and addressed
HISTORY, CHIEF COMPLAINT • Lactic acid > 6.0 mmol/L (before and after
Weakness (paresis) and muscle atrophy are 10 minutes of exercise): indicates metabolic PEARLS & CONSIDERATIONS
most common. myopathies or centronuclear myopathies
• Potassium < 3.5 mEq/L: indicates hypoka- Comments
PHYSICAL EXAM FINDINGS lemic myopathy A normal serum creatinine kinase (CK) does
• Most cases show evidence of lower motor • Cortisol (before and after low-dose dexa- not rule out muscle disease.
neuron signs. methasone or ACTH stimulation): to
○ Muscle atrophy evaluate for hyperadrenocorticoid myopathy Prevention
○ Paresis (p. 485) Genetic counseling for breeders of dogs
○ Decreased or absent reflexes • Thyroid panel: to evaluate for hypothyroid- that have had congenital myopathy in the
○ Plantigrade/palmigrade stance ism (p. 525) pedigree.

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