Myopathy associated with hyperadrenocorticism in the dog

Area of Science:

• Veterinary Medicine
• Neurology
• Endocrinology

Background:

• Hyperadrenocorticism (Cushing's disease) is a common endocrine disorder in dogs.
• Myopathy, a disease of the muscles, can manifest as weakness or stiffness.
• The link between hyperadrenocorticism and myopathy requires further investigation.

Purpose of the Study:

• To investigate the association between hyperadrenocorticism and myopathy in dogs.
• To characterize the clinical, electrodiagnostic, and histopathological findings of myopathy in affected dogs.
• To evaluate the response of myopathy to treatment of hyperadrenocorticism.

Main Methods:

• Case series involving six dogs with naturally occurring or iatrogenic hyperadrenocorticism.
• Clinical examination, including assessment of muscle strength and size.
• Electromyography (EMG) to evaluate muscle electrical activity.
• Muscle biopsy for histopathological, electron microscopic, and histochemical analysis.

Main Results:

• Six dogs presented with signs of myopathy, including muscle weakness, atrophy, stiffness, and proximal muscle enlargement.
• Electromyography revealed myotonic discharges in five dogs; one dog had normal EMG findings.
• Histopathological examination confirmed a noninflammatory degenerative myopathy.
• Five of six dogs showed improvement in clinical signs after treatment for hyperadrenocorticism.

Conclusions:

• Hyperadrenocorticism is associated with a distinct noninflammatory degenerative myopathy in dogs.
• Myopathy in these cases is characterized by specific clinical and electrodiagnostic findings.
• Treatment of the underlying hyperadrenocorticism can lead to clinical improvement of the myopathy.