Cushing's Myopathy in Dogs: Prevalence, Clinical Abnormalities, and Response to Treatment

A distinct myotonia is a muscle disorder that may occur secondary to excess corticosteroids (hyperadrenocorticism, HAC, or Cushing's disease) and is associated with electrodiagnostic abnormalities on electromyography (EMG). Clinically these disorders cause muscle stiffness, weakness, atrophy, and/or contractures, which can severely limit the quality of life of those affected. To date, there are very few published data regarding the onset, development, and treatment of hyperadrenocorticism-associated myotonia/pseudomyotonia. This is a multi-institutional retrospective study describing the clinical signs, diagnosis, and treatment of HAC-associated myotonia/pseudomyotonia. We found that this disorder was and continues to be rare. It most commonly occurs in adult dogs with chronic steroid exposure secondary to pituitary-dependent HAC. No cases of adrenal dependent HAC were identified in this population. In addition to muscle stiffness, dermatologic disease and liver enzyme abnormalities were common. A wide variety of therapeutic strategies, including polypharmacy and physical rehabilitation, were implemented, with little success. Analgesics were the most frequently administered type of medication.