Muscular Dystrophies in Dogs and Cats

Muscular dystrophy is a type of degenerative and/or developmental myopathy affecting dogs and cats.

The most common forms of muscular dystrophy in both humans and animals are associated with deficiencies of the protein dystrophin, which is located on the X chromosome. X-linked dystrophin-deficient muscular dystrophies in dogs and cats are thought to be the analogues of Duchenne and Becker muscular dystrophies in humans, respectively, and have been described in numerous dog and cat breeds. Specific genetic mutations have been identified in Golden Retrievers, German Shorthaired Pointers, Cavalier King Charles Spaniels, Japanese Spitz dogs, Rottweilers, and Brittanys, among others (1). Muscular dystrophy is best described in the Golden Retriever (2).

The predominant clinical sign in dogs is progressive muscular atrophy, whereas muscular hypertrophy is the hallmark of X-linked muscular dystrophy in cats. Both atrophy and hypertrophy can occur in both species, and all muscles are not uniformly affected (see hypertrophic thoracic muscles image).Partial trismus and a "bunny-hopping" gait have been observed in male dogs as young as 6 weeks old.

Other common clinical signs of muscular dystrophy in dogs and cats include the following:

• exercise intolerance

• stilted gait

• plantigrade stance

• dysphagia (see dysphagia image and dysphagia video)

• dysphonia

• kyphosis that progresses to lordosis

• hypertrophy of the muscles at the base of the tongue

There are a variety of muscular dystrophies with variable disease progression. Juvenile-onset cases may be more severe, whereas adult-onset cases may have a milder disease course. In Golden Retrievers, clinical signs typically progress over 3–6 months, after which time the disease progresses more slowly. Marked increases in serum CK activity are detected within a few weeks after birth.

Dystrophin-deficient muscular dystrophy, dysphagia, dog (Brittany)

Image

Courtesy of Shinichi Kanazono, DVM, DACVIM (Neurology).

Dystrophin-deficient muscular ...

video

Suspected muscular dystrophy, hypertrophic thoracic muscles, dog

Image

Courtesy of Carrie Jurney, DVM, DACVIM (Neurology).

Feline X-linked muscular dystrophy is much more variable. Clinical signs in affected cats include the characteristic "bunny-hopping" gait in the first few months of life; however, they can also appear clinically unaffected or only mildly affected until approximately 2 years old. Cats demonstrate a progressive stiffness in their gait and muscle hypertrophy. Stress can lead to open-mouthed breathing or syncopal episodes as a result of a combination of cardiac and respiratory muscle involvement.

Diagnosis of muscular dystrophy is based on the following:

• signalment

• characteristic clinical signs

• marked serum CK activity elevation (often > 10,000 U/L)

• abnormal electromyographic findings

• muscle biopsy results

Consistent radiographic abnormalities have been identified in Golden Retrievers with X-linked muscular dystrophy. Thoracic radiographic images show diaphragmatic asymmetry, which may accompany a hiatal hernia. Pelvic radiographs show the pelvis is tilted vertically, narrowed, and elongated.

There is no definitive treatment for any of the muscular dystrophies. Some patients have an unexplained response to glucocorticoid treatment. A favorable response to prednisone, 1–2 mg/kg, PO, every 24 hours, has been reported (3, 4); however, the improvement is short-term. Duration of treatment is unknown but is unlikely lifelong, as a sustained response to steroids does not occur.

Overall, the prognosis for dogs and cats with muscular dystrophies is guarded to poor, and disease severity varies.

For other degenerative and/or developmental myopathies in dogs and cats, see the Overview for this chapter.