Cardiomyopathy in dystrophin-deficient hypertrophic feline muscular dystrophy.

A colony of cats affected with hypertrophic feline muscular dystrophy was used to study the occurrence of cardiomyopathy associated with dystrophin deficiency. Affected male and female cats, obligate carrier females, and unaffected healthy littermates were followed from 12 weeks of age into adulthood. Thoracic radiography, 2-D echocardiography, and 2-D-derived M-mode echocardiography were performed at 3-month intervals until 12 months of age and regularly thereafter. From 9 months of age, all affected cats had larger hearts than normal and carrier animals. Left ventricular wall thickness in systole and in diastole and interventricular septal thickness in systole were greater in affected cats 12 months and older when compared with normal or heterozygous animals (P < .05). The myocardium of affected cats was diffusely hypoechoic and thickened. Multiple hyperechoic foci were in the myocardium and papillary musculature. Shortening fraction was normal in all cats. Changes seen in carrier females included enlargement and hyperechogenicity of the papillary musculature after the age of 2 years. Gross and light microscopic examination revealed left ventricular wall thickening with multiple foci of mineralization in 2 of 5 hearts from dystrophin-deficient cats. Although approximately 10% of the normal dystrophin amount was present in the skeletal muscle, dystrophin could not be detected in the myocardium. Early onset concentric myocardial hypertrophy was present in all adult cats. Lesions were mainly localized in the myocardium of the left ventricular free wall and interventricular septum, papillary musculature, and the endocardium. Clinical signs of heart failure developed only infrequently in cats with hypertrophic feline muscular dystrophy.

Lethal peracute rhabdomyolysis associated with stress and general anesthesia in three dystrophin-deficient cats.

Three cats affected with dystrophin deficiency and hypertrophic muscular dystrophy developed peracute rhabdomyolysis with a fatal outcome. Two cats were anesthetized with isoflurane for routine procedures and did not recover properly from the anesthetic procedure. One cat was manually restrained for an echographic examination and started staggering after a short struggle; its condition worsened, and it died. Blood chemistry findings included severe hyperkalemia, hyperphosphatemia, hypocalcemia, massive increases in creatine kinase, aspartate aminotransferase, and alanine aminotransferase concentrations, and high ion gap metabolic acidosis. Light microscopic evaluation of skeletal muscle revealed severe acute rhabdomyolysis with marked extensive necrosis of large groups of fibers and endomysial edema. These lesions were observed in many skeletal muscles but particularly in the masseter and supraspinatus muscles and in the diaphragm. Typical changes associated with dystrophin deficiency in cats were also noted. Histochemical analysis revealed that the dystrophin deficiency was associated with a decrease in the percentage of type 1 myofibers in all three cats. This change was marked in the 20-month-old cat and milder in the younger cats (6.5 and 8.5 months of age). Percentages of type 2A fibers were markedly decreased and percentages of type 2X fibers were markedly increased in the younger cats. Rhabdomyolysis has been reported in dystrophinopathic humans but not in other animal models of dystrophin deficiency. An increased sensitivity of the dystrophin-deficient sarcolemmal membrane to volatile anesthetic agents, stress, or intense muscular activity is suspected.