Musculoskeletal System
March 2019

Signalment (JPC #2984049):  Two-year-old male weimaraner, Canis familiaris

HISTORY:  This dog was thin with atrophy of all muscles except those of the neck and tongue.  At necropsy, neck muscles were thick, giving a “buffalo hump” appearance.  The diaphragmatic muscle surrounding the central tendon was pale and 1.5 cm thick.  The body muscle mass was reduced and muscles were diffusely pale.

HISTOPATHOLOGIC DESCRIPTION:  Skeletal muscle, diaphragm:  The diaphragm is diffusely thickened (up to five times normal when compared with the control tissue), with disorganized, shortened myofibers that vary significantly in size and orientation. Diffusely, myocytes undergo one of the following changes: degeneration, necrosis, rare regeneration, or hypertrophy.  Multifocally, degenerate myocytes are characterized by swollen and vacuolated sarcoplasm with loss of cross-striations; necrotic myocytes exhibit shrunken, angular, hypereosinophilic, fragmented sarcoplasm, with contraction bands, pyknotic nuclei, multifocal mineralization and scattered infiltration by moderate numbers of macrophages; and regenerative myocytes contain small amounts of basophilic sarcoplasm and numerous linearly arranged internalized nuclei ("rowing") with prominent satellite cell nuclei at the cell margins.  Remaining myocytes are often hypertrophic with abundant sarcoplasm and several internalized nuclei.  Multifocally, there is loss of myofibers with replacement by fibrous connective tissue, often surrounding atrophied myofibers, which exhibit shrunken, hypereosinophilic sarcoplasm.  Multifocally the endomysial and perimysial connective tissue is expanded by moderate amounts of collagenous connective tissue and fibroblasts (fibrosis) admixed with few lymphocytes and plasma cells.  There is multifocal infiltration of adipocytes.

Skeletal muscle, diaphragm, unaffected age-matched control:  No significant lesions.

MORPHOLOGIC DIAGNOSIS:  Skeletal muscle, diaphragm:  Myocyte degeneration, necrosis, regeneration, and hypertrophy, diffuse, severe, with fibrosis and mineralization, weimaraner, (Canis familiaris), canine.

ETIOLOGIC DIAGNOSIS: Congenital muscular dystrophy

CAUSE:  X-linked dystrophin gene deficiency










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