JPC SYSTEMIC PATHOLOGY
Musculoskeletal System
March 2019
M-M06

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

GENERAL DISCUSSION:

PATHOGENESIS:

TYPICAL CLINICAL FINDINGS:

TYPICAL GROSS FINDINGS:

TYPICAL LIGHT MICROSCOPIC FINDINGS:

ULTRASTRUCTURAL FINDINGS:

DIFFERENTIAL DIAGNOSIS:

COMPARATIVE PATHOLOGY:

REFERENCES:

  1. Baroncelli AB, Abellonio F, Pagano TB, et al. Muscular dystrophy in a dog resembling human Becker muscular dystrophy. J Comp Pathol. 2014; 150(4):429-433.
  2. Cooper BJ, Valentine BA. Muscle and tendon. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. St. Louis, MO: Elsevier; 2016:167,173-200.
  3. Hall RL, Bender HS. Muscle. In: Latimer KS, ed. Duncan and Prasse’s Veterinary Laboratory Medicine Clinical Pathology. 5th Ames, IA: Wiley-Blackwell; 2011: 286-289.
  4. Leininger JR. Skeletal muscle. In: Maronpot RR, Boorman GA, Gaul BW, eds. Pathology of the Mouse. Vienna, IL: Cache River Press; 1996:638-639.
  5. Matsumotos H, et al. The ubiquitin ligase gene (WWP1) is responsible for the chicken muscular dystrophy. FEBS Letters 2008;582:2212-2218.
  6. Remmers G, Hayden DW, Jaeger MA, Ervasti JM, Valberg SJ. Postanesthetic death in a cat with myopathy. Vet Pathol. 2015; 52(1):186-188.
  7. Saito F, et al. Aberrant glycosylation of alpha-dystroglycan causes defective binding of laminin in the muscle of chicken muscular dystrophy. FEBS Letters 2005;579:2359-2363.
  8. Valentine BA. Skeletal muscle. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease, 6th ed. St. Louis, MO: Elsevier; 2017:914-922,928,944-952.
  9. Wilson K, Faelan C, Patterson-Kane JC, et al. Duchenne and Becker Muscular Dystrophies: A Review of Animal Models, Clinical End Points, and Biomarker Quantification. Tox Path. 2017;45(7):961-967.
  10. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. Ames, IA: John Wiley & Sons, Inc.; 2016: 105,115.


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