JPC SYSTEMIC PATHOLOGY
MUSCULOSKELETAL SYSTEM
APRIL 2022
M-T02
Signalment (ACVP/75-25): 2-year-old red Angus cow
HISTORY: This is one of 14 surviving cows from a small herd in Southeast Texas. Sixteen cows died suddenly or after being down for less than 24 hours. The cows had grazed a coastal Bermuda grass pasture that contained toxic weeds. The cow was alert and had a good appetite but would not rise from sternal recumbency.
HISTOPATHOLOGIC DESCRIPTION: Skeletal muscle: 50% of myocytes are characterized by one of the following: swollen up to 100 um in diameter with pale, often vacuolated sarcoplasm, indistinct cross striations, and disrupted myofibrils (degeneration); shrunken and angulated with homogeneous, hypereosinophilic, hyalinized sarcoplasm, disorganized fragmented myofibrils, loss of cross striations, prominent contraction bands, and pyknotic nuclei (necrosis); or rarely, basophilic sarcoplasm with internalized, “rowed”, vesiculate nuclei (regeneration) . Multifocal aggregates of hyperplastic and hypertrophied satellite cells and macrophages surround and occasionally are intrasarcoplasmic within degenerate and necrotic myocytes.
MORPHOLOGIC DIAGNOSIS: Skeletal muscle, myocytes: Degeneration and necrosis, acute, multifocal, moderate, with rare regeneration, red Angus cow, bovine.
ETIOLOGIC DIAGNOSIS: Phytotoxic myopathy
CAUSE: Senna sp. (formerly Cassia sp.)
GENERAL DISCUSSION:
- Caused by ingestion of beans of senna or coffee occidentalis (Senna occidentalis or obtrusifolia) by goats, cattle, horses, and pigs
- occidentalis is an annual shrub found in the southeastern US and is believed to be the most toxic of the Senna species
- obtusifolia (sicklepod senna, Java bean), S. roemeriana (twin leaf senna), S. fistula (senna of commerce, golden shower tree), S. lindheimeriana, and S. tora are also toxic
- Frost makes the plant more palatable; more toxicoses reported late in the year
- Entire plant is toxic, but the seed tegument is most toxic component
PATHOGENESIS:
- Toxic principle is unknown
- Uncoupling of oxidative phosphorylation and depression of mitochondrial respiration within myocardial fibers > energy loss, cell swelling, and degeneration of the sarcotubular system
TYPICAL CLINICAL FINDINGS:
- Anorexia, diarrhea, hyperpnea, tachycardia
- Weakness rapidly progressing to ataxia, recumbency, and death
- Death is attributed to myocardial degeneration and necrosis and heart failure
- Clinical pathology:
- Myoglobinuria
- Elevated creatine phosphokinase (CK), aspartate aminotransferase (AST), lactate dehydrogenase (LDH)
- Hyperkalemia
TYPICAL GROSS FINDINGS:
- Skeletal muscle: poorly defined pallor of muscle mass; gross findings may be minimal in spite of histologic findings demonstrating degeneration
- Heart: Subendocardial to diffuse pale yellow mottling and streaking, +/- subepicardial hemorrhages (especially near coronary arteries), +/- pericardial effusion
- Lungs: Diffuse congestion and interlobular edema
- Trachea and bronchi: May be filled with serous to frothy fluid
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Skeletal muscle: Monophasic, multifocal, segmental myocyte degeneration and necrosis with intact sarcolemmal sheaths and muscle nuclei; usually no mineralization
- Myocardium: Initial small, indistinct vacuoles within myofibrils; progression to degeneration and necrosis
- Lungs: Edema and marked congestion
- Liver: Centrilobular fatty degeneration and necrosis (secondary to heart failure)
- Kidney: Tubular degeneration with protein casts
ULTRASTRUCTURAL FINDINGS:
- Mitochondrial swelling and disrupted or excessively branched mitochondrial cristae +/- electron-dense spherical inclusions within affected mitochondria
- Mitochondrial collapse, cellular swelling, glycogen loss
DIFFERENTIAL DIAGNOSIS: Other toxic myopathies and cardiomyopathies:
Causes of toxic myopathies +/- cardiomyopathies:
- Coyotillo (Karwinskia humboldtiana)
- Gossypol (cottonseed) (pigs especially affected)
- Lupine (Diaporthe toxica) (sheep)
- Water hemlock (Cicuta douglasii) (sheep)
- False lupine (Thermopsis montana) (calves)
- White snakeroot (Ageratina [formerly Eupatorium] rugosum) (horses, ruminants)
- Rayless goldenrod (Isocoma pluriflora) (horses, ruminants)
- Vitamin E / selenium deficiency (M-M11)
- Selenium toxicosis (pigs, cattle, sheep, others)
- Ionophore toxicosis (monensin, maduramicin, others; horses particularly susceptible) (M-T01)
Causes of toxic cardiomyopathies:
- Summer pheasant’s eye (Adonis aestivalis) (cardiac glycoside; endocardial hemorrhage)
- Oleander (Nerium oleander) (cardiac glycoside; southern and southwest US; most species susceptible)
Causes of toxic metastatic mineralization:
- Vitamin D containing plants (Cestrum diurnum, Trisetum flavescens, Solanum glaucophyllum [formerly malacoxylon]) (M-T01; metastatic mineralization)
COMPARATIVE PATHOLOGY:
- Senna toxicosis reported in cattle, sheep, goats, horses, pigs, poultry, and rabbits
- Pigs had no gross lesions, but microscopic degeneration in the heart and diaphragm with vacuolation and segmental hypercontraction of fibers
REFERENCES:
- Cooper BJ, Valentine BA. Muscle and Tendon. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. St Louis, MO: Elsevier; 2016: 219-220.
- Haraguchi M, Calore EE, Dagli MLZ, et al. Muscle atrophy induced in broiler chicks by parts of Senna occidentalis Vet Res Comm. 1998;22:265-271.
- Jones TC, Hunt RD, King NW. Diseases due to extraneous poisons. In: Veterinary Pathology. 5th ed. Baltimore, MD: Williams and Wilkins; 1997:770-771.
- Rissi DR, L Barros CS. Pathology in Practice. J Am Vet Med Assoc. 2017;250(1):51-53.
- Sebastian MM. Role of pathology in diagnosis. In: Gupta RC, ed. Veterinary Toxicology: Basic and Clinical Principles. Ney York, NY: Elsevier; 2007:1120.
- Valentine BA, Skeletal Muscle. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1025-1029.
