JPC Systemic Pathology
Signalment (JPC# 2370157): A 1-year-old spayed female domestic shorthair cat
History: This cat died unexpectedly 6 days after routine ovariohysterectomy.
Histopathologic description: Heart: Diffusely, expanding the endocardium of the left ventricle up to five times normal (50um) and infiltrating and separating subjacent myofibers, there is abundant eosinophilic beaded to fibrillar material (fibrin), hemorrhage, and clear space (edema), admixed with moderate numbers of fibroblasts, neutrophils, lymphocytes, plasma cells, macrophages, and eosinophilic cellular and karyorrhectic debris (necrosis). Multifocally, inflammatory cells infiltrate the underlying myocardium, expand the interstitium, and separate, surround, and replace cardiomyocytes that are occasionally either swollen and vacuolated (degenerate), or shrunken with hypereosinophilic sarcoplasm, loss of cross striations, and pyknotic nuclei (necrotic).
Morphologic diagnosis: Heart, left ventricle: Endocarditis, fibrinous, subacute, diffuse, moderate, with edema, hemorrhage, and multifocal myocarditis, domestic shorthair cat, feline.
Etiologic diagnosis: Idiopathic endocarditis
CONDITION: Endomyocarditis (EMC)
- Endomyocarditis (EMC) is a unique disease in cats, which is often fatal, because of inflammation of the left ventricular outflow tract
- Common in cats less than 4 years old
- May be an antecedent condition to restrictive cardiomyopathy (RCM), although a recent study did not find evidence of EMC in any cases of RCM
- RCM is also known as left ventricular endocardial fibrosis (LVEF)
- Unknown; often occurs within 3 months of stressful events
- EMC may progress to LVEF if the cat survives
- Predilection for male, neutered cats
- Thromboemboli are a common sequela
- Recent studies rule out panleukopenia as a potential cause, but suggest Bartonella as possibly involved
TYPICAL Gross findings:
- Enlarged heart, dilated left atria
- Left ventricular subendocardial hemorrhage
- White to gray fibrinous material adherent to the left ventricular endocardium, especially papillary muscles and left ventricular outflow tract
- Sometimes aortic thromboembolism
TYPICAL LIGHT Microscopic findings:
- Acute: Severe infiltration of neutrophils, lymphocytes, plasma cells and macrophages in the myocardium and endocardium
- Older lesions have marked fibroplasia and/or granulation tissue
- Typically limited to the left heart; most severe in the dorsal septal wall
- Concurrent interstitial pneumonia with hyaline membranes lining alveolar space
For cardiac disease in cats:
- Left ventricular endocardial fibrosis (LVEF) or restrictive cardiomyopathy (RCM): Older cats; endocardial thickening with mural thrombosis
- Dilated (congestive) cardiomyopathy: Bilateral enlargement of all heart chambers associated with dietary taurine deficiency in cats; carnitine deficiency in dogs
- Hypertrophic cardiomyopathy
- Marked hypertrophy of the ventricles, especially the left ventricle
- Cardiomyocyte hypertrophy and disarray of sarcomeres
- Hereditary in Persian cats
- Concentric, usually bilateral, ventricular hypertrophy
- Enlarged thyroid glands
- Endocardial fibroelastosis: Young Burmese, Siamese
- Differentiate from EMC by lack of inflammation
- Aortic stenosis, hypertension
- Systemic reactive angioendotheliomatosis: Intraluminal proliferation of spindle cells within vessels often involving the heart with resultant myocardial dysfunction
- EMC is unique to cats
- Ulcerative endocarditis: Distinct ulcerative lesion in the left atrium of dogs, associated with acute renal insufficiency
- Horses: Strongylus vulgaris larval migration
- Bovine: Arcanobacter pyogenes
- Pigs: Streptococcus sp. and Erysipelothrix rhusiopathiae
- Dogs and Cats: Streptococcus sp. and coli
- In dogs, the most commonly recognized cardiomyopathy is the dilated or congestive form in giant and large-breed dogs. HCM is much less common than the dilated form
- In cattle, cardiomyopathies have been described in certain breeds (Japanese black cattle, Australian polled Herefords and Holstein-Friesian); inheritance is autosomal recessive
- Dilated and hypertrophic cardiomyopathies have been described in pigs
- An inherited cardiomyopathy exists in certain strains of Syrian hamsters causing atrial thrombosis.
- Mice – frequently get atrial thrombosis; left auricle is most commonly affected; precipitated by multisystemic amyloidosis, also common in BALB/C; left heart failure due to atrial thrombosis most common cause of noninfectious dyspnea in mice
- Guinea pigs – cardiac glycogenosis (rhabdomyomatosis) – considered an incidental finding; seen grossly as pale streaks in the heart most commonly in the left ventricle – composed of numerous vacuolated myofibers; the vacuoles contain glycogen; related to disorder of glycogen metabolism and possibly related to scurvy
- Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Wiley Blackwell; 2016: 99, 241-242.
- Donovan TA, et al. Bartonella as a possible cause or cofactor of feline endomyocarditis-left ventricular endocardial fibrosis complex. J Comp Pathol. 2018;162:29-42.
- Kimura Y, et al. Pathological features and pathogenesis of the endomyocardial form of restrictive cardiomyopathy in cats. J Comp Pathol. 2016;155(2-3):190-198.
- McEndaffer L, Molesan A, Erb H, Kelly K. Feline panleukopenia virus is not associated with myocarditis or endomyocardial restrictive cardiomyopathy in cats. Vet Pathol. 2017;54(4):669-675.
- Miller LM, Van Vleet JF, Gal A. Cardiovascular system and lymphatic vessels. In: Zachary JF, McGavin MD eds. Pathologic Basis of Veterinary Disease. 5th ed. St. Louis, MO: Elsevier Mosby; 2012: 588.
- Robinson WF, Robinson WF. Cardiovascular system. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. Louis, MO: Elsevier; 2016: 46-47.