JPC SYSTEMIC PATHOLOGY

CARDIOVASCULAR SYSTEM

April 2022

C-M03 (NP)

 

Signalment (JPC #1713374):  9-week-old female Siamese cat

 

HISTORY:   This cat presented with severe dyspnea.

 

HISTOPATHOLOGIC DESCRIPTION:  Heart:  Diffusely the endocardium is uniformly thickened up to 200 to 250 um (20x normal) by numerous fibrocytes, fewer fibroblasts, and many layers of collagen and elastic fibers (fibroelastosis). Superficially, fibers are thin, loosely and randomly arranged, and separated by increased clear space and scant myxomatous matrix. Fibers within the deeper layers are thicker, more tightly packed, and are parallel. Multifocally the fibroelastic connective tissue extends minimally into the underlying myocardium, rarely surrounding and isolating myofibers and Purkinje fibers.

 

MORPHOLOGIC DIAGNOSIS:  Heart, endocardium:  Fibroelastosis, diffuse, marked, Siamese, feline.

 

CONDITION:   Endocardial fibroelastosis (EFE)

 

GENERAL DISCUSSION:

• Rare, congenital, inherited disease that primarily affects Burmese and Siamese cats leading to early onset of congestive heart failure (CHF) and death; rarely affects dogs
• Diffuse endocardial thickening by collagen and elastic fibers without other significant cardiac lesions

 

PATHOGENESIS:

• Unknown
• A developmental reaction:
  • Characterized by smooth muscle hyperplasia and fibroplasia at the inner 4^th and 5^th layers of the endocardium
  • Result of different pathologic conditions leading to decreased myocardial motility
• In affected Burmese kittens: Lesions visible microscopically at 1 day of age and grossly by 20 days of age 
  • Initial localized endocardial lymphedema (suggests obstruction of cardiac lymphatics) with subendocardial proliferation of fibroblasts; progresses to collagen and elastin deposition
• Degeneration of entrapped Purkinje fibers (left bundle branch) may lead to cardiac conduction abnormalities 

 

TYPICAL CLINICAL FINDINGS:

• Short disease course with dyspnea, cyanosis, pulmonary congestion, hydrothorax, hepatic congestion, ascites, tachycardia, heart murmurs, tachypnea, often sudden death
• Mildly affected animals may reach adulthood and reproduce

 

TYPICAL GROSS FINDINGS:

• Left atrium and ventricle (right heart only rarely involved):
  • Endocardium thickened, silver to white (“porcelain-like”), glistening due to the proliferation of fibroelastic tissue 
  • Dilation of LA and dilation and hypertrophy of LV without any associated cardiac malformation 
• Cardiomegaly, hydropericardium, hydrothorax with chronicity (secondary to CHF)

 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

• Endocardium intact and thickened by layers of collagen and elastic fibers
• Endocardial edema with dilated lymphatics; no fibrin or inflammation
• Superficial layers:  Fibers are thin and haphazardly oriented
• Deeper layers:  Fibers are thick, well organized, and parallel
• Purkinje fibers can become entrapped and undergo degeneration

 

ADDITIONAL DIAGNOSTIC TESTS:  

 

DIFFERENTIAL DIAGNOSIS:

• Secondary EFE (predominantly fibrosis):  Prolonged dilatation of any heart chamber will result in diffuse endocardial thickening
  • Gross or histological evidence of a primary cause (congenital, infectious, or inflammatory)
  • Dilated cardiomyopathy of large breed dogs is the most common example
  • May affect entire heart
  • May be focal or multifocal in the atria adjacent to abnormal valves, and is secondary to turbulent blood flow (“jet lesions”)
• Post-infectious myocardial fibrosis
• Feline restrictive cardiomyopathy (left ventricular endocardial fibrosis):  Feline cardiomyopathy with severe endomyocardial fibrosis; fibrosis (may resemble granulation tissue) would extend into myocardium, in contrast to EFE; often associated with heart failure and mural thrombi may be present as well as inflammation in the myocardium; Bartonella infection has been suggested as a cause (Donovan et al., J Comp Pathol. 2018)
• Parvoviral infection (feline panleukopenia virus) is not associated with myocarditis or endomyocardial restrictive cardiomyopathy in cats (McEndaffer et al., Vet Pathol. 2017)
  • Rare intranuclear parvoviral signal via in situ hybridization (ISH) was present in cardiomyocytes in several kittens indicating cardiomyocyte infection is possible, but the infection was not associated with inflammation 

 

COMPARATIVE PATHOLOGY:

• EFE has been reported in dogs, horses, cattle, sheep, pigs, and chickens, but primary EFE has only been confirmed in domestic cats and a few dogs; other reports are likely secondary EFE
• Rare case reports in wild felids (two related tiger cubs, a Pallas cat, and a European wildcat (Gudenschwager et al., J Vet Diagn Invest. 2019)
• Humans: Fibroelastic thickening usually affecting the left ventricular endocardium occurs in patients less than 2 years of age
  • Concomitant problems can occur: aortic valve obstruction or other congenital cardiac anomalies
  • May be the sequela of systemic viral infections (e.g., intrauterine exposure to mumps), gene mutations (e.g., tafazzin)      
• Rats with endocardial spindle cell proliferation:
  • Lesions arise in the endocardium and subendocardial tissue
  • Characterized as fibroproliferative, giving rise to terms including endocardial fibromatosis, fibroelastosis, endocardiosis, and endocardial fibromatous proliferation
  • Possible precursors to schwannomas

 

REFERENCES:

1. Barthold SW, Griffey SM, Percy DH. Pathology of Laboratory Rodents and Rabbits. 4th ed. Ames, IA: Blackwell Publishing; 2016:156.
2. Donovan TA, Balakrishnan N, Carvalho Barbosa I, et al. Bartonella spp. as a possible cause or cofactor of feline endomyocarditis-left ventricular endocardial fibrosis complex. J Comp Pathol. 2018;162:29-42.
3. Gal A, Castillo-Alcala F. Cardiovascular System, Pericardial Cavity, and Lymphatic Vessels. Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:666, 673.
4. 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.
5. Robinson WF, Robinson NA. Cardiovascular system. In: Maxie MG, ed. Jubb, Kennedy, and Palmer’s Pathology of Domestic Animals. Vol 3. 6th ed. St. Louis, MO: Elsevier; 2016:22.
6. Mitchell RN, Andrew AJ. The Heart. In: Kumar V, Abbas AK, Fausto N, Aster J, eds. Robbins and Cotran Pathologic Basis of Disease. 10th ed. Philadelphia, PA: Elsevier; 2021:541, 547.
7. Gudenschwager EK, Abbott JA, LeRoith T. Dilated cardiomyopathy with endocardial fibroelastosis in a juvenile Pallas cat. J Vet Diagn Invest. 2019; 31(2):289-293.

 

 

 

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