JPC SYSTEMIC PATHOLOGY
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 250 um (20x normal) by numerous fibrocytes, fewer fibroblasts, and many layers of collagen and elastic fibers. Superficially, fibers are thin, loosely and randomly arranged, and separated by increased clear space and myxomatous material. Fibers within the deeper layers are thicker, more tightly packed, and are parallel. Multifocally the 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)
- Rare, congenital, inherited disease that primarily affects Burmese and Siamese cats leading to early onset of congestive heart failure (CHF) and death
- Diffuse endocardial thickening without other significant cardiac lesions
- 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
- 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:
- Masson’s trichrome for collagen; Verhoeff-Van Gieson or Movat for elastic fibers
- Secondary EFE (predominantly fibrosis): Results from 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
- Endocardial fibroelastosis has been reported in dogs, horses, cattle, sheep, pigs, and chickens (only in domestic cats and a few dogs has primary EFE been confirmed; other reports are often likely secondary EFE)
- Rare case reports in wild felids (two related tiger cubs, a Pallas cat, and a European wildcat)
- Cushing TL. Endocardial fibroelastosis in a quarterhorse mare. J Comp Pathol. 2013;149(2-3):318-321.
- Donovan TA, Balakrishnan N, et al. Bartonella as a possible cause or cofactor of feline endomyocarditis-left ventricular endocardial fibrosis complex. J Comp Path. 2018;162:29-42.
- Kimura Y, Karakama S, 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, Gal A. Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Elsevier; 2017:595.
- 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, 30.
- Schoen FJ, Mitchell RN. The heart. In: Kumar V, Abbas AK, Fausto N, Aster J, eds. Robbins and Cotran Pathologic Basis of Disease. 9th ed. St. Louis, MO: Elsevier; 2015:570.
- 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.