JPC SYSTEMIC PATHOLOGY

INTEGUMENTARY SYSTEM

October 2013

I-M20

 

Signalment (JPC #86N264D):  A 6-year-old Shire gelding

HISTORY:  This horse had a 1-month history of lameness and reluctance to move.

HISTOPATHOLOGIC DESCRIPTION:  Hoof and 3rd phalanx:  Diffusely the lamellar-horn margin is highly irregular and the normal architecture of the hoof wall is obscured by degeneration, necrosis, and marked irregular hyperplasia of the epidermal laminae.  Diffusely, the primary epidermal laminae are markedly elongated and expanded up to four times normal by parakeratotic and orthokeratotic hyperkeratosis and occasionally contain accumulations of lamellated keratin or dyskeratotic keratinocytes.  Secondary epidermal laminae are disorganized, blunted, clubbed, thickened or elongated and occasionally form anastomosing epidermal cords.  Multifocally, there is loss of individual or groups of secondary epidermal laminae.  Remaining epidermal laminar cells are often swollen with abundant pale, microvacuolated cytoplasm (intracellular edema) or separated by clear space (intercellular edema).  In all layers of the epidermis, there are occasional scattered keratinocytes that have intensely eosinophilic cytoplasm and a pyknotic nucleus (necrosis).  Multifocally, there are longitudinal clefts separating the epidermal laminae and basement membrane from the adjacent dermal laminae; clefts rarely contain a small amount of cellular debris and few erythrocytes.    There are increased clear spaces separating fibrous connective tissue in both primary and secondary dermal laminae, and lymphatics within the laminar corium are frequently dilated (edema).  Multifocally, the third phalanx exhibits scalloped margins lined by numerous osteoblasts with moderate numbers of osteoclasts within Howship’s lacunae and thin basophilic reversal lines that roughly parallel the surface (bony remodeling); P3 is multifocally capped by irregular proliferations of woven bone and the medullary cavity is filled with loose, myxomatous fibrous connective tissue.  Caudal to P3 there is a nodular accumulation of degenerate neutrophils, macrophages, hemorrhage, finely fibrillar and beaded eosinophilic material (fibrin), and eosinophilic cellular and karyorrhectic debris (necrosis). 

MORPHOLOGIC DIAGNOSIS:  Hoof and 3rd phalanx:  Epidermal laminar degeneration and necrosis, chronic, diffuse, severe with epidermal hyperplasia, hyperkeratosis, multifocal basement membrane retraction, edema, and bony remodeling of P3, Shire, equine.

CONDITION:  Laminitis

SYNONYM:  Founder

GENERAL DISCUSSION:

PATHOGENESIS: 

TYPICAL CLINICAL FINDINGS:

TYPICAL GROSS FINDINGS: 

TYPICAL LIGHT MICROSCOPIC FINDINGS:

Acute:

Chronic:

ULTRASTRUCTURAL FINDINGS:

ADDITIONAL DIAGNOSTIC TESTS: 

DIFFERENTIAL DIAGNOSIS:

COMPARATIVE PATHOLOGY:

References:

  1. Belknap, JK and Black, SJ. Sepsis-related laminitis.  Equine Vet J.  2012; 44: 738-740.
  2. Belknap JK, Giguere S, Pettigrew A, Cochran AM, Van Eps AW, Pollitt CC. Lamellar pro-inflammatory cytokine expression patterns in laminitis at the developmental stage and at the onset of lameness: Innate vs. adaptive immune response. Equine Vet J 2007; 39:42-47.
  3. Eades SC. Overview of current laminitis research. Vet Clin North Am Equine Pract. 2010; 26(1):51-63.
  4. Engiles JB. Pathology of the distal phalanx in equine laminitis: More than just skin deep. Vet Clin North Am Equine Pract. 2010; 26(1):155-165.
  5. Engiles JB, Galantino-Homer HL, Boston R, McDonald D, Dishowitz M, Hankenson KD. Osteopathology in the equine distal phalanx associated with the development and progression of laminitis. Vet Pathol. 2015;52(5):928-44.
  6. Hargis AM, Ginn PE. The integument. In: McGavin MD, Zachary JF, eds. Pathologic Basis of Veterinary Disease. 5th ed. St. Louis, MO: Mosby Elsevier; 2007; 1238-1239.
  7. Karikoski NP, McGowan CM, Singer ER, Asplin KE, Tulamo RM, Patterson-Kane JC. Pathology of natural cases of equine endocrinopathic laminitis associated with hyperinsulinemia. Vet Pathol. 2015;52(5):945-56.
  8. Langenmayer MC, Gollnick NS, Majzoub-Altweck M, Scharr JC, Schares G, Hermanns W. Naturally acquired bovine besnoitiosis: Histological and immunohistochemical findings in acute, subacute, and chronic disease.  Vet Pathol. 2015;52(3):476-88.
  9. Mauldin EA, Peters-Kennedy J. Integumentary system. In: In: Maxie MG Jubb, Kennedy,and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Elsevier Ltd. 2016:702-703.
  10. Pollitt, CC. Laminitis pathophysiology.  In:  Floyd, Mansmann, eds.  Equine Podiatry. 1st ed.  Louis, MO:  Saunders; 2007:313-319.


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