JPC SYSTEMIC PATHOLOGY
SPECIAL SENSES SYSTEM
Signalment (JPC Accession # 1372926): German shepherd dog
HISTORY: Tissue from a German shepherd military working dog.
HISTOPATHOLOGIC DESCRIPTION: Eye, cornea: Focally, the superficial third of the corneal stroma is expanded up to 300 µm by moderate numbers of plasma cells, lymphocytes and macrophages, multiple variably-sized vessels lined by hypertrophic endothelial cells (vascularization) and reactive fibroblasts (granulation tissue) and increased clear space (edema). Few aggregates of macrophages within the stroma contain brown to black, granular to globular pigment (melanin/melanosis). There are multifocal areas of corneal epithelial erosion with sloughing of epithelium, as well as areas of mild hyperplasia characterized by thickening up to 50 µm wide by hyperplastic epithelial cells, up to 10 layers thick, with few aggregates of interepithelial neutrophils and macrophages (abscesses). Multifocally, epithelial cells are swollen with pale eosinophilic cytoplasm and occasional intracytoplasmic vacuoles (hydropic degeneration). The epithelium is heavily pigmented with high numbers of melanocytes in the epithelium.
MORPHOLOGIC DIAGNOSIS: Eye, cornea: Keratitis, lymphoplasmacytic and histiocytic, chronic, multifocal, moderate, with epithelial abscesses, stromal and epithelial pigment, vascularization and focal erosion (pannus), German shepherd dog, canine.
CONDITION: Pannus keratitis
SYNONYMS: Chronic superficial keratitis (CSK); German shepherd pannus; Uberreiter's syndrome; superficial stromal keratitis
- Progressive, bilateral, inflammatory and potentially blinding disease of the canine cornea
- Most common in German shepherd dogs (GSD), but may occur in any breed
- Factors implicated in initiation and potentiation of disease include age, breed, gender and environmental factors (e.g. sunlight exposure at high altitudes)
- As with many immune mediated diseases, the predominant cell type in affected corneas is the CD4+ lymphocyte, which secrete IFN-gamma
- There may be aberrant expression of MHC class II within affected corneas which perpetuates the syndrome
- The cornea possesses tissue specific antigens that may be modified by external factors; UV light may alter antigenicity of susceptible cornea leading to cell-mediated inflammation
TYPICAL CLINICAL FINDINGS:
- Age of onset, breed and geographic location (altitude) have prognostic value
- GSDs are typically affected at a young age (1-5 years); the condition is rapidly progressive and severe
- In animals initially affected later in life (4-6 years), lesions are less severe and progress more slowly
- Red, vascularized, conjunctival lesion that begins at the temporal limbus and progresses centrally to form a subepithelial bed of granulation tissue
TYPICAL GROSS FINDINGS:
- Bilateral fibrovascular plaque that is often pigmented, with distinct border surrounded by translucent halo consisting of invading cells and corneal edema
- Third eyelid margin may or may not be thickened and depigmented
TYPICAL LIGHT MICROSCOPIC FINDINGS:
- Superficial corneal vascularization with infiltration of granulation tissue, lymphocytes and plasma cells into superficial corneal stroma
- Interface lymphoplasmacytic inflammation
- Migration of pigment-laden cells commonly accompanies the fibrovascular inflammatory infiltrate (corneal pigmentation)
- Corneal epithelium generally remains intact but may show increased mitotic activity
- Epithelial cell apoptosis
ADDITIONAL DIAGNOSTIC TESTS:
- Signalment, clinical appearance, and response to local immunosuppression are usually sufficient for diagnosis
- Pigmentary keratitis due to chronic irritation (exophthalmic breeds)
- Corneal granulation tissue (healing wounds)
- Keratoconjunctivitis sicca (xerophthalmia) – inadequate tear production > cornea epithelium keratinizes and thickens > rete peg formation (epidermalization); in chronic cases there is corneal ulceration and deep corneal vascularization
- Ulcerative keratitis caused by physical or chemical trauma, desiccation or infection
- Superficial punctate keratitis (noninflammatory): Characterized by non-inflammatory, epithelial and sub-epithelial infiltrates within the cornea
- Nonulcerative deep stromal keratitis Extension from anterior uveitis or endothelial damage (uveal inflammation, trauma, glaucoma)
- Herpetic keratitis: Corneal erosions and ulcers and conjunctivitis; feline herpesvirus-1
- Feline eosinophilic keratitis: Superficial stromal keratitis; numerous eosinophils on scrapings but fewer on histology
- Horses: Mycotic keratitis - deep ulcerative keratitis; Aspergillus or Penicillium sp. most common
- Cattle: Infectious bovine keratoconjunctivitis - conjunctivitis and ulcerative keratitis caused by Moraxella bovis, Moraxella bovoculi and other agents
- Sheep and goats: Infectious keratoconjunctivitis - conjunctivitis and keratitis; many possible etiologies (mycoplasmas, chlamydiae, rickettsiae)
- Andrew SE. Immune-mediated canine and feline keratitis. Vet Clin North Am Small Anim Pract. 2008; 38(2):269-290.
- Dubielzig RR, Ketring KL, McLellan GJ, Albert DM. The principles and practice of ocular pathology. In: Dubielzig RR, Ketring KL, McLellan GJ, Albert DM, eds. Veterinary Ocular Pathology: a comparative review. Philadelphia, PA: Saunders Elsevier; 2010:2.
- Dubielzig RR, Ketring KL, McLellan GJ, Albert DM. Diseases of the cornea and sclera. In: Dubielzig RR, Ketring KL, McLellan GJ, Albert DM, eds. Veterinary Ocular Pathology: a comparative review. Philadelphia, PA: Saunders Elsevier; 2010:212-215.
- Labelle P. The eye. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 6th ed. St. Louis, MO: Mosby Elsevier; 2017:1314.
- Wilcock BP. Special senses. In: Maxie MG, ed. Jubb, Kennedy and Palmer’s Pathology of Domestic Animals. Vol 1. 6th ed. Philadelphia, PA: Saunders Elsevier; 2016:438.
- Williams DL. Histological and immunohistochemical evaluation of canine chronic superficial keratitis. Res Vet Sci. 1999;67(2):191-195.
- Williams DL. Major histocompatibility class II expression in the normal canine cornea and in canine chronic superficial keratitis. Vet Ophthalmol. 2005;8(6):395-400.