JPC SYSTEMIC PATHOLOGY

SPECIAL SENSES SYSTEM

April 2024

S-M09

 

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 as well as multiple variably-sized vessels lined by hypertrophic endothelial cells (vascularization), reactive fibroblasts oriented perpendicularly to small caliber vessels (granulation tissue), and increased clear space (edema). Throughout the less affected corneal stroma, there is loss of clefting (edema). Within the superficial stroma there are few small aggregates of macrophages that contain brown to black, granular to globular pigment (melanin). The corneal epithelium multifocally exhibits: erosion with sloughing of epithelial cells, mild hyperplasia with cells piling up to 10 cell layers thick, hydropic degeneration in which epithelial cells are swollen with pale eosinophilic cytoplasm and occasionally contain intracytoplasmic vacuoles, few small intraepithelial abscesses with aggregates of interepithelial neutrophils and macrophages, and heavy melanin pigmentation (hyperpigmentation). 

 

MORPHOLOGIC DIAGNOSIS: Eye, cornea: Keratitis, lymphoplasmacytic and histiocytic, chronic, multifocal, moderate, with epithelial abscesses, stromal and epithelial hyperpigmentation, vascularization, and focal corneal erosion (pannus), German shepherd dog, canine.

 

CONDITION: Pannus keratitis

 

SYNONYMS: Chronic superficial keratitis (CSK); German shepherd pannus; Uberreiter's syndrome; superficial stromal keratitis

 

GENERAL DISCUSSION: 

• Progressive, bilateral, inflammatory, 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)

 

PATHOGENESIS:

• 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 

 

TYPICAL CLINICAL FINDINGS:

• 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

 

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:  

 

DIFFERENTIAL DIAGNOSIS:

For keratitis:

• 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)

 

COMPARATIVE PATHOLOGY:

Common causes of keratitis in other species:

• Cats:  

• 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 sp. 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)

 

References:

1. Labelle P. The Eye. In: Zachary JF, ed. Pathologic Basis of Veterinary Disease. 7th ed. St. Louis, MO: Elsevier; 2022:1428.
2. 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.

 

 

 

 

 

 

 

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