What is the pathophysiology of peripheral ulcerative keratitis (PUK)?

Updated: Jun 11, 2019
  • Author: Ellen N Yu-Keh, MD; Chief Editor: Andrew A Dahl, MD, FACS  more...
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Answer

The peripheral cornea has distinct morphologic and immunologic characteristics that predispose it to inflammatory reactions. Unlike the avascular central cornea, the peripheral cornea is closer to limbal conjunctiva and derives part of its nutrient supply from the limbal capillary arcade, a source of immunocompetent cells, for example, macrophages, Langerhans cells, lymphocytes, and plasma cells. [2, 3] Any inflammatory stimulus in the peripheral cornea that is caused by invasion of microbial organisms (bacteria, virus, fungi, and parasites), immune complex deposition (in systemic immune diseases), trauma, malignancy, or dermatologic conditions may produce local and systemic immune responses, resulting in neutrophil recruitment and complement activation (both classic and alternative pathways) in both tissue and vessels. [2]

Activated complement components can increase vascular permeability and further generate chemotactic factors for neutrophils (eg, C3a, C5a). Neutrophils, in turn, infiltrate the peripheral cornea and release proteolytic and collagenolytic enzymes, reactive oxygen metabolites, and proinflammatory substances (eg, platelet-activating factor, leukotrienes, prostaglandins), causing dissolution and degradation of the corneal stroma. [4, 5] In addition, the inflamed limbal conjunctiva itself is capable of producing collagenase, which contributes to stromal degradation. [6]

Systemic diseases that may cause immune complex deposition at the peripheral cornea and PUK include such collagen vascular diseases as rheumatoid arthritis (RA), granulomatosis with polyangiitis (GPA; previously known as Wegener granulomatosis), polyarteritis nodosa (PAN), relapsing polychondritis (RP), and systemic lupus erythematosus (SLE). Infectious conditions, whether systemic (eg, hepatitis, syphilis) or local (eg, herpes simplex keratitis, fungal keratitis), and noninfectious local disorders (eg, Mooren ulcer, marginal keratitis) may also cause PUK.

In summary, the major pathophysiologic mechanism of PUK is a result of degradation and tissue necrosis of corneal stroma produced by degradative enzymes, which are released primarily by neutrophils attracted into the area by diverse stimuli.


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