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Phlyctenular Keratoconjunctivitis and Marginal Staphylococcal Keratitis


Key Concepts

  • Phlyctenular keratoconjunctivitis (PKC) and staphylococcal marginal keratitis are both hypersensitivity reactions to a microbial antigen.

  • PKC is most likely a type IV hypersensitivity reaction (cell mediated) that causes nodular lesions on the conjunctiva and cornea.

  • Staphylococcal marginal keratitis is most likely a type III hypersensitivity reaction (immune complex) that causes peripheral corneal infiltrates separated from the limbus by a clear zone.

  • External inocula (bacterial proteins) to the ocular surface are needed to “trigger” the condition in a sensitized individual.

  • The mainstays of therapy include treating acute inflammation with topical corticosteroids and decreasing the load of bacterial antigens with topical antibiotics and lid hygiene to minimize recurrences.

Acknowledgments

The author and editors recognize the work of Reza M. Mozayeni and Sheridan Lam for their contributions from the original chapter.

Phlyctenular keratoconjunctivitis (PKC) and marginal staphylococcal keratitis are noninfectious inflammatory processes of the ocular surface. Although clinically distinct entities, these two conditions share a common pathophysiologic mechanism: an immune reaction to a microbial antigen. This immune reaction can lead to corneal and conjunctival nodules (PKC) or peripheral corneal infiltrates (marginal staphylococcal keratitis). Both conditions are usually self-limiting. Shared presenting symptoms create diagnostic dilemmas that require clinicians to be able to differentiate these entities from other diagnoses (i.e., acute infections) and avoid inappropriate treatment.

Phlyctenular Keratoconjunctivitis

Background and History

PKC, or phlyctenulosis, is thought to represent a delayed hypersensitivity reaction to a number of antigens, the most common being tuberculoprotein and staphylococcal antigen. The term phlyctenule is derived from the Greek word phlyctena , which means “blister.” This was likely a reference to the appearance of a conjunctival or corneal nodule after undergoing necrosis and ulceration. The earliest description of phlyctenulosis is found in a textbook written by C. de St. Yves in 1722, according to Duke-Elder.

PKC was classically described as a disease of sickly children in areas of endemic tuberculosis. In the 1940s, Sorsby was the first to confirm the strong correlation with tuberculosis when he reported that 85% of patients with PKC tested positive to the tuberculin skin test versus 15% in a control group in the same hospital. Fritz et al. and Philip et al. later made similar observations in studies of impoverished Alaskan villages with high rates of tuberculosis, noting that the prevalence of PKC correlated directly with tuberculin skin sensitivity. There was also increased morbidity in children with PKC, who had greater odds of developing clinical tuberculosis. ,

Etiology and Epidemiology

In countries where tuberculosis is still relatively common, Mycobacterium tuberculosis remains the primary cause of PKC. In the United States and other developed countries that currently have a low incidence of tuberculosis, the most common pathogen associated with this disorder is Staphylococcus. The association of PKC and Staphylococcus was actually reported as early as the 1950s by Thygeson and then characterized further by Ostler and Lanier, who reported five patients with PKC and positive skin tests to Staphylococcus antigens. Other antigens have been implicated as well such as Chlamydia , , Coccidioides , Candida , herpes simplex virus (HSV), and parasites.

In early studies when tuberculosis was endemic, , PKC was described as a condition that occurred most often in the first two decades of life, with a peak incidence in the mid-teens, and rarely occurred before 5 years of age. A higher incidence in females was consistently reported. A peak incidence in the spring and summer has been reported. A review of the more recent reports on PKC in the United States , , , still shows this to be a disease most commonly presenting in the teenage years with a preference towards females.

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