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Phlyctenular Keratitis
Cornea
1. Clinical Analogy & Conceptual Overview
The Clinical Analogy: 'The Eye as a Battlefield of Hypersensitivity'
Imagine your immune system as an army that is on high alert. In phlyctenular disease, a foreign antigen (usually tuberculoprotein or staphylococcal exotoxin) arrives at the ocular surface - like a foreign spy entering a military camp. The immune army (sensitized T-lymphocytes) does not just expel the spy; it launches a full ground assault - resulting in focal necrotizing granuloma formation at the limbus or cornea. The 'phlycten' is the battle scar: a nodular collection of lymphocytes, macrophages, and plasma cells at the site of antigen encounter. The tragedy is that the immune response is protective in intent but destructive in execution - a classic Type IV delayed hypersensitivity.
Definition
- Phlyctenular keratoconjunctivitis is a nodular, non-infectious, delayed hypersensitivity (Type IV) reaction of the conjunctiva and/or cornea to microbial antigens.
- Classically, this is associated with mycobacterial antigens in tuberculosis-endemic settings or Staphylococcus aureus antigens, especially with blepharitis, in high-income settings.
- It manifests as one or more pale, raised, circumscribed nodules (phlyctens) at the limbus, bulbar conjunctiva, or cornea.
Exam pearl
- The term 'phlycten' derives from the Greek phlyktaina (= blister/pustule), although true vesiculation is not a feature - the lesion is a necrotizing inflammatory nodule that may develop central ulceration; epithelioid granulomas with caseous necrosis are specifically described in tuberculous conjunctival disease rather than as a universal feature of phlyctens.
2. Epidemiology & Risk Factors
| Parameter | Detail |
|---|---|
| Age | • Predominantly seen in children • Can occur at any age |
| Sex | • Slight female preponderance in some series |
| Geography | • Common in developing countries (tuberculosis-endemic) • Staphylococcal type in West |
| Laterality | • Usually unilateral • Bilateral disease can occur |
| Season | • Spring seasonal peak reported |
| Recurrence | • HIGH - hallmark of the disease • Each recurrence risks corneal scarring |
| Nutrition | • Malnutrition and Vitamin A deficiency have been reported as historical associations • May contribute to delayed recovery |
| Socioeconomic | • Overcrowding can increase tuberculosis exposure • Poor hygiene and overcrowding are not specific established risk factors for tuberculosis-related type |
| Associated conditions | • Active tuberculosis • Latent tuberculosis infection • Relative frequency varies by setting • Staphylococcal blepharitis • Rosacea • Molluscum contagiosum • Coccidioidomycosis • Chlamydia |
| Parameter | Detail |
|---|---|
| Age | • Predominantly seen in children • Can occur at any age |
| Sex | • Slight female preponderance in some series |
| Geography | • Common in developing countries (tuberculosis-endemic) • Staphylococcal type in West |
| Laterality | • Usually unilateral • Bilateral disease can occur |
| Season | • Spring seasonal peak reported |
| Recurrence | • HIGH - hallmark of the disease • Each recurrence risks corneal scarring |
| Nutrition | • Malnutrition and Vitamin A deficiency have been reported as historical associations • May contribute to delayed recovery |
| Socioeconomic | • Overcrowding can increase tuberculosis exposure • Poor hygiene and overcrowding are not specific established risk factors for tuberculosis-related type |
| Associated conditions | • Active tuberculosis • Latent tuberculosis infection • Relative frequency varies by setting • Staphylococcal blepharitis • Rosacea • Molluscum contagiosum • Coccidioidomycosis • Chlamydia |
EXAM PEARL - Historical Shift in Aetiology
- In the pre-antibiotic era, phlyctenular disease was commonly attributed to tuberculin hypersensitivity in settings with high tuberculosis prevalence.
- Today in developed nations, tuberculosis has been supplanted by staphylococcal infection and worm infestation as etiological associations.
- In India, tuberculosis remains a major association of phlyctenular eye disease.
- A positive Mantoux test does not confirm active tuberculosis; it requires clinical evaluation and further testing to distinguish tuberculosis infection from tuberculosis disease.
- A positive Mantoux test may also reflect Bacille Calmette–Guérin vaccination or exposure to nontuberculous mycobacteria.
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Keep reading Phlyctenular Keratitis
12 more sections are included with the Clinical plan.
- Pathophysiology & Immunology
- Classification
- Clinical Features - Conjunctival Phlycten
- Clinical Features - Corneal Phlycten
- Differential Diagnosis & Comparison Tables
- Investigations