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Pythium Insidiosum Keratitis: Histopathology and Rapid Novel Diagnostic Staining Technique
Ruchi Mittal1, Shipra K Jena, Alisha Desai
1*Dalmia Ophthalmic Pathology Services, L. V. Prasad Eye Institute, Bhubaneswar, India; †Tej Kohli Cornea Institute, L. V. Prasad Eye Institute, Bhubaneswar, India; and ‡Department of Pathology, Kalinga Hospital Limited, Bhubaneswar, India.
Purpose:
To elucidate the histopathology of Pythium insidiosum keratitis and to describe a novel, simple, and rapid staining technique for identification of oomycete Pythium insidiosum and to differentiate it from fungi.
Methods:
This is a laboratory investigation study of 38 nonconsecutive cases (37 ocular samples and 1 colonic biopsy); 14 microbiologically diagnosed as Pythium insidiosum keratitis and 24 as fungal keratitis. Review of clinical, demographic details, microbiological results, and identification of cases that necessitated evisceration was performed. Reevaluation of histopathology slides was done using stains such as hematoxylin-eosin, Gomori methenamine silver (GMS), periodic acid-Schiff (PAS), potassium iodide-sulfuric acid (IKI-H2SO4). Morphology, degree, and nature of inflammation and load, distribution, and staining results of Pythium insidiosum and its comparison with fungi were studied.
Results:
Delay in zoospore formation, failure of growth, and delay in identification of Pythium were the main cause of evisceration. Corneal pythiosis showed epithelial ulceration, stromal destruction, and varying inflammation; load and distribution of Pythium were inversely proportional to inflammation. The filaments were commonly wide, with admixed narrower structures and uncommonly involved Descemet membrane. The oomycete was not discretely discerned with PAS stain and stained distinctly with GMS stain and IKI-H2SO4 stain (100% sensitive). In comparison, fungal organisms stained well with PAS and GMS stain, but not with IKI-H2SO4 stain (100% specific).
Conclusions:
Pythium insidiosum keratitis is perhaps not more devastating than fungal keratitis but late diagnosis, misdiagnosis, and treatment as fungal infection are major heralds. Early diagnosis may markedly improve the patient outcome. IKI-H2SO4 is a cost-effective, simple, sensitive, and specific stain for the diagnosis of oomycete Pythium.
Insights
Delayed diagnosis of Pythium insidiosum keratitis leads to poor outcomes. A new stain, potassium iodide-sulfuric acid (IKI-H2SO4), effectively identifies Pythium insidiosum, differentiating it from fungal keratitis.
Area of Science:
- Ophthalmology
- Mycology
- Infectious Diseases
Background:
- Pythium insidiosum keratitis presents diagnostic challenges, often being misdiagnosed as fungal keratitis.
- Oomycete infections require distinct diagnostic approaches compared to fungal infections.
Purpose of the Study:
- To detail the histopathology of Pythium insidiosum keratitis.
- To introduce a novel, rapid staining method for identifying Pythium insidiosum and distinguishing it from fungi.
Main Methods:
- Histopathological analysis of 38 cases (37 ocular, 1 colonic) diagnosed with Pythium insidiosum or fungal keratitis.
- Evaluation of stains including Hematoxylin-Eosin, Gomori Methenamine Silver (GMS), Periodic Acid-Schiff (PAS), and Potassium Iodide-Sulfuric Acid (IKI-H2SO4).
- Comparison of Pythium insidiosum morphology, inflammation, and staining characteristics against fungal keratitis.
Main Results:
- Pythium insidiosum keratitis exhibited epithelial ulceration, stromal destruction, and variable inflammation.
- Pythium insidiosum stained distinctly with GMS and IKI-H2SO4 (100% sensitive), while fungi stained with PAS and GMS (100% specific).
- IKI-H2SO4 demonstrated 100% sensitivity for Pythium insidiosum, whereas PAS and GMS were 100% specific for fungi.
Conclusions:
- Late diagnosis and misdiagnosis of Pythium insidiosum keratitis contribute to poor patient outcomes.
- The IKI-H2SO4 stain is a simple, cost-effective, sensitive, and specific tool for diagnosing Pythium insidiosum.
- Early and accurate diagnosis is crucial for improving outcomes in Pythium insidiosum keratitis.
