Evaluation of the Role of Fluorescence Microscope as a Potential Diagnostic Tool in the Diagnosis of Onychomycosis

Abstract

SUMMARY O nychomycosis is a common persistent infection of the nail unit by fungi either dermatophytes, yeasts or non dermatophyte moulds (NDMs). Onychomycosis is not just a simple cosmetic problem it has a negative effect on the quality of life of those suffering from it and it is a challenging problem to both the patient and the physician. Thought the confirmation of the diagnosis of onychomycosis is difficult but definitive diagnosis is important before commencing management due to the potential risk of therapy; currently, definitive diagnosis is based on culture or direct microscopy. Fungal culture is a time consuming procedure requiring facilities that are not usually available in a dermatopathology laboratory, while KOH preparations have been reported to have 5-15% of false-negative results. Fluorescence microscope with fluorescent stains like acridine orange can be used for diagnosis of onychomycosis and gains higher sensitivity, when compared with the direct microscopic examination using KOH preparation. Our aim in the study was to evaluate the diagnostic utility of fluorescence microscopy in the detection of fungal organisms in nail specimens with clinically suspected onychomycosis using acridine orange stain and H&E stain. We performed our study on 35 patients with clinically suspected onychomycosis of finger and/or toenail each nail sample from every patient subjected to examination by fluorescence microscope using acridine orange stain and H&E stain. Also mycological culture, KOH 20%, H&E stained specimens’ examination under light microscopy were done. The fungal isolates in the study were 65% yeast infection, mainly candida species Followed by non dermatophyte mould infection detected in 32.5% of patients and dermatophyte infection detected in 12.5% of patients. The predominant clinical type of onychomycosis in the study was distal-lateral subungual onychomycosis (74%) followed by total dystrophic onychomycosis (14%) and the least common was proximal subungual onychomycosis (12%). Mycological examination with KOH 20%and examination of hematoxylin and eosin stained sections under light microscopy reveled 32 cases (91%) positive for fungal infection which were confirmed by mycological cultures with different media to detect yeast, dermatophytes and non dermatophyte moulds. Examination under fluorescence microscopy with acridine orange stain (by the blue filter and lens power x40) revealed strong fluorescence in all positive cases (32 cases), it could detect all types of fungal elements and it had high credibility in detecting the positive fungal infections. Our study is limited in calculating the sensitivity of fluorescence microscopy with acridine orange stain due to absence of false-negative results yielded by culture, KOH 20% direct microscopic examination and fluorescence microscopy using acridine orange stain. Also the specificity couldn’t be calculated since these tests would not be used to screen clinically normal nails for onychomycosis. Furthermore false-positive results for the acridine orange stained specimens were not detected because of its specific criteria for visualizing the fungal elements