Fungal Fluorescence in Hematoxylin-Eosin Stained Sections

A forty-six-year-old male presented to our dermatology clinic with two-year history of itching on his groin. His medical history revealed various topical corticosteroid creams without improvement of the skin lesion. Dermatological examination revealed erythematous nodules and follicular pustules on erythematous background on the inguinal area (Figure 1a). Potassium hydroxide (KOH) examination was negative. Tzanck smear revealed abundant neutrophils without bacteria, fungi, or parasite. The histopathological examination showed granuloma formation with multinuclear giant cells and Periodic acid-Schiff (PAS)-positive hyphae and spores around the hair follicles (Figure 1b, 1c). Hematoxylin-eosin (H&E)-stained slides were examined under an immunofluorescence microscope, and these hyphae and spores showed autofluorescence (Figure 1d). Based on the clinical and histopathological findings, a Majocchi’s granuloma was considered. All lesions disappeared with topical and systemic terbinafine (250 mg/day) treatment for six weeks. Pearls; Clinical: Not only bacteria, but also fungi, parasites, and viruses may cause folliculitis. Cytology should be initially done to identify the causes of infectious folliculitis. In case of negative cytology, histopathological examination and molecular methods can be used. Cytological: To cytologically identify all of the causes of folliculitis, four separate samples should be taken: (i) the first sample is stained with May-Grünwald-Giemsa for routine cytological examination; (ii) the second sample is used for KOH testing; (iii) the third sample is stained with an acid-fast stain to detect mycobacteria; and (iv) the last specimen is Gram-stained to identify whether it is Gram-positive or Gram-negative (1). Histopathological: In infectious diseases, a definitive diagnosis should be done to identify the etiologic agent. The detection of fungal elements is challenging, when histopathological examination is performed with the H&E staining. However, PAS and Gomori’s Methenamine Silver staining can facilitate the detection of fungal spores, hyphae, and arthrospores within the hairs, hair follicles, and in the dermal infiltrates. In addition, autofluorescence can be detected, when H&E stained slides are examined under a fluorescent microscope (2).