Abstract

Background: Tinea capitis and Majocchi’s granuloma have a wide range of clinical presentations from erythematous papules and perifollicular nodules to subcutaneous nodules or abscesses. Biopsy can be used to distinguish these entities from other conditions with similar cutaneous presentations. Objective: To evaluate the proportion of hairs infected on biopsy of fungal folliculitis. Methods: Tinea capitis and Majocchi’s granuloma biopsies from January 2000 to December 2020 were reviewed by a dermatopathologist to count the total number of hairs on the sample and the total infected. All cuts of the specimen were examined with a conscious effort to only count hairs once. Results: 72 biopsies were included in the study. The median number of hair follicles per biopsy was 3 (IQR 1,4; range 1-54) and the median proportion of hairs infected was 54.2% (IQR 33.3%, 100.0%; range 11.1-100%). Nineteen (26.4%) had only one hair included in the biopsy which was also an infected hair. The percentage of total hair follicles infected differed significantly when comparing biopsies from an extremity versus the scalp (median 66.6% vs. 36.6%, p = 0.0344). The proportion of infected hairs did not differ by sex, race, technique, or stain used. Conclusion: This study demonstrates not all hairs exhibit fungal infection, even in confirmed cases of fungal folliculitis. Our estimate of infected hairs (approximately 54%) is likely an overestimate, given the design of the study. Pathologists should be aware of the limitations of biopsy in diagnosis of fungal folliculitis, particularly in biopsies with few hairs. To minimize false negative results, examination of multiple hairs is essential when considering this diagnosis.

Financial Disclosure:
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