Kerion is an inflammatory form of tinea capitis that appears as crusty nodules covered in bogs. Because so many mycological samples are falsely negative, diagnosing kerion can be difficult.

For a study, researchers sought to determine the prevalence of false-negative mycological samples in children with kerion before antifungal therapy, a retrospective investigation was carried out. At baseline and after the administration of an oral antibiotic course, with or without the administration of an oral steroid course, specimens were taken for direct microscopy and fungal culture. Kerion was classified as either minimally inflammatory when an erythematous, dry scalp nodule was detected or as highly inflammatory when a painful, wet scalp nodule with spontaneous purulent discharge or excessive crust was present.

Twenty-three children, with a mean age of 7.9 ±3.0 years, were enrolled in the research. The most prevalent species that was isolated was Trichophyton tonsurans (69.6%). Before therapy, highly inflammatory kerions were substantially more likely than moderately inflammatory kerions to have a negative culture (80% vs. 16.7%, P< .01). Thirteen non-inflammatory tinea capitis lesions were all culture-positive. Higher frequencies of positive fungal cultures were reported compared to baseline (90.9% vs. 18.2%, P< .01) after an oral antibiotic and steroid course was administered to the majority of highly inflamed kerions (n = 11/13).

Only in the most inflammatory types of kerion were substantial frequencies of negative fungal cultures discovered. After an oral antibiotic and steroid regimen, sampling a highly inflamed kerion increased the likelihood of obtaining positive fungal cultures. Additionally, sampling of non-inflammatory tinea capitis lesions exhibited the maximum culture sensitivity (when present in addition to the kerion).

Reference: onlinelibrary.wiley.com/doi/10.1111/pde.15021