High accuracy of recognition of common forms of folliculitis by dermoscopy: An observational study.

Background: Clinical differentiation of folliculitis types is challenging. Dermoscopy supports the recognition of folliculitis etiology, but its diagnostic accuracy is not known.

Objective: To assess the diagnostic accuracy of dermoscopy for folliculitis.

Methods: This observational study included patients (N = 240) with folliculitis determined on the basis of clinical and dermoscopic assessments. A dermoscopic image of the most representative lesion was acquired for each patient. Etiology was determined on the basis of cytologic examination, culture, histologic examination, or manual hair removal (when ingrowing hair was detected) by dermatologist A. Dermoscopic images were evaluated according to predefined diagnostic criteria by dermatologist B, who was blinded to the clinical findings. Dermoscopic and definitive diagnoses were compared by dermatologist C.

Results: Of the 240 folliculitis lesions examined, 90% were infections and 10% were noninfectious. Infectious folliculitis was caused by parasites (n = 71), fungi (n = 81), bacteria (n = 57), or 7 viruses (n = 7). Noninfectious folliculitis included pseudofolliculitis (n = 14), folliculitis decalvans (n = 7), and eosinophilic folliculitis (n = 3). The overall accuracy of dermoscopy was 73.7%. Dermoscopy showed good diagnostic accuracy for Demodex (88.1%), scabietic (89.7%), and dermatophytic folliculitis (100%), as well as for pseudofolliculitis (92.8%).

Limitations: The diagnostic value of dermoscopy was calculated only for common folliculitis. Diagnostic reliability could not be calculated.

Conclusion: Dermoscopy is a useful tool for assisting in the diagnosis of some forms of folliculitis.