Ultrasound examination of hair follicles in hidradenitis suppurativa

Objective: To describe the in vivo skin echostructure, hair follicle shape, and dermal thickness in hidradenitis suppurativa. Design: Qualitative and quantitative assessment of high-frequency (20-MHz) B-mode ultrasound images of lesional and paralesional skin. Setting: University hospital. Patients: Age- and sex-matched outpatients with hidradenitis suppurativa (n=15) and healthy control subjects (n=13). Median age was 34 years (range, 31-38). Results: Clinically normal paralesional hair follicles in hidradenitis have an abnormal shape. The follicles appear to be wider in the deep dermis, the difference being statistically significant in the genitofemoral region (P=.007). Patients with hidradenitis have larger follicles in the axilla than controls (P=.002). Mature acne and hidradenitis lesions are indistinguishable, but both are different from epidermal cysts. Mean axillary and genitofemoral skin was significantly thicker in patients than in controls. Conclusions: In vivo ultrasonography shows characteristic differences in the shape of hair follicles in hidradenitis. The general underlying abnormalities appear to occur in the deep part of the follicle. The mature lesions are indistinguishable from acne, but are clearly different from epidermal cysts. A thickened skin may play pathogenic role in the development of hidradenitis.