Mammary Hidradenitis Suppurativa Lesions - A Suggestion for Phenotyping.

Background: Hidradenitis suppurativa (HS) is an under-diagnosed chronic inflammatory skin disease of the pilosebaceous unit of apocrine gland-rich parts of the body. The mammary area is the fourth most HS-affected area and, as typical lesions include non-fluctuating nodules, abscesses, and tunnels/sinus tracts, mammary HS is often mistaken for other mammary "boils", such as sub-areolar and granulomatous non-lactating breast abscesses. Our objective was to present a spectrum of mammary HS lesions, explore a possible classification, and expose mammary HS as a possible differential diagnosis to non-lactational breast abscesses.

Methods: A cross-sectional study on current and newly-referred patients treated for HS affecting the mammary area. Anamnestic information, subjective outcome measures, and lesion counts including anatomical location were collected. Patients with similar morphologies were grouped, and characteristics for the groups were investigated.

Limitations: We were not aware of the number of morphologies we would find, and as a result the study did not have sufficient power to show significant differences after correction for multiple testing.

Results: We found three morphologically different subtypes of mammary HS; the Sternal, the Frictional, and the Nodule types. These groups differed in anatomical lesion characteristics and other patient characteristics. Furthermore, we found a fourth Mixed type - a combination of the other three.

Conclusion: Differential diagnosis between mammary HS and sub-areolar or granulomatous non-fluctuating non-lactating breast abscess is most easily performed by assessing the precise anatomical location of the lesion and determining if the mammary lesion is the only lesion present or if similar lesions exist in other HS-specific areas.