Cutaneous PGP 9.5 distribution patterns in hidradenitis suppurativa

The aim of this study was to investigate the presence and density of the nerve fibre-marker protein gene product 9.5 (PGP 9.5), with immunohistochemistry, in skin from patients with hidradenitis suppurativa (HS). Punch biopsies were obtained from 16 patients; 10 with involvement of the groin and six with axillary disease. Specimens were taken from HS lesions in the groin or axilla, clinically non-involved skin and from 12 healthy control subjects. Coded slides were observed in the microscope and PGP 9.5 positive nerve fibre profiles (profiles) as well as PGP 9.5 positive cells (cells) were counted. The overall impression was that the median number of profiles was decreased in lesional epidermis, yet statistically significant only in the groin (p = 0.0014). The median number of profiles in dermis was significantly decreased in lesional skin of the axilla, whereas in the groin there were contradictory findings with significantly increased number of profiles in upper dermis and non-significant in mid and lower dermis. The number of cells with strong immunofluorescence was few or absent in epidermis, but increased in dermis in the lesional skin. This difference was statistically significant throughout the dermis in specimens from the groin (p < 0.01) and showed the same trend, although not significant, in the axilla. The PGP 9.5 immunofluorescent cells were not yet further investigated, so it is not exactly known what cell type they represent. In conclusion, despite several study limitations, the findings indicate that PGP 9.5 positive nerve fibres could be involved in the pathogenesis of HS. Both regarding the profiles and the cells, further studies remain to show if these differences are primary events, or secondary to e g chronic inflammation, which is considered a major issue of HS.