Objective: Systemic sclerosis (SSc) is characterized by skin sclerosis, which develops from the distal extremities and spread to the trunk. However, several reports implied the involvement of mast cells in SSc based on examination of forearm skin specimens, but that there no studies that examined digital skin specimens.

Methods: Skin biopsies were obtained from the distal one-third of the forearm and between distal and proximal interphalangeal joints from 46 SSc patients, as well as from 29 non-SSc patients and normal controls. Dermal mast cells were detected histologically using NanoZoomer Digital Pathology.

Results: Dermal mast cells density was significantly higher in both the forearms and fingers in SSc patients compared to non-SSc and normals. Digital dermal mast cell density was significantly higher in patients with diffuse cutaneous SSc than in local cutaneous SSc patients and also in the anti-topoisomerase I antibody-positive group than in the -negative group, though such tendency was not noted in the forearm dermis. Furthermore, digital dermal mast cell density correlated significantly with Rodnan’s Skin Thickness Score, which reflects systemic skin sclerosis.

Conclusion: Digital accumulation of toluidine blue- and/or c-kit-positive dermal mast cells appears to be involved in the early stages of the pathological processes of SSc, especially in patients positive for anti-topoisomerase I antibody.