Local expression and systemic release of stem cell factor in systemic sclerosis with diffuse hyperpigmentation

Sir, Systemic sclerosis (SSc), a connective tissue disease characterized by tissue fibrosis with excessive collagen deposition in the dermis or various internal organs, is of unknown pathogenesis. Histological examination reveals perivascular inflammatory infiltrates including macrophages, T lymphocytes or mast cells, in the early phase of scleroderma skin.1 We have observed that scleroderma patients often present with diffuse pigmentation as the disease progresses, associated with itching. The mechanism of the increased pigmentation and itching has not been elucidated. Recent investigation has shown that there is no evidence of adrenal deficiency in scleroderma patients.2 An increased number of mast cells is present in lesional skin of patients with oedematous phase scleroderma.3,4 Mast cells release a number of cytokines involved in the promotion of dermal sclerosis. We have recently observed that stem cell factor (SCF), a growth factor for mast cells, is strongly expressed on various types of cells including fibroblasts, endothelial cells, keratinocytes and mast cells in lesional skin of SSc.5 Recently, SCF expression in SSc has also been reported to be enhanced in the oedematous phase, whereas serum SCF level is elevated in the sclerotic phase.6 SCF also stimulates melanin production by melanocytes.7 We therefore assessed the serum level of SCF at several time points in a typical case of SSc showing diffuse hyperpigmentation in parallel with the disease progression.