Elevated plasma histamine levels in systemic sclerosis (scleroderma).

Systemic sclerosis is characterized by excessive deposition of collagen and other matrix proteins in the skin and internal organs. One hypothesis supports fibroblast stimulation for production of excess amounts of collagen by factors present in the blood or released by cells composing inflammatory tissue infiltrates. Increased numbers of mast cells are present in the involved skin of patients with systemic sclerosis, and histamine has been thought to be a possible mediator of fibrosis in this and other fibrotic conditions. We therefore measured plasma histamine levels in 32 patients with systemic sclerosis and found elevated levels in 18 patients (56%). Elevated plasma histamine levels were more common in patients with diffuse disease (74%), in contrast to limited disease (31%). The degree of clinical activity and the duration of disease could not be correlated with histamine levels.