Increased mast cell numbers in the sclerotic skin of porphyria cutanea tarda.

We quantitated numbers of mast cells in the sclerotic skin noted on the dorsa of the hands of 10 patients with porphyria cutanea tarda (PCT), and compared them with those of diffuse scleroderma and healthy controls. Mast cell counts in sclerodermoid skin of PCT patients were significantly greater than those in involved skin of 9 patients with diffuse scleroderma in its late stage and also greater than those in normal skin of 8 controls. When mast cell density was analyzed according to the depth of the dermis, an 84% increase was noted in the uppermost layer (0-0.2 mm in depth) and a 150% increase in the second uppermost layer (0.2-0.4 mm in depth) in the patients with PCT when compared with those in the corresponding sites of the controls. These results suggest a possible role of mast cells in the pathogenesis of sclerodermoid skin of PCT.