Melanin pigmentation of the skin in primary biliary cirrhosis

A histological and ultrastructural study has demonstrated that cutaneous pigmentation in primary biliary cirrhosis (PBC) is due to the presence of increased amounts of melanin, widely dispersed throughout both epidermis and dermis. No deposits of stainable iron were observed. Compared with skin from matched sites from control patients with alcoholic cirrhosis and no pigmentation, the melanocyte: keratinocyte ratio was not significantly higher in PBC. However, in PBC, melanosomes persisted to unusually high levels in the epidermis and were packaged in larger membrane-bound clusters than was the case in the controls. Whether excess melanin results from increased melanogenesis or defective melanin degradation remains unclear, although there is some evidence favouring the latter mechanism. No hormonal (beta-MSH and ACTH) or chemical (bile salt irritation) stimuli to increase melanogenesis were demonstrated.