THE ABNORMALITY OF SWEAT DUCT FUNCTION IN PSORIASIS

SUMMARY.— Following complete cellophane tape stripping of the plaques in psoriasis, the sweat rates were significantly greater than the rates in stripped clinically normal skin between the plaques. Na + , K + , urea and lactate concentrations were all considerably reduced in sweat collected from the plaques before stripping. K + and urea concentrations increased after stripping but remained less than the concentrations in the sweat from the clinically normal skin. Lactate concentrations in sweat from the plaques remained low after stripping and the increase in Na + was less than anticipated from the change in sweat rate. These changes are interpreted as a primary defect in sweat duct function in the plaques involving impaired absorption of water and to a lesser extent Na + from the primary secretion produced by the coil. This results in an apparent increase in sweat rate and reduced solute concentrations after stripping. It is concluded that there are two major defects in the sweat glands in psoriasis, (i) sweat duct blockage, (ii) impaired ductal absorption, primarily of water, but also of Na + . There is also a defect in lactate metabolism in the sweat gland, the nature of which has not yet been defined.