Cutaneous mononuclear cells and eosinophils are significantly increased after warm water challenge in pruritic areas of polycythemia vera.

Background: Increased cutaneous cells following warm water challenge in pruritus-related polycythemia vera (PV) have been reported, but their nature and magnitude are not known.

Methods: Qualitative and quantitative assessments (digital image analysis) of the cutaneous mononuclear cells, eosinophils and mast cells were carried out in PV patients and healthy controls (n = 10 each) following exposures to water at room temperature and warm water.

Results: Infiltration of the spongiotic epidermis and dermis by mononuclear cells and eosinophils together with edema and vasodilatation of upper dermis following warm water contact was clearly observed only in PV patients. In contrast to controls, significant increase in numbers of mononuclear cells and eosinophils in comparison with exposure to water at room temperature at the dermal-epidermal junction (p < 0.01), papillary dermis (p < 0.01) and perivascular area (p < 0.05) was found. Obvious mast cell degranulation was seen in PV sections after warm water contact, but no significant increase of their numbers was observed whether among PV patients or healthy controls (p > 0.05). However, the numbers of papillary dermal mast cells in specimens obtained from PV patients following room temperature water exposure were significantly more than those of healthy controls (p < 0.05).

Conclusions: PV represents an invisible dermatosis in which the infiltrating mononuclear cells and eosinophils may have a role in warm water-induced pruritus.