Skin and serum levels of calcium, phosphorus and vitamin D3 in uremic pruritus patients before and after broad band ultraviolet B (UVB) phototherapy

Background: Pruritus is one of the commonest frustrating manifestations in chronic renal failure. The exact cause of uremic pruritus is unknown and several factors are reported to be involved in its pathogenesis, the most important of which are abnormalities in calcium and phosphorus metabolism. Broad band UVB phototherapy plays an important role in treatment of uremic pruritus through different mechanisms. Aim of work: The aim of this work was to evaluate skin and serum levels of calcium and phosphorus and their regulating hormone, vitamin D Egyptian Dermatology Online Journal Vol. 1 No 2:1, June 2006 2 in uremic patients before and after broad band UVB phototherapy to verify their role in the pathogenesis of uremic pruritus. Patients and Methods: The study included 18 patients of uremic pruritus and 9 controls. A 4 mm punch biopsy and 5cm blood sample were taken from all patients before and after UVB phototherapy (when patients reported clinical disappearance of itching). Similar samples were taken from controls before the start of the study. Results: The serum and skin calcium in uremic patients before UVB phototherapy were lower than the controls, and they increased significantly after phototherapy. The serum levels of calcium were normalized after phototherapy. On the other hand, though the skin content of calcium was increased significantly after phototherapy, it was still significantly less than controls. The serum phosphorus in uremic patients before UVB phototherapy was higher than the controls, and it decreased significantly after UVB phototherapy, though it remained significantly higher than controls. On the other hand, skin content of phosphorus in uremic patients before UVB phototherapy was less than in controls, and it decreased significantly after UVB phototherapy. Serum and skin contents of vitamin D in uremic patients increased significantly after UVB phototherapy. Conclusion: It appears from this study that hyperor hyperphosphatemia may represent a circulating pruritogenic substance that stimulates itching pathways in uremic patients. In addition, we postulate that hypocalcaemia and low skin calcium content, together with the previously reported disrupted calcium ion gradient, may have a direct relation to the stimulation of itching pathways. The main role of UVB in improving pruritus may be related to its systemic normalizing effect on both calcium and phosphorus (increasing calcium and lowering phosphorus).