Clinica

The International Journal of Artificial Organs / Vol. 29 / no. 10, 2006 / pp. 938-943

Artificial Kidney and Dialysis

Uremic pruritus
G.C. KOSMADAKIS, N. ZEREFOS
Dialysis Unit, “Hygeia” General Hospital, Athens - Greece

ABSTRACT: Renal itch is a localized or generalized itch, affecting patients with chronic renal failure, where there is no primary skin disease and no systemic orpsychological dysfunction that might cause pruritus. Uremic pruritus (UP) is an unpleasant sensation, rarely appearing in earlier stages of chronic kidney disease. Renal transplantation is the definite solution for that problem. The prevalence of UP has been reduced during the last years, possibly, due to a more efficient dialysis, with more biocompatible filters. During the last decades a big number ofsubstances were considered to be etiologic factors of UP, and an even bigger number of therapeutic substances appeared with promising potentials and conflicting results in the course of their use. The main reason for this disorientation is the lack of sound evidence on the pathogenetic mechanisms that may potentiate UP. 'Inflammatory' and 'opioid' hypothesis are the best studied and the reductionof UP is a fact. Nevertheless the mechanisms of the pathogenesis of UP are still under investigation and a long way has to be done in order to achieve more definite results. (Int J Artif Organs 2006; 29: 938-43) KEY WORDS: Uremia, Pruritus, Dialysis

Pruritus or itching, an “unpleasant cutaneous sensation that provokes the desire to scratch”, is a common symptom of patients with chronic renalfailure disorder (13). In hemodialysis (HD) patients it can prove to be a devastating problem that affects the quality of life and may lead to psychiatric disorders and even suicide attempts. Peritoneal dialysis patients also suffer from uremic pruritus (UP). In recent years its prevalence has been reduced, possibly because of more efficient dialysis with improved biocompatible membranes. Yet itsunderlying pathogenetic mechanism remains poorly understood, with many substances implicated in its etiology; and even more therapeutic substances have appeared with promising potentials and conflicting results. Importantly, uremic pruritus is cured by renal transplantation, so that transplanted patients, even with severely impaired renal function, do not suffer from it (3-5). In clinical studiespruritus is usually assessed by subjective methods. A visual analog scale and a specially adapted questionnaire scoring method are the most frequently used (6-8).

Neurophysiology
Neurophysiological research has led to the accurate definition of the neural pathways of itching and confirmed that they are distinct from those for pain (9). At the periphery a pruritogen stimulates the free endings ofunmyelinated Cnerve fibers, which are anatomically identical to those associated with the mediation of pain and can be stimulated directly (histamine, kallikrein IL-2, acetylcholine) or indirectly via histamine release from local mast cells (VIP, substance P, serotonin, bradykinin etc). The impulses are conveyed to the dorsal horn of the spinal cord, then travel via the spinothalamic tract to thethalamus and on to the somatosensory cortex. There is at present no convincing evidence for the existence of an “itch centre in the brain” (1). Itching may be peripheral (pruritoceptive) or central (neurogenic or neuropathic) (9). Neuropathic itch can originate at any point along the afferent nervous pathway as a result of damage to the nervous system. Neurogenic itch is induced centrally in theabsence of nervous system damage and is often associated with the accumulation of
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0391-3988/001-06 $15.00/0

Wichtig Editore, 2006

Kosmadakis and Zerefos

endogenous (e.g. in cholestasis) or exogenous opioids. Psychological factors and psychiatric disorders also play a role in the induction of itch of central origin.

lower dialysis efficacy estimated by Kt/V urea and normalized...