By Dr. Giovambattista Virga
THE SYMPTOM
Pruritus is an unpleasant cutaneous sensation prompting a desire to scratch. It is a common and disturbing symptom among patients (pts) receiving hemodialysis (HD). The percentage of HD pts suffering from pruritus varies reportedly from 50% to 90% [1,2,3,4,5,6,7]. Interestingly, pruritus is typically not seen in acute renal failure [8].
PATHOPHYSIOLOGY
Itch is transmitted by dedicated C neurons and the proximity of dermal mast cells to afferent C neurons has suggested a functional relation between these two cell types: mast cell activation releases tryptase, which activates a receptor localised on C fibre nerve terminals that transmit the itching sensation to the central nervous system. Additionally, receptor activation will lead to a local release of substance P that activates dermal mast cells, resulting in an increased release of TNF- which in turn sensitises nociceptor nerve terminals and enhances their responsiveness [9]. Substance P, a neurotransmitter widely distributed in the afferent sensory neurons, can communicate pain and some itching sensations from the periphery to the central nervous system and is considered potentially responsible for itching [10,11]. It is a potent vasodilator and may serve as a mediator for axon reflex vasodilatation [12].
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