An<unk>  (Latin: pruritus) is a sensation felt on an area of skin that evokes the desire or reflex to scratch that area.<unk> ing can be related to anything from dry skin to cancer. <unk>  has many similarities to pain and both are unpleasant sensory experiences but their behavioral response patterns are different. Pain creates a reflex withdrawal while<unk>  leads to a scratch reflex. Unmyelinated nerve fibers for<unk>  and pain both originate in the skin, however, information for them are conveyed centrally in two distinct systems that both use the same peripheral nerve bundle and spinothalamic tract.
Until recent times, sensations of<unk>  were considered to be largely the same as those of pain. Currently, pruritus is considered to be an autonomous, pain-independent sensation.<unk> , also known as medically pruritus, The first documented definition of<unk>  was given by the German physician Samuel Hafenreffer as an “unpleasant sensation that elicits the desire or reflex to scratch” about 350 years ago. In recent years, pruritus has been determined to be an autonomous, pain-independent sensation.
pruritus is a frequently misspelled word, often misspelled as "pruritis".
Historically, the sensations of<unk>  and pain have not been considered to be independent of each other until recently where it was found that<unk>  has several features in common with pain but exhibits notable differences. Pruritic stimuli mostly create the same reactions as noxious stimuli in experimental animals. As a result, it is difficult to study the physiologic mechanisms of<unk>  in animal models as they lack the ability to discern the differences between both stimuli. Therefore human studies have provided most of the information regarding the processing of pruritic stimuli. It was initially thought histamine was the major chemical involved in mediating pruritus through binding to H1R and activating phospholipase Cβ3 (PLCβ3) and phospholipase A2 (PLA2). Bell et al. demonstrated that histamine promotes the influx of calcium at the axon terminals of the spinal cord neurons via a transient receptor vanilloid 1 (TRPV1) receptor activation and then, through the promotion of a series of intracellular signal activation, eventually lead to the generation of<unk> ing sensation. However, the current consensus is that there are other chemical mediators that are highly involved in the promotion of pruritus.
The pathogenesis of<unk>  is characterized by  dermal/pruritoceptive which originates in the skin, neuropathic which is due to damage along the afferent pathway of a nerve, neurogenic<unk>  which originates centrally without the involvement of the peripheral nerves, a psychogenic<unk>  which is associated with psychiatric disorders and phobias, and a mixed picture which is due to two or more causes of<unk> ing
There are many causes of<unk> ing. Examples include skin diseases, systemic diseases, allergies, medications, insect stings among many others
There is a very broad differential diagnosis for<unk> ing due to an extensive list of possible causes.<unk> ing may be due to dermatologic disease, systemic disease, reactions to chemicals and medications, weather, or psychiatric disease. Symptoms, laboratory findings, and other diagnostic tests can help narrow down the list.
About 280 million people globally, roughly 4% of the world's population, have difficulty with<unk> iness.
pruritusmay be associated with virtually any malignancy. Certain neoplasms, especially hematologic malignancies, have pruritus as a common symptom. For example, in patients with polycythemia vera, 48% to 70% have aquagenic pruritus, which is<unk> ing that is associated with water coming in contact with the skin. Also, about 30% of people with Hodgkin's disease suffer from pruritus. The incidence of pruritus in other types of hematologic malignancies is currently not known, however, investigators have reported its presence in approximately 3% of patients with non‐Hodgkin's lymphoma. Solid tumors may be associated with paraneoplasticpruritus. In fact, pruritus may one of the early symptoms, starting months or years before a patient is diagnosed. pruritus is also a frequent finding in cutaneous lymphomas. Additionally, it is frequently seen in cancers involving the biliary tract. Retrospective studies have revealed that 2% to 11% of chronic<unk>  cases are attributable to malignancies.
pruritus has been reported to be an early symptom in some non-malignant diseases such as liver disease, renal insufficiency, thyroid disease, Sjögren's syndrome, diabetes mellitus, iron deficiency, paraproteinemia, and other conditions. In internal diseases,<unk>  has been best studied in cholestatic pruritus and uremic pruritus.
About a third of uremic patients treated without dialysis complain of uremic pruritus, and on maintenance hemodialysis, the incidence of uremic<unk> ing rises to 70%-80%.
Cholestatic pruritus]] affects nearly if not all patients with biliary cirrhosis and is the first symptom in nearly 50% of the patients with this disease. Furthermore, the prevalence of pruritus in patients with end‐stage HIV is over 20%.
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