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Query: UMLS:C0030193 (pain)
 261,466 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Itch is a distinct sensation arising from the superficial layers of skin and mucous membranes. It is elicited by histamine and probably other endogenous chemicals that excite subpopulations of unmyelinated primary afferents and spinal neurones projecting through the anterolateral quadrant to the brain. The two popular views, which propose either that itch is signalled by a labelled line system of peripheral and central itch-specific neurones or that itch is the subliminal form of pain, both fail to explain convincingly many known features. Alternative theories emphasize central processes that extract the relevant information from afferents with broad sensitivity spectra for pruritogenic and noxious stimuli. Thus, itch presents an irritating challenge for the specificity theory of somatosensation.
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PMID:Itching for an explanation. 128 50

A quantitative comparison was made of the effect of infiltration of local analgesics and topical analgesic cream (EMLA) on laser-induced pain and histamine-induced wheal, flare and itch. Wheal and flare were quantified by planimetry and analgesia was quantified by the pricking pain threshold to argon laser stimulation. The intensity of histamine-induced itch was scored on a 4-point scale. Local analgesics had no effect on the wheal area. The flare reaction was abolished by infiltrating lignocaine, and gradually inhibited by increased application times of EMLA. Itch was abolished after local lignocaine infiltration, but not significantly reduced after EMLA cream applied for less than 120 min, although the skin was anaesthetized to laser-induced pain. The reduction of flare area correlated to the level of analgesia, which may therefore reflect the cutaneous responsiveness to neurogenic inflammation. It is suggested that itch and pricking pain are mediated by different populations of nerve fibres, as itch can be evoked even when the sensation of pricking pain is abolished. Surgery, skin prick tests and other traumatic procedures should therefore be performed under local anaesthesia to reduce neurogenic inflammation.
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PMID:A quantitative comparison of the effect of local analgesics on argon laser induced cutaneous pain and on histamine induced wheal, flare and itch. 196 96

Itch was assessed both continuously using a computerized method, Pain-Track, and retrospectively using visual analogue scales (VAS) by 28 patients undergoing maintenance hemodialysis and suffering from uremic pruritus. Measurements were performed during 7 consecutive days including three dialysis sessions. Pain-Track recordings showed that itch intensity was greater during dialysis than on days following dialysis (p less than 0.05). Possible explanations are that pruritogenic substances might be released during treatment or that removal of such substances during dialysis leads to amelioration of symptoms after treatment. Alternatively, lowering of the sensory threshold due to general discomfort in association with dialysis may exacerbate the itch intensity. There was no consistent difference between daytime and bedtime itch scores over the week, except on the second day without treatment, when bedtime itch ratings significantly exceeded those during the day (p less than 0.05), suggesting that factors other than inactivity are essential for this peak in itch intensity. Thus, after 2 days without treatment, when patients become increasingly metabolically deranged, they reported maximal itch, implying that the accumulation of pruritogenic substances is of major importance in the pathogenesis of uremic pruritus. There was a positive correlation between Pain-Track and VAS data, although significant fluctuations in itching could be detected only with Pain-Track.
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PMID:Computerized recording of itch in patients on maintenance hemodialysis. 257 7

One thousand two hundred women, aged 61, randomly selected from a defined geographical area in South Sweden, were interviewed by an anonymous questionnaire about their urogenital symptoms. Seventy-five percent co-operated, of whom 29.2% admitted to some degree of urinary incontinence and 48.8% some degree of lower genital tract disorder. Stress incontinence symptoms were reported by 11.8% of the women, urge incontinence by 7.9% and both types combined--"mixed" by 9.5%. Four percent of all women (18% of stress incontinence) experienced a loss sufficient to necessitate the wearing of a sanitary napkin or change of under clothing several times a day. Thirteen percent had repeated urinary tract infections. Itch, discharge and smarting pain was reported by 15%. Thirty-eight percent had vaginal dryness and dyspareunia. Only 4% of the women were undergoing estrogen therapy.
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PMID:Prevalence of genito-urinary symptoms in the late menopause. 673 Sep 43

Measurement in its broadest sense can be defined as the assignment of numerals to objects or events according to rules. The rules settle the scale level, which in turn determines the mathematical and statistical operations permissible when handling the data. Itch is a subjective symptom that can be assessed only by the subject himself. No animal models are established for the investigation of itch. In contrast to pain research, a field with many similarities, rather few scientific attempts have been made to develop and evaluate methods for the quantitative analysis of itch. However, several investigators have recently addressed the challenge of itch measurement in both experimental and clinical situations. This is important, as valid quantitative techniques for the assessment of itch are of considerable value for studying the mechanisms of pruritus, and for the evaluation of antipruritic therapies.
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PMID:Measurement of itch. 867 32

No adequate topical therapy is available for pruritus. As little is known about the local influence of antihistamines and topical anaesthetics on the pruritic effect of histamine, we studied these agents in 12 volunteers. The antipruritic effect of 15-min topical application of dimethindene maleate (Fenistil gel) and different agents (Optiderm, EMLA, Xylocaine-Salbe 5%) on subsequent focal histamine stimulus (20 mC) given by iontophoresis was evaluated. The results were compared with those of pretreatment with the corresponding placebo creams and observations on skin. Wheal and flare areas were evaluated planimetrically. Itch or pain ratings were entered on a scale every minute over a 24-min period. The examination also comprised alloknesis, i.e. elicitation of perifocal itch sensation by usually non-itch-inducing (e.g. mechanical) stimuli. Remarkably, all topically applied substances, regardless of antihistaminic or anaesthetic potential, reduced the area of alloknesis significantly. This is likely to be a result of diminished excitability of the cutaneous mechanoreceptors. Itching was significantly reduced by all active substances, including the placebo cream corresponding to Optiderm, which might be due to the presence of urea.
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PMID:[Antipruritic effect of antihistaminic and local anesthetic topical agents after iontophoretic histamine stimulation]. 870 80

Topically administered ketorolac (Acular), a cyclooxygenase inhibitor, has recently been reported as clinically beneficial for treating allergic conjunctivitis. The ability of ketorolac to relieve the itching associated with allergic conjunctivitis is intriguing because cyclooxygenase inhibitors are not regarded as useful in treating allergic dermatoses and prostaglandins (PG) do not elicit an itch response in human skin. To gain further insight into the mechanisms involved in the antipruritic activity of ketorolac, we used a method of reproducibly assessing ocular surface itch responses in the guinea pig. The measurement of conjunctival pruritus involved a recently developed behavioral model whereby hind limb scratching episodes directed toward the afflicted area were quantified. Itch-scratch episodes have previously been delineated from foreign body and pain sensations, which do not evoke such a behavioral response. Ketorolac significantly inhibited the itching associated with experimental allergic conjunctivitis. The basis of this antipruritic activity may be ascribed to preventing the biosynthesis of itch-producing PGs because ketorolac inhibited arachidonic acid-induced pruritus. In contrast to skin studies, PGE2 and PGI2 were found to be potent pruritogens at the guinea pig ocular surface. PGD2 was a weak pruritogen, and PGF2 alpha and the thromboxane-mimetic U-46619 produced no meaningful response. Further studies involving selective agonists and antagonists suggested that EP1 receptors, IP receptors and PGD2-sensitive receptors may mediate prostanoid-induced conjunctival itching. No evidence for the involvement of other prostanoid receptor subtypes was obtained. Although the EP1 receptor antagonist AH 6809 and the DP receptor antagonist BW A868C inhibited PGE2- and PGD2-induced itching, respectively, neither antagonist alone significantly affected the itching associated with experimental allergic conjunctivitis. A combination of AH 6809 and BW A868C, however, did exhibit antipruritic activity. It appears that for effective relief of itching in allergic conjunctivitis, it is not sufficient to block the effects of a single pruritogenic PG. It is preferable to reduce the participation of all pruritogenic PGs by either using combined receptor antagonists or by using a cyclooxygenase inhibitor such as ketorolac to block their biosynthesis.
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PMID:Characterization of receptor subtypes involved in prostanoid-induced conjunctival pruritus and their role in mediating allergic conjunctival itching. 885 86

Scratching the skin, while instantly relieving itch, often aggravates itch over time due to skin injury. To relieve itch, without damaging the skin, a new technique termed cutaneous field stimulation (CFS) was developed and tested on 21 subjects. CFS uses a flexible plate with needle-like electrodes (n = 16) to electrically stimulate nerve fibres in the superficial skin. The electrodes were stimulated consecutively (4 Hz per electrode, pulse duration 1 ms, intensity 0.4-0.8 mA, 25 min). CFS resulted in a pricking and burning sensation that usually faded rather quickly. The burning sensation was still present during a selective block of impulse conduction in myelinated fibres indicating that nociceptive C-fibres are activated by CFS. Furthermore, a flare reaction developed around the CFS electrodes indicating activation of axon reflexes in nociceptive C-fibres. Itch, elicited by transdermal iontophoresis of histamine, was abolished within the skin area pre-treated with CFS, and was reduced to 14% of control 10 cm distally. Contralateral effects were small or non-existent. After 4 h, itch was reduced ipsilaterally to 32% of control. In comparison, 2 h after transcutaneous electrical nerve stimulation (TENS; 10-20 mA, 100 Hz, 25 min) ipsilateral itch was reduced to 56% of control. In conclusion, CFS offers a powerful new method for combating itch. It is suggested that CFS acts through endogenous central inhibitory mechanisms that are normally activated by scratching the skin.
Pain 1997 May
PMID:Cutaneous field stimulation (CFS): a new powerful method to combat itch. 920 Jan 73

We investigated the antipruritic effect of a 15-min application of dimethindene maleate (Fenistil gel) and other local analgesics (Optiderm, EMLA, Xylocain ointment 5%) on subsequent focal histamine stimulus (20 mC) given by iontophoresis in 12 patients suffering from acute atopic eczema (AE). The results were compared to histamine after pretreatment with the respective placebo and to non-pretreated skin. Wheal and flare areas were planimetrically evaluated. Itch or pain ratings were performed over a 24-min period using a rating scale. The examination also comprised alloknesis, i.e. induction of a perifocal itch sensation by a non-itching mechanical stimulus. None of the antihistaminic and anaesthetic agents reduced the itch intensity significantly. Three of the AE patients had a total lack of alloknesis. We conclude that these substances, when applied for 15 min, are not sufficiently effective in atopic skin suppressing histamine-induced reactions under experimental conditions. The diminished elicitation of alloknesis in these patients may be a result of central nervous system alteration.
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PMID:Experimentally induced pruritus and cutaneous reactions with topical antihistamine and local analgesics in atopic eczema. 941 92

Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide) is thought to produce analgesic and possibly also antipruritic effects when applied topically. Capsaicin 0.05% was applied three times daily over a 5-day period to the same infrascapular region. The effects of the pretreatment upon the pruritogenic and wheal and flare reactions to subsequent histamine iontophoresis (20 mC) were evaluated on the following day. The antipruritic effects of the pretreatment were compared with the effects of placebo pretreatment and no pretreatment. Wheal and flare areas were evaluated planimetrically. Itch or pain were rated every minute over a 24-min period. The areas of alloknesis, i.e. the induction of perifocal itch sensation by usually nonitching (e.g. mechanical) stimuli, were also evaluated. In control subjects, but not in atopic eczema (AE) patients, capsaicin pretreatment significantly reduced the flare area. Compared with control subjects, AE patients showed a lack of alloknesis or significantly smaller areas of alloknesis in pretreated and nonpretreated skin. In control subjects, capsaicin pretreatment significantly reduced itch sensations compared with nonpretreated skin, whereas in AE patients no differences were seen. Itch sensations in capsaicin-pretreated skin were significantly lower in control subjects than in AE patients. We conclude that capsaicin does effectively suppress histamine-induced itching in healthy skin but has less effect in AE. The diminished itch sensations and the absence of alloknesis in atopic individuals indicate that histamine is not the key factor in itching in AE.
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PMID:Effect of topical capsaicin on the cutaneous reactions and itching to histamine in atopic eczema compared to healthy skin. 970 61


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