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dr. Eddy Karta, SpKK7 November 2006
Pruritus
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Pruritus
An unpleasant sensation provoking the desire to scratch
Definition:
Samuel Hafenreffer, 1660
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Classification of different type of itch
•Pruritoceptive itch (inflamation, dryness, skin damage)
•Neuropathic itch (pathology along aferent pathway)
•Neurogenic itch (central without neural pathology)
•Psychogenic itch (psychological abnormalities)
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Etiology
External•Clothing: wool, fabric softener•Ectoparasite: Sarcoptes scabiei•Insect bite•Climate: dry cold•Infection: viral, bacterialInternal•Pruritic skin diseases: prurigo•Hypersensitivity•Drug side effect: morphin, barbiturate•Systemic diseases•Psychologic disorder
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Non itch Itch80%
5 %15 %
Mechano-insensitive nociceptors ( not respond to mechanical, respond to chemical)
Polymodal nociceptors “CMH”(respond mechanical,heat and chemical stimuli)
Relative proportion of mechano-responsive and mechano-insensitive unmyelinated nociceptors
in human skin nerves.
(histamine -) (histamine +)
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Innervation of itch sensation
• sensory neurons have a unipolar cell body• The axon: unmyelinated C fiber, end in
dermo epidermal junction mechano insensitive C fiber
• Neuronal pathway: sensory part dorsal horn cross over spinal cord to contralateral side lateral spinothalamic tract thalamus sensory motor cortex
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The neuroanatomy of pruritus of cutaneous origin
Pruritogen
Free nerve endings
Unmyelinated C nerve fibers
Dorsal horn of spinal cord
Contralateral spinothalamic tract
Postolateral ventral thalamic nucleus
Somatosensory cortex(post central cingulate gyrus)
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Main classes of mediators causing itch in inflamed skin
Amines Proteins/peptidesHistamine KallikreinHistamine liberators Cytokines morphine, codeine IL-2Serotonin Proteases
trypsinLipids chymaseProstaglandines TachykininsPlatelet activating factor substance P
CGRP (calcitonin gene-related peptide) VIP (vasoactive intestinal peptide)Opioid peptides βendorphins leu encephalin met encephalin
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Inflamatory mediators divided by mechanism
Direct stimulation of itch-specific C-fibersHistamine +++Papain +++Kallikrein +++Interleukin-2 +++Acethylcholine +*
Effect via histamine-releaseChymase (triptase) +++Trypsin (tryptase) +++Substance P ++Serotonin +Bradykinin (+)
Weak or no pruritogenic effect; potentiates histamineProstaglandins (+)
* In atopy; causes pain in non-atopic subjects
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Pruritic mediators
Histamine• two main subclass: H1 and H2 receptors in skin• H1 receptor caused itch• Main source: dermal mast cell
Serotonin• Causing itch centrally and peripherally• Peripheral: indirect trough release of histamine
Cytokine• inflammatory chemical • Produced by: keratinocyte, fibroblast, and mast cell• Interleukin-2 (IL- 2)
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Pruritic mediators
Tachykinins•Neurokinin A (NKA), Substance P(SP), Calcitonin gene related peptide (CGRP) Vasoactive intestinal Peptide (VIP)•Release from nociceptive C fiber•Plays roles in inflammation•SP: histamine release from mast cell
Protease•Mast cell mediators: Tryptase, chymase •Have direct pruritic effects
Opioid• pruritic effect centrally and peripherally
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Itch evokes the behavior of scratching which increases inflammation and causes excitation of nerve fibers, leading to more itching and scratching.
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Evaluation of itch without obvious case
History•Periodicity (day or night, intermitent or continuous)•Nature (burning, prickling, insects crawling)•Location (palms of hands and soles of feet)•Provoking factors (activity/exercise, cold, sunlight, water)•Medications (opioid, hypersensitivity reactions)•Atopic history•Travel history
Thorough examination•Dry skin?•Skin lesions?•Any systemic abnormalities?
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Eyes, eyelids:Allergic blepharitisAllergic conjunctivitisAtopic dermatitisAllergic contactdermatitis
Nose:Allergic rhinitis
Arm:Brachioradialpruritus (lateral)Xerotic eczemaEczematousdermatitis(antecubital)
Trunk:ScabiesAllergic contactdermatitis
Groin:Tinea crurisErythrasmaAllergic contactdermatitisIntertrigoPediculosisScabies
Hands:Dyshidrotic eczema(pompholyx)Allergic contact dermatitisScabies (web spaces)
Vulva (pruritus vulvae)
Legs:Xerotic eczema (shin)NeurodermatitisStasis dermatitisAtopic dermatitis (popliteal fossa)Lichen simplex (lateral malleolus)Dermatitis herpetiformis (knee)
Scalp:PediculosisPsoriasisSeborrheic dermatitisAllergic contactdermatitisPustule
Back:NotalgiaparestheticaXerosisPsoriasisFolliculitis
Ear canal:OtomycosisOtitis externa (early)Allergic contactdermatitisSeborrheic dermatitisPsoriasis
Anus:Pruritus aniAnal fissureCondylomaacuminatumPinworms
Feet:Tinea pedisEczematous dermatitisAllergic contact dermatitisScabies (interdigital)
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Systemic causes of pruritus
CholestasisChronic renal failureEndocrine origin
hyperthyroidismdiabetes mellitus
Haematologic abnormalitiesHodgkin lymphomaSezary syndromepolycythemia veraIron deficiency anemiaMastocytosis
InfectionsHIV
Parasitic infectionsSclerodermaRapid Weight loss in Eating disorders
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You know that I would cut offMy hands to help you
But if I did I wouldn’t haveAnything to scratch with
And then I’d be ofNo use at all.
Don Mc Gonigal, The Itch, 1991
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Thank You