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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