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Hypersensitivity   Reactions
Hypersensitivity reactions (Cont’d)•   Hypersensitivity (allergy) is a state in    which the immune responses frequently  ...
Immediate hypersensitivity reactions   “antibody-mediated”Type I: Anaphylaxis•   IgE-mediated. An antigen (allergen) react...
Immediate hypersensitivity reactions (Cont’d)Type II: Antibody-dependent cytotoxic           reactions•   Antibodies of Ig...
Type II (Cont’d)Examples•   Bullous diseases (pemphigus & pemphigoid).•   DLE & SLE.•   Transfusion reactions.•   Rh incom...
Immediate hypersensitivity reactions (Cont’d)Type III: Immune complex reactions            (Arthus phenomenon)•   e.g. ser...
Delayed (Cell-mediated)Type IV: Cell-mediated or delayed-type            hypersensitivity•   Allergic contact dermatitis.
Eczema “Dermatitis”= non-specific inflammatory response of the skin to a variety of agents  which may act on skin from out...
Eczema (Cont’d)Clinical features•   It may be acute, subacute or chronic.•   It is characterized by polymorphism of erupti...
Discoid eczema•   A   coin-shaped    plaque     of   closely   set    papulovesicles or “pin-point” vesicles on an    eryt...
Seborrheic dermatitis “SD”•   It is a chronic inflammatory disease of skin    characterized by red, sharply marginated les...
Varicose eczema “Stasis dermatitis”•   There is almost always some sort of circulatory    return from the lower limbs, e.g...
Dysidrosis “Pompholyx”•   An acute or subacute vesicular or bullous eruption    (sago-like) affecting palms & soles & exte...
Treatment of prurigo nodularis withtopical capsaicin•   33 patients with prurigo nodularis of various    causes•   Capsaic...
Treatment of prurigo nodularis with topical capsaicin (Cont’d)•   1st, symptoms of neurogenic inflammation    (burning, er...
Pityriasis alba•   It is a chronic eczema of unknown origin.•   More common in children.•   Lesion: round, oval or irregul...
Contact dermatitisCD is an inflammatory reaction of the skinproduced by substances coming into contactwith the skin. There...
Contact dermatitis•   Irritant contact dermatitis      Research leading to        important   insights   to        improv...
Irritant contact dermatitis•   Caused by a substance “irritant” which, in    all subjects, produces dermatitis, if applied...
Irritant contact dermatitis (Cont’d)Two types of ICD:•   Acute ICD: result of single or very few    exposures of strong ir...
What      is      the   best   way   todiagnose           allergic    contactdermatitis?•   Patch test.
Allergic contact dermatitis “ACD”•   Caused by an external            contactant    “sensitizer” to which the        patie...
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
Medicine 6th year, Dermatology Tutorial (5th session/part one)
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Medicine 6th year, Dermatology Tutorial (5th session/part one)

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September 5th, 2011

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Medicine 6th year, Dermatology Tutorial (5th session/part one)

  1. 1. Hypersensitivity Reactions
  2. 2. Hypersensitivity reactions (Cont’d)• Hypersensitivity (allergy) is a state in which the immune responses frequently take place in such a way that cell damage occurs and harmful pathological lesions may occur.
  3. 3. Immediate hypersensitivity reactions “antibody-mediated”Type I: Anaphylaxis• IgE-mediated. An antigen (allergen) reacting with specifically sensitized IgE that is fixed to mast cells through its FC portion → degranulation of mast cells → release of their mediators, e.g. histamine, leuko- trienes & chemotactic factors (ECF & NCF).• e.g. anaphylaxis, urticaria, atopy.
  4. 4. Immediate hypersensitivity reactions (Cont’d)Type II: Antibody-dependent cytotoxic reactions• Antibodies of IgG or IgM class directed against an antigenic component either to cell membrane antigens or to antigen attached to the cell wall → cell death.
  5. 5. Type II (Cont’d)Examples• Bullous diseases (pemphigus & pemphigoid).• DLE & SLE.• Transfusion reactions.• Rh incompatibility → hemolytic disease of newborn.• In some drug reactions, e.g. sulphonamides & sedormid attached to the RBCs or platelets, respectively.
  6. 6. Immediate hypersensitivity reactions (Cont’d)Type III: Immune complex reactions (Arthus phenomenon)• e.g. serum sickness, nephritis in SLE, leucocytoclastic vasculitis, urticarial vasculitis.
  7. 7. Delayed (Cell-mediated)Type IV: Cell-mediated or delayed-type hypersensitivity• Allergic contact dermatitis.
  8. 8. Eczema “Dermatitis”= non-specific inflammatory response of the skin to a variety of agents which may act on skin from outside or inside. Endogenous eczemas Exogenous eczemas • Nummular eczema • Contact dermatitis (1ry • Seborrheic dermatitis irritant & allergic). • Stasis dermatitis. • Infectious eczematoid dermatitis. • Pompholyx. • Napkin dermatitis. • Pityriasis alba. • Exfoliative dermatitis. • Atopic dermatitis.
  9. 9. Eczema (Cont’d)Clinical features• It may be acute, subacute or chronic.• It is characterized by polymorphism of eruptions: 1ry lesions: macules, papules & vesicles. 2ry lesions: oozing, crusting, scaling, lichenification & fissuring.• The lesions aren’t sharply demarcated & itching is a common feature.
  10. 10. Discoid eczema• A coin-shaped plaque of closely set papulovesicles or “pin-point” vesicles on an erythematous base.• It is seen most frequently on back of hands & extensors of arms & legs.• Itching is usually severe.
  11. 11. Seborrheic dermatitis “SD”• It is a chronic inflammatory disease of skin characterized by red, sharply marginated lesions covered with greasy scales with a predilection for the scalp, eyebrows, nasolabial folds, retro- auricular, interscapular & sternal areas, ears, axillae, submammary folds, umbilicus & groins (seborrheic sites).• It is more common in males, between 20-40 yrs & is rare before puberty.
  12. 12. Varicose eczema “Stasis dermatitis”• There is almost always some sort of circulatory return from the lower limbs, e.g. varicose veins.• Lesions are present in the lower part of legs as an erythematous scaly oozing area surrounded by small slate-blue macules resulting from hemo- siderin deposits.• Ulceration occurring around one of malleoli usually complicates the condition.
  13. 13. Dysidrosis “Pompholyx”• An acute or subacute vesicular or bullous eruption (sago-like) affecting palms & soles & extending to sides of the fingers.• Vesicles tend to dry up in 2 weeks with desquamation of the skin.• Itching is very severe. It may be due to sweat retention or reaction to an active fungus infection of feet = Trichophytid.
  14. 14. Treatment of prurigo nodularis withtopical capsaicin• 33 patients with prurigo nodularis of various causes• Capsaicin (0.025% to 0.3%) 4 – 6x daily• 2 weeks up to 10 months• Follow-up period was up to 6 months
  15. 15. Treatment of prurigo nodularis with topical capsaicin (Cont’d)• 1st, symptoms of neurogenic inflammation (burning, erythema)• ALL experienced complete elimination of pruritus within 12 days• Skin lesions healed (gradually)• After discontinuation of the therapy, pruritus returned in 16 of 33 patients within 2 months
  16. 16. Pityriasis alba• It is a chronic eczema of unknown origin.• More common in children.• Lesion: round, oval or irregular patch, reddish in early stage & covered with fine whitish scales.• It is more common on the face.
  17. 17. Contact dermatitisCD is an inflammatory reaction of the skinproduced by substances coming into contactwith the skin. There are 3 main types:• Irritant contact dermatitis “ICD”.• Allergic contact dermatitis “ACD”.• Phototoxic & photoallergic CD.
  18. 18. Contact dermatitis• Irritant contact dermatitis  Research leading to important insights to improve therapy.  The hygiene revolution for health care workers• Allergic contact dermatitis  Type IV reactions.  Type I reactions
  19. 19. Irritant contact dermatitis• Caused by a substance “irritant” which, in all subjects, produces dermatitis, if applied on the skin for a sufficient time & in a sufficient concentration.• The main skin barriers to the entry of the external noxious substances are the stratum corneum, the surface lipid film & the sweat.
  20. 20. Irritant contact dermatitis (Cont’d)Two types of ICD:• Acute ICD: result of single or very few exposures of strong irritants usually due to an accident at work.• Chronic cumulative ICD: repeated application of weak irritants over long periods, e.g. house wives’ dermatitis.
  21. 21. What is the best way todiagnose allergic contactdermatitis?• Patch test.
  22. 22. Allergic contact dermatitis “ACD”• Caused by an external contactant “sensitizer” to which the patient is sensitized.• These sensitizers don’t usually cause skin changes on 1st exposure, but produce the eczematous reactions after repeated exposures.• The entire skin is sensitized.

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