September 5th, 2011

1. Hypersensitivity
Reactions

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. 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.

5. 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.

8. 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.

9. Immediate hypersensitivity reactions (Cont’d)
Type III: Immune complex reactions
(Arthus phenomenon)
• e.g. serum sickness, nephritis in SLE,
leucocytoclastic vasculitis, urticarial
vasculitis.

11. Delayed (Cell-mediated)
Type IV: Cell-mediated or delayed-type
hypersensitivity
• Allergic contact dermatitis.

13. 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.

14. 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.

15. 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.

19. 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.

24. 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.

26. 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.

33. Treatment of prurigo nodularis with
topical 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

34. 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

36. 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.

38. Contact dermatitis
CD is an inflammatory reaction of the skin
produced by substances coming into contact
with the skin. There are 3 main types:
• Irritant contact dermatitis “ICD”.
• Allergic contact dermatitis “ACD”.
• Phototoxic & photoallergic CD.

39. 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

43. 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.

44. 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.

45. What is the best way to
diagnose allergic contact
dermatitis?
• Patch test.

48. 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.