Medicine 6th year, Dermatology Tutorial (5th session/part one)
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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
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
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.
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.
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
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.
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.
What is the best way todiagnose allergic contactdermatitis?• Patch test.
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.