Patch test is a type of: (AIIMS Nov 2014)
|B||Antibody mediated Hypersensitivity|
|C||Immune complex mediate Hypersensitivity|
|D||Delayed type Hypersensitivity|
Delayed type Hypersensitivity
1). Patch test is done to confirm the diagnosis in Allergic contact dermatitis.
2). The suspected allergen is applied on upper back along with a control.
3). The results are recorded at days 2 and 4 and it is read as :
4). Patch test positive at day 2 and negative at day 4 is an irritant reaction. False positive irritant reactions are liable to induce stronger reactions at 2 days than at 4 days- known as crescendo-decrescendo effect.
Allergic Contact Dermatitis
1). It is type IV (delayed type) hypersensitivity
2). Diagnosis is made by patch test (read after 48 hours)
3). Most common cause:
a. Air borne contact dermatitis à Parthenium (Congress Grass)
b. In Indian females à Detergents
c. Metals àNickel (Ni)
Contact dermatitis types:
It is an inflammatory process in skin which is caused by an exogenous agent that directly or indirectly injure skin.
Irritant Contact Dermatitis (ICD)
Allergic contact dermatitis (ACD)
a. Caused by inherent characteristic of a compound eg acid or base
b. Strictly demarcated & often localized to areas of thin skin (eyelids, intertriginous areas) or to areas, where irritant is applied.
c. Chronic low grade irritant dermatitis is the most common type of ICD, and most common area of involvement is the hands.
d. - The most common irritants encountered are chronic wet work, soaps and detergents.
a. Agent causing ACD induce an antigen specific immune response. (delayed type hypersensitivity mediated by memory T lymphocytes).
Hair dye- PPD
Bindi - PTBP
Cement- sodium dichromate