Kobner's phenomonen is the occurrence of cutaneous reactions at sites of rubbing or pressure.
Clinical classification:
(1) simple (asymptomatic)
(2) symptomatic, associated with moderate to severe pruritus
Types based on onset after stimulus:
(1) immediate (onset within 2-10 minutes)
(2) intermediate (onset in 30 to 120 minutes)
(3) late onset or delayed (onset in 4 to 6 hours)
Etiologic classification:
(1) primary
(2) secondary, associated with extrinsic factor (drug-induced, insect bites, scabies)
(3) secondary, associated with cutaneous mastocytosis
Exacerbating factors:
(1) hot bath
(2) exercise
(3) emotion
(4) cold exposure
Technical points:
(1) For monitoring a patient over time, a dermatographometer should be used, since this can monitor the amount of pressure required to produce a reaction.
(2) A standard and reproducible mark should be made, typically 10 cm in length.
(3) The same challenge area on the forearm or back should be used.
