CORRELATION BETWEEN THE SOURCE AND NATURE OF
ALLERGENS, THE LOCATION OF CONTACT ECZEMA LESIONS, AND CLINICAL SIGNS
Contact allergens may reach the skin in several
different ways (1)
-
By direct application or contact with an
allergen or an allergen-contaminated surface.
-
By airborne exposure to vapors, droplets, or
particles that are released into the atmosphere and then settle on the skin.
-
By contact with people (partners, friends,
colleagues) who transmit allergens to cause "connubial" or
"consort" dermatitis.
-
By transfer from other sites on the body,
generally the hands, to more sensitive areas like the mouth region or the
eyelids. This is what is called
"ectopic" dermatitis.
-
By systemic exposure in previously sensitized
patients, the result being flare-up reactions on a previously affected site or
reactions away from the original site, as is the case with dyshydrotic hand
eczema.
-
By an id-like spread of a contact dermatitis
reaction elsewhere on the body.
-
In association with exposure to the sun if
photo-allergens are involved.
1. Correlation between the source and nature of
the allergen and the location of contact eczema lesions
In
general, contact dermatitis occurs in the area of the skin that comes in
contact with the causal substance and, if it is allergic, generally extends
beyond the specific area of application of the allergenic substance. Precise topographical analysis of contact
dermatitis in function of the anamnesis is indispensable.
In
professional dermatitis, the establishment of a correlation between the
specific professional movements and the topography of the cutaneous lesions is
very important (for example, handling tools, which involves certain skin areas
of the palms of the hands). Nevertheless,
there are situations where the allergic contact eczema does not occur in the
area of contact. Thus, the lesion
topography can be strongly determined by factors influencing the penetration of
the allergen. For example, a hand
dermatitis caused by liquids or powders is often located on the back of the
hands and the lower arms and very often not on the palms, which have a
particularly thick corneal layer. In
the same way, even though an allergen may be manipulated by the hands, the
allergic dermatitis may occur only on the face, for example, on the upper
eyelids where the skin is particularly delicate. This is typical for an allergy to nail polish, but is also seen
with chemical products that are handled in a professional context.
An
airborne dermatitis is characterized by the occurrence of the dermatitis on
air-exposed areas (so it is often difficult to differentiate from a
photo-dermatitis) and often by the symmetrical involvement of the areas
(eyelids, neck, back of the hands, etc.).
Reactions at remote body sites as well as the so-called "endogenous"
contact dermatitis reactions caused by systemic exposure to the allergen,
however, are also often symmetrical.
2. Correlation between the nature of the allergen and the clinical
signs
In
general, one cannot predict patch testing outcomes by observing the clinical
patterns of contact dermatitis or by morphology (2). However, there have been several cases in which the clinical
signs the patient presents suggest the nature of the allergen. Some examples are linear lesions in plant
dermatitis, hyperkeratotic lesions on the palms in patients in contact with
rubber tools, streaking lesions on the face indicating an allergy to nail
varnish, patchy and well-defined lesions suggesting contact allergy to
isothiazolinone derivatives (or other preservative agents), papulo-vesicular
lesions to nickel and follicular lesions caused by emulsifiers.
1.
Dooms-Goossens A, Debusschere K, Gevers D,
Dupré‚ L, et al. Contact dermatitis
caused by airborne agents. JAAD 1986,
15:1-10.
2.
Storrs FJ.
All the things I knew were true about contact dermatitis that
aren't. Cutis 1993, 52:301-306.