Dermatitis

Exogenous eczema

1. Contact dermatitis:
a. Allergic.
b. Irritant.
2. Photodermatitis.
a. Phototoxic.
b. Photoallergic.
3. Infective dermatitis.

Contact Dermatitis:

It is an inflammatory response of the skin induced by substances that contact the skin surface. The responsible substance could be solid, liquid, or gas.
These substances act as irritants or allergens and may cause acute, subacute or chronic dermatitis.

Irritant contact dermatitis:

Irritation of the skin is the most common cause of contact dermatitis. It account more than 80% of all cases.

Cause:

The epidermis is a thin cellular barrier with an outer layer composed of dead cells in a water-protein-lipid matrix. Any process that damage any component of this barrier will compromises its function and a non- immunological eczematous response may result.
Strong irritants cause an acute reaction after brief contact and the diagnosis is usually obvious.
Weak irritants may need prolonged exposure, sometime over years, to cause dermatitis.
There is a wide range of individual susceptibility to develop irritant contact dermatitis which include; those with dry, fair skin and past or present atopic dermatitis double the risk of irritant hand eczema.


Investigation:
Patch test with irritants is not helpful and may be misleading.

Treatment:

Prevention is better than cure, because irritant eczema once started, it can persist for long time even after the contacts has ceased and despite the vigorous use of emollients and topical steroid.
Management is based upon avoidance of the irritants responsible for the condition which is often not possible and the best is to reduce the exposure by the use of protective gloves and clothing.
- Washing facilities at work should be good.
- Dirty hands should not be cleaned by harsh solvents.
- Barrier cream is not that helpful in established cases.
- Topical steroid and in severe cases systemic steroid.

Allergic contact dermatitis:

It is a delayed (type IV) hypersensitivity reaction characterized by:
previous contact is needed to induce allergy.
its specific to one chemical and its close relatives.
after allergy has been established, all area of the skin will react to the allergens.
sensitization persist indefinitely.
desensitization is not possible.

Investigation:

Patch test:


Treatment:
Avoid completely the offending allergen, together with symptomatic treatment of eczematous reaction by topical steroid.
Systemic steroid is used in severe cases.

Comparison between irritant & allergic

contact dermatitis:

Characteristic pointsIrritant CDAllergic CD1.People at riskEvery oneGenetically predisposed2.MechanismNon- immunologicalDelayed hypersensitivity (type-IV) reaction3.No. of exposureFew to manyOne or several4.Nature of substanceOrganic solvent, soap & detergent
Low molecular weight hapten e.g. Nickel, fragrance, hair dye
5.No. of compoundManyFew6.Concentration of substanceUsually highMay be very low7.DistributionLocalizedMay spread beyond area of contact
8.OnsetGradualRapid9.InvestigationNonPatch test

Photodermatitis:

Phototoxic:
This type of reaction require a drug that will absorb UVR and cause the reaction.

Clinically:

Tenderness and redness occur only in area that exposed to sufficient drug and to sufficient UVR. Severe cases is painful and the skin may blister.
The skin may later develop a deep tan.
The reaction are not immunological, everyone exposed to enough drug and to enough UVR will develop this reaction.
Localized phototoxic dermatitis (phytophotodermatitis) may occur due to contact with psoralens in plants. The area burn and may blister, leaving pigmentation in linear streaks and bizarre pattern.


Photoallergic:
Drugs (topical & systemic) and chemicals on the skin can interact with UVR and cause immunological reaction.
Many of the same drugs that cause phototoxic reaction can also cause photoallergic ones.
UVR covert an immunologically inactive form of drug into an antigenic molecule and induce an immunological reaction similar to allergic contact dermatitis.
The eruption occurs on the exposed area such as the hand, the V of the neck, nose, chin, and forehead, with sparing of the upper lip under the nose, the eyelids and the submental area.

Characteristic

pointsPhototoxicityPhotoallergy1. PresentationErythema & smooth
(may blister)Eczematous & rough
(may weep)2. OnsetImmediateDelayed, (may not occur on first exposure)3. SymptomHurtsItch4. Photo-patch test- ve.+ ve.

Drugs commonly causing photodermatitisAmiodarone

Chlorpropamide
Nalidixic acid
Oral contraceptive
PhenothiazinesPsoraline
Quinidine
Sulphonamides
Tetracyclines
Thiazides


Treatment:
stop the offending drugs.
avoid further exposure to sunlight (avoidance, clothing, sunscreen).
potent topical steroid.
short course of a systemic steroid in severe cases.

Infective dermatitis:

Its an acute dermatitis probably caused by bacterial infection of the skin in susceptible individuals.
The exact mechanism is unknown , but the product of the infection together with the therapeutic agent applied may play a role in the sensitization of the skin.
The eczematous patch slowly develop around the primary sites, like infected wound, discharching sinus, discharching ear, insect bite or parasitic infection.
It consist of red, oozing, heavily crusted lesion which tend to spread peripherally. The eruption may become subacute or chronic with tendency to relapse.

Treatment:

treating the underlying cause.
topical anti inflammatory with antibiotics.









PAGE 

PAGE 1