Mechanism of injury

Most insults can be classified as chemical, biological or physical in origin. Contact with allergens can arise from immersion of usually the hands but sometimes the legs. It may arise from direct handling of contaminated substances or from workbenches, tools or clothing. Splashing may occur or dust in the air, such as cement dust.

Chemical

More than 3,000 chemicals have been found to produce contact dermatitis in humans. They include acids, alkalis, water, salts of heavy metals, aldehydes, alcohol, esters, aromatic hydrocarbons, solvents and metallo-organic compounds.

Biological

Plants, animals, fungi, bacteria, arthropods and insects are amongst the offenders.

Physical

Heat, cold, variations in humidity, various wavelengths of light and ionizing radiation can all damage skin.

Presentation

The presentation and pattern of skin change may give some indication of the likely irritant. Hands are the most frequently affected with direct contact. Chemicals on clothing may produce changes in axillae, groins and feet. Dust irritants are most likely to cause problems in areas where the dust might collect such as collar line, belt line and sock line or in flexural areas. Irritants in vapour or mist form are most likely to affect the face and neck.
Both direct contact dermatitis and allergic dermatitis produce similar changes in the skin and may present with:

· Redness of skin

· Vesicles or papules on affected area

· Crusting and scaling of skin

· Itching of affected area

· Fissures (chronic exposure)

· Hyperpigmentation (chronic exposure)

· Pain or burning sensation from affected area

Differential diagnosis

Contact dermatitis can be very similar in appearance to endogenous eczema, and it is important to assess the distribution of the skin lesions when arriving at a diagnosis. Other problems to cause confusion include psoriasis and ringworm. Pre-existing skin disease does not exclude occupational dermatitis too, indeed it may make the individual more susceptible.

Allergic and irritant contact dermatitis look identical.

Investigations

In most cases no investigations will be required and the diagnosis is made on the clinical findings and history.

Skin patch testing is occasionally performed using standardised allergens. It must be carried out meticulously. Excessive concentration or dilution of a test patch may cause false positives or false negatives. It can help to distinguish between allergy, irritation and endogenous eczema.

Associated diseases

The following may result from contact with chemicals:

· Contact dermatitis

· Contact urticaria

· Acne, especially with oils

· Pigmentary disorders

· Skin cancer, usually squamous cell carcinoma, are more common than usually recognised. ³

Management

Non-drug

The most effective form of management is to avoid the irritant producing the dermatitis, when this has been identified. The use of protective gloves or clothing may be helpful depending on the irritant and the environment. Patients should be advised to wash their hands using products without perfume, and dry thoroughly afterwards. Rings should be removed, thoroughly cleaned and not worn again until the condition has resolved. Avoidance of the irritant may be the only treatment required in milder cases of recent origin, the dermatitis will then resolve in a period of approximately three weeks. Simple emollients may be used if the skin barrier has not been breached. The usefulness of barrier creams remains controversial.

Drugs

More severe or chronic forms of dermatitis will benefit from the use of topical cortico-steroid cream, the strength and period of use of the steroid being adjusted according to the severity of the condition. The use of antihistamines may be helpful if itching of the affected area is a problem.

Second line agents e.g. PUVA, ciclosporin and azathioprine may be initiated in a specialist setting for the treatment of chronic, steroid resistant dermatitis.

Дата добавления: 2015-10-30