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Mercury exanthema is a pruriginous rash presenting as vermilion red or purplish maculopapular plaques appearing suddenly in the large folds a few hours after exposure to mercury, then extending in a diffuse, bilateral and symmetrical manner in 3-5 days and gradually disappearing without sequelae. The rash is most marked in the folds, especially the folds of the groin. Small amicrobic pustules often appear secondarily, 2 to 3 days after the start of the exanthema. On contact of the skin with a mercury derivative, localized contact dermatitis may be associated with the previously described lesions: pubic dermatitis (insecticide powder), foot dermatitis (plastic boots containing mercury chloride), periorbital dermatitis (eye cream)… There have been reports of extensive vesiculobullous forms predominantly in the folds, as well as erythema multiforme-like forms. Systemic symptoms are common (fever above 39°C, malaise, axillary and inguinal lymphadenopathy).
Mercury exanthema produces systemic contact dermatitis after inhalation of mercury vapours (breakage of a mercury thermometer in most cases), transcutaneous absorption or ingestion of a mercury derivative in a patient previously sensitized to mercury (by the application of skin antiseptics such as mercurochrome, for example).
Subjects should be questioned about exposure to a mercury derivative a few hours or days before the onset of the rash and about previously known contact allergy to mercury. Additional tests in the acute phase can show leukocytosis with or without hypereosinophilia, increased CRP, transient proteinuria and, inconstantly, high levels of mercury in the blood and urine. A skin biopsy will not show any specific signs. Patch tests carried out secondarily are more useful for the diagnosis if they are positive for mercury compounds. However, an estimated 3.6 to 2.8 percent of the general French population have positive skin tests for metallic mercury and thimerosal, respectively. Thus, a positive test is an important but not sufficient element for the diagnosis of mercury exanthema in the absence of clinical and anamnestic signs. It is strongly advised not to carry out provocation tests by inhalation of mercury vapour because of their dangerousness.
Treatment in the acute phase is based on avoidance of the allergen and symptomatic use of topical corticosteroids and antihistamines. A short course of systemic corticosteroids has sometimes been proposed in severe cases. Thereafter, all contact with mercury and its organic and inorganic compounds should be avoided (Table I).
Examples de products
Electrical industry (batteries, lamps, fluorescent tubes, rectifier, contactors)
Chemical industry (batteries, explosives, sodium chloride electrolysis)
Measuring instruments (thermometer ...)
Amalgams and dental alloys, jewellery…
Fungicides, germicides, herbicides, insecticides
Industry for some papers and felt-tip pens
Hair lotions, embalming fluids d’embaumement
— mercuric chloride (corrosive sublimate of mercury)
— mercurous chloride (calomel)
— mercury oxide (yellow, red)
Plastics, papers, waxes, eye ointments (mercuric oxide yellow 1 percent Chauvin®)
— red mercury sulphate (vermilion
— mercury sulphide
Phenyl mercuric salts (acetate, benzoate, nitrate, bromate)
Ophthalmic solutions (Dacryosérum®, Néoparyl B12®)
Paint, shoe liners
Thiomersal (thimerosal, merthiolate, ethylmercury thiosalicylate)
Antibacterial, antifungal, antiseptic (Dermachrome®)
Medical Products preservative:
— vaccines (Engerix B® vaccine, Ronchese VGR® influenza vaccine, Pasteur® tetanus vaccine, ImmuGrip®, Tétagrip 05®, Tétavax®, DT bis®, DT Coq®, DT Vax®, Vaxicoq®, Vaxigrip®, Fluvirine®, Mutagrip®, HB Vax DNA®)
— injectable immunoglobulins
— eye drops (Vitaseptol®, Collyrex®, Constrilia®, Fluorescéine Faure collyre®)
— ear or nose solutions (Rhinopten nébulisateur®)
— solutions for contact lenses (Polyclean®, Soaclens®)
— aqueous eosin
Preservative for makeup removal products and eye makeup
Mercurochrome (merbromin, disodium salt of 2,7-dibromo-4-hydroxy-mercuri-fluorescein)
Skin antiseptics (Pharmadose mercurescéine® compresses, Soluchrom®)
Skin antiseptics (Mercryl Laurylé®)
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