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Poisoning by subcutaneous metallic mercury is rare and usually accidental. Although it does not carry the same risks as mercury-vapour intoxication, it may still cause destructive early and late local reactions. Two deaths resulting from subcutaneous mercury injection have been reported in the literature. We present a case of accidental subcutaneous injection of mercury in the hand and discuss its management with a review of the literature.
Poisoning by metallic mercury is rare and usually accidental. It has been reported where mercury is used as a seal in a gas-analysis syringe, following puncture from broken thermometers, following occupational exposure and after rupture of the mercury-filled bulb of an intestinal tube. Other reported cases involve injection of the skin with mercury-containing preparations or tattooing.
Subcutaneous injection of metallic mercury has been reported as a self-inflected injury during attempted suicide, as part of drug addiction and in cases of psychiatric illness. Additionally, mercury has been subcutaneously injected in the belief that ‘quicksilver’ would enhance physical strength.
A 37-year-old right-handed self-employed thatcher accidentally struck the back of his left hand on straw that had been coated with a mixture of compounds containing mercury in order to render it fire-resistant.
The patient sustained a superficial skin laceration about half-an-inch long on the back of his left hand, which he dressed himself, and did not seek medical advice at that time.
The patient subsequently developed an area of redness and blistering over the wound, which progressed to abscess formation. He presented to the Accident and Emergency Department and was initially treated conservatively with oral antibiotics. The cellulitis failed to resolve, and he was referred to our unit 2 weeks after the initial injury.
The patient presented with swelling and tenderness over the second metacarpophalangeal joint of the left hand, resulting in some limitation of joint flexion (Fig. 1) .
Figure 1Swelling over the second left metacarpophalangeal joint.
On admission, a radiograph showed significant volumes of radio-opaque metallic foreign material in the soft tissues of the dorsum of the left hand (Fig. 2) . Further enquires into the nature of the compound with which the patient had fire-proofed the thatched roof raised the possibility of subcutaneous metallic mercury injection of the hand.
Figure 2Preoperative radiographs: (A) dorsal view and (B) lateral view.
The blood mercury level was found to be 120 nmol l−1 (normal values <30.0 nmol l−1), which confirmed the diagnosis of metallic mercury poisoning.
Apart from feeling a little tired, the patient did not show any general or neurological symptoms of mercury intoxication.
In view of the potential seriousness of mercury intoxication if not properly treated, and in light of the elevated blood mercury levels, we decided on early excision of the subcutaneous mercury.
A medially based skin flap was raised, and the mercury was found to be deposited throughout the tissue planes, surrounded by scarring and soft-tissue reaction. The layers in which the mercury had been deposited were excised (Figure 3, Figure 4) .
Figure 3A skin flap raised, revealing a mercury granuloma.
Histological examination of the removed tissues showed extensive fibrosis and foci of chronic inflammation, together with numerous foci containing globules of black foreign material surrounded by a foreign-body reaction consisting of histiocytes, foreign-body giant cells and collections of polymorphs. The nature of this black foreign material was not apparent on haematoxylin and eosin sections, but the possibility that it was mercury could not be excluded histologically, and correlation with the clinical history and the blood results confirmed the diagnosis.
The wound healed slowly over 3 weeks. The patient regained full function, resuming normal daily activities, and quickly returned to work. Postoperative radiographs confirmed the removal of a substantial amount of the deposited mercury, with only minimal radio-opaque traces seen (Fig. 5) .
Figure 5Postoperative radiographs: (A) dorsal view and (B) lateral view.
Blood mercury levels 1 month and 2 months after excision were 66 and 26.8 nmol l−1, respectively.
The patient had not developed any general symptoms of mercury intoxication at review 1 year following injury.
2. Discussion
Cinnabar (HgS) is the most important commercial ore of mercury. This metal is used in electrical apparatus, for industrial control instruments and in electrolytic cells for preparing chlorine and sodium hydroxide. Mercury compounds are used in antifouling and fire-resistant paints, as catalysts for amalgamation, as agricultural poisons and in general laboratory use. Medicinal uses include dental preparations, mercurial diuretics and dermal preparations for antisepsis and, prior to the advent of antibiotics, the treatment of syphilis. Mercury compounds have also been used as preservatives in cosmetics.
The potential toxic effects of mercury depend on the route of exposure. Inhalation of mercury vapour may result in weakness, fever and dyspnoea, which can progress to respiratory failure and death. Further, systemic mercury toxicity may develop, characterised by neurological, pulmonary and gastrointestinal disturbances. The major risk of intravenous administration of metallic mercury is embolisation, although some systemic absorption may occur. The effects of subcutaneous deposition and gastrointestinal-tract exposure are largely local and carry the lowest risks of systemic mercury poisoning.
Metallic mercury, once absorbed by the body, oxidises to mercurous (Hg+) and mercuric (Hg++) forms. Once mercuric salts are formed within tissues or in the blood stream, they are rapidly distributed throughout the visceral organs. The greatest concentrations of mercury are located in the kidneys, spleen and liver.
Although subcutaneous deposition of mercury does not carry the systemic risk associated with mercury-vapour inhalation, two deaths have been reported in the literature as a result of subcutaneous injection; these were secondary to renal failure and pulmonary empyema.
The tissue reaction following subcutaneous mercury injection, includes early and late reaction patterns. Early reactions include necrosis, acute inflammatory reactions and aseptic-abscess formation. Late reactions include foreign-body giant cell reaction, fibrosis, granuloma formation and membranous fat necrosis.
When mercury is subcutaneously injected, it is essential to prevent systemic absorption of the mercury and to treat the local effects properly.
The recommendations of Krohn et al for the management of subcutaneously injected metallic mercury are: first, prompt excision of all readily accessible subcutaneous areas in which mercury is located, irrespective of any symptoms of systemic toxicity; second, monitoring of central nervous system and renal functions for evidence of systemic toxicity; third, chelation therapy when there are systemic effects; and fourth, psychiatric consultation and treatment when indicated.
In conclusion, we recommend early surgical excision of injected-subcutaneous-mercury granulomas as this effectively lowers mercury blood levels and controls the local inflammatory reaction.
We consider early debridement, preferably in the operating theatre, necessary. Radiographs are useful after surgery to confirm the extent of removal.
Postoperative monitoring should ideally continue for 2 years and should include clinical examination for regional lymphadenopathy and biochemical analysis of blood mercury levels.
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