Monday, June 11, 2012

Mercury rising

A patient who had been working in a recycling company that handled thermometers presented with fever, dry cough, fatigue and rash. Based on imaging (CXR showed massive radio-opaque material in the lungs, right atrium and right ventricle; skeletal survey showed radio-opaque deposits in the kidneys, bowel wall, and bladder wall), symptoms, and a positive history of exposure, a diagnosis of mercury intoxication was made. The patient developed multi-organ failure including anuric acute renal failure, and nephrology was consulted. Further background details on the case can be found here. What is the treatment and the role of dialysis in mercury intoxication? 

Metallic mercury has a widespread use both within industry and in many everyday objects such as thermometers, dental amalgams, batteries, fluorescent light bulbs, and many others. Mercury intoxication can result from vapor inhalation, resulting in severe respiratory symptoms, or from injection, usually in cases of attempted suicide. 

The chelating agents 2,3- dimercaptopropanesulfonic acid (DMPS) and meso-2,3-dimercaptosuccinic acid (DMSA) are central to the management of mercury toxicity. DMSA is given orally, and can cause leucopenia and elevated liver enzymes. DMPS is an intravenous medication and its use is associated with hypotension. In our patient, DMSA 500 mg po q 8hrs was given for 4 days, before it was discontinued because of elevated LFTs and leucopenia. We then started DMPS with CRRT but unfortunately, after two weeks of supportive treatment, the patient died. 

Chelators such as DMPS and DMSA work by mobilizing mercury and facilitating its excretion through the kidneys. This creates a management conundrum in the anuric patient, as this route of excretion is not available. Consistent with this, our patient’s blood mercury levels rose dramatically during chelator treatment, despite CRRT. We hypothesize that the administration of DMPS mobilized mercury from extracellular deposits and redistributed it to the blood and organs, but it failed to be adequately eliminated from the body because of anuria. For this reason, intensive CRRT with a high-flux dialyzer is a critical adjunct to chelator therapy. If this is not available, continuous renal replacement therapy with chelators have showed better mercury clearance than conventional dialysis, whereas peritoneal dialysis has been shown to be ineffective at clearing mercury. These principles should be borne in mind in other heavy metal poisonings also. Other management pearls I took from this unusual case were to initiate dialysis early and to give DMSA at a lower and more frequent dose to avoid serious side effects. 

Tarek Alhamad M.D.

No comments: