In the 1994 Centers for Disease Control and Prevention definition of chronic fatigue syndrome, the agency stated that although many diseases need to be ruled out when attempting to diagnose chronic fatigue, chronic fatigue syndrome should be diagnosed if a detailed clinical assessment shows that symptoms conform to a chronic fatigue definition even if chronic fatigue syndrome criterion are not met.6)
According to reports, the causes of chronic fatigue can be identified in two-thirds of patients with chronic fatigue; 46% of these patients were diagnosed with characteristic organic diseases related to fatigue.7)
Fish consumption continues to increase in Korea as people avoid consuming meat due to the mad cow disease crisis and avian influenza; people assume that fish is safer than other meats. This increased consumption implies that the dangers of methyl-mercury accumulation and toxicity may be increasing. Therefore, as suggested in the educational reports on the diagnosis and treatment of chronic fatigue, any possibility of exposure to toxic materials must be explored.8)
Mercury can be categorized as elemental, inorganic, and organic.9)
Unlike elemental and inorganic mercury, which mainly are absorbed through the lungs and skin, 95% of organic mercury is quickly absorbed by the digestive organs. Phenyl mercury, one type of organic mercury, is usually contained in spermicides and fungicides, but these compounds are no longer used. Ethyl-mercury, another type of organic mercury, is found in thimerosal, a vaccine preservative, but the extent to which thimerosal can harm humans remains controversial. Methyl-mercury, the most common organic mercury, is accumulated through the food chains of the ecosystem. It is found in fish, crustaceans, and marine mammals and is more highly concentrated in carnivorous fish with longer life spans. Consumption of seafood such as fish is the primary source of exposure to organic mercury.10
Absorbed methyl-mercury is conjugated with cysteine, which is an amino acid that is abundant in inner-body proteins. The methyl mercury-cysteine conjugation penetrates the inside of a cell through the amino-acid transporter and is accumulated there. It also easily travels through the blood-brain barrier. Consequently, the conjugation is oxygenated and accumulated, which is toxic to humans and is called the chronic exposure of methyl-mercury.14
Symptoms resulting from chronic exposure to methyl-mercury gradually develop and may be observed after a long period of time. The main damage occurs in the nervous system and symptoms include fatigue, decay, headache, poor concentration, and mental disorders.17)
Among mercury-exposure diagnostic methods, blood tests are useful to detect acute exposure; urine tests, to detect chronic exposure to elemental or inorganic mercury; and HTMA, to detect chronic exposure to organic mercury (methyl-mercury).3)
The first priority when treating mercury exposure is to block source of exposure to organic mercury. In the case of acute exposure, a chelating agent can be directly injected into the blood. However, in cases of chronic exposure, because mercury has infiltrated the organs rather than the blood, it is helpful to promote a synthetic reaction within the organs which can chelate the heavy metal. Metallothionein is one such material that and removes heavy metals, and its synthesis is promoted by zinc.18)
In our patient, we administered specific heavy metal removal medication containing zinc and cysteine to chelate and remove the mercury.
A research series reported a positive connection between the concentration level of methyl-mercury in the hair and frequency of fish consumption.19
However, whether a low level of methyl-mercury exposure from fish consumption is toxic to adults remains controversial.21)
In a study of pregnant women and fetuses with low levels of mercury exposure in the blood, methyl-mercury was found to infiltrate the placenta and blood-brain barrier and caused developmental disorders in fetal brains and nerves, but the exposure presented almost no effect in the pregnant women.22
Early symptoms of nerve intoxication from organic mercury exposure manifest at the level of 200 µg/L in a blood test, and 50 µg/g in a hair assay.24
In natives residing near the Amazon River, malfunction of the nervous system was observed at levels lower than intoxication from organic mercury exposure.27
In a study that considers the effect of low-level methyl mercury exposure on adult nervous-mental functions, the average mercury concentration of the subjects was 4.2 ± 2.4 µg/g. Depending upon the dose, mercury exposure caused distinctive changes in fine motor skill, dexterity, and concentration. Specific differences were found in fine motor speed (3.6 µg/g), digit symbol (3.8 µg/g), total logical memory (3.7 µg/g), backward digit span (3.6 µg/g), easy learning (3.7 µg/g), and the logical memory first-story test (3.7 µg/g).29)
In 2008, the World Health Organization provided a criterion to measure the dangers of methyl-mercury by fish consumption; the criterion was that mercury concentration exceeding 2 µg/g in the hair can be dangerous.30)
Likewise, many studies have been conducted to determine the accumulation of methyl-mercury in amounts lower than 50 µg/g.
It cannot be concluded that all chronic low-level organic mercury exposure (mercury concentration levels between 2 and 50 µg/g in the hair) will cause fatigue. Because it is difficult to identify factors that cause chronic fatigue other than low-level exposure to organic mercury via fish consumption, and because there is no response to conventional treatments for chronic fatigue, we believe that low-level exposure to organic mercury can cause chronic fatigue. It is difficult to conclude a causal relationship from our study as we have only described a single patient here. However, as our treatment was effective, it is clear that chronic idiopathic fatigue symptoms can improve after removing mercury from the body.