The occupational limit for thallium exposure is 0.1 mg/m^3 to the skin per 8 hours a day. Levels of 15mg/m^3 are considered immediately dangerous to one’s health. Thallium (1) is readily absorbed through the skin as well as during inhalation. Due to thallium being tasteless, odorless, and water soluble, accidental and criminal intoxication have been reported.
Similar thallium salts were once used to treat dermatophytosis. Before the use of technetium-99m for nuclear medicine studies, thallium-201, a radioactive isotope, was the mainstay and is still used for stress tests evaluating coronary artery disease. (This type of thallium is more than 4000 times less potent.) Scintigraphy using thallium evaluates blood supply to tissue thallium uptake. Exercise or drugs used to vasodilate normal coronary arteries causes alteration of circulating blood, leading to a reduction of coronary blood circulation (coronary steal syndrome).
Thallium is a gray post-transition metal that is not found in free nature. Though similar to tin when isolated, Thallium discolors when exposed to air.
Patterns of Spread
In 1965 thallium was banned from United States households and, subsequently, banned commercially in 1975. Due to intoxication often mimicking other diseases, ill patients may go unnoticed. More current uses of thallium are in the semiconductor and optical industries. Thallium is used in rat poison and ant killer, and because it is both odorless and tasteless, it has become an accidental intoxication as well as a criminal poison in some cases. To this day thallium is seen in rodenticide and insecticide in other countries. In Africa, thallium has been used as a pesticide, which has led to food contamination. Chinese herbal medications also have been contaminated. Intoxication occurs by cumulative intake through the skin, respiratory, and gastrointestinal tracts. Accidental snorting by cocaine abusers, accidental injection by heroin uses, as well as skin absorption through protective gloves have been reported.
Within the United States, 29 single exposures, with only one major outcome and no deaths were reported in 2016 by the American Association of Poison Control Center. Internationally thallium toxicity is common in developing countries; however, little data is available.
Six percent to 15% has been reported for acute thallium toxicity.
Ten to 15 mg/kg is a lethal dose for humans. Death can still occur at lower dosages.
No data regarding age, sex, race is available.
Thallium is structurally similar to potassium and is treated as such at the cellular level. The following five major toxicologic effects are seen with thallium toxicity:
The three toxicokinetic phases of thallium are as follows:
Symptoms include gastrointestinal, neurological, and dermatological.
Results in continuation of the above; however, neurological symptoms persist even as blood thallium levels decrease.
Gastrointestinal symptoms (presenting early within 3-4 hours)
Neurologic symptoms (presenting later around 2-5 days post exposure)
At first nonspecific findings such as scaling and acneiform/pustular eruptions, may occur. After 2 to 3 weeks, alopecia begins due to the cysteine disulfide bond disruption. One month after poisoning Mees lines appear on the nails.
Patients may experience tachycardia, and/or hypertension.
Though the exam should focus on the affected areas, a neurologic, ophthalmologic, and gastrointestinal examination is crucial.
Only elevated thallium levels in hair, nails, blood, urine, feces, and saliva can make a definitive clinical diagnosis. A 24-hour urine thallium concentration, assayed by atomic absorption photospectrometry, is the standard method. Although a urine spot test is faster, it has a high false-positive rate. Blood thallium levels may be falsely negative. The following are other tests to order:
Thallium is radiopaque. Thallium may be reviled after ingestion.
Electrocardiograms should be ordered to evaluate for arrhythmias and tachycardia. An electroencephalogram should be ordered for any seizure-like activity as well as a nerve conduction study for patients experiencing neurological symptoms.
Much like many exposures, care starts with stabilization, airway, breathing, and circulation as well as removing contaminated clothing. Activated charcoal can be used for patients presenting within 1 hour of ingestion.
If the patient had dermal exposure, their skin is to be washed with soap and water. For eye exposure, irrigate the eyes with room temperature water. Activated charcoal and Prussian blue may be used for gastrointestinal ingestion. Prussian blue has been shown to be more successful and is approved by the United States Food and Drug Administration.
Differential of Other Toxicities
The sooner treatment is initiated the better the prognosis although chronic exposure may have a long recovery.
Neurological damage may be persistent. The feet and lower extremities have been most reported to be persistent. The following psychiatric symptoms also have been reported:
Patients who intentionally ingest thallium should have a psychiatric evaluation. All patients should have close follow up care.
The management of thallium toxicity is by a multidisciplinary team that includes an emergency department physician, poison control, internist, neurologist, and an intensivist. the initial management of a patient with thallium toxicity follows the trauma ABCDE protocol. Activated charcoal can be used for patients presenting within 1 hour of ingestion. If the patient had dermal exposure, their skin is to be washed with soap and water. For eye exposure, irrigate the eyes with room temperature water. Activated charcoal and Prussian blue may be used for gastrointestinal ingestion. Prussian blue has been shown to be more successful and is approved by the United States Food and Drug Administration. The prognosis for patients with thallium toxicity depends on the dose ingested and the presence of neurological symptoms. Those with minimal symptoms can fully recover with treatment but patients with severe toxicity may continue to have neuropsychiatric deficits for a long time. (Level V)
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