Thallium poisoning results from toxic exposure to this heavy metal, which is odorless, colorless, and tasteless. The toxicity of this metal results in neurologic, ocular, dermatologic, and gastrointestinal damage. Toxic doses may be ingested, absorbed through the skin, or inhaled as contaminated dust.
Thallium is an ingredient of rodenticides and insecticides. The metal as an ingredient was banned from the United States in the 1960s, but it is still commonly used overseas. Thallium was also a component of older pharmacologic agents used to treat diseases such as ringworm and syphilis, and trace amounts of the metal may still be found in costume jewelry, recreational drugs, radiographic contrast agents (thallium-201) to assess cardiac function, semiconductors, fireworks, and various other products.
Thallium poisoning may be acute, subacute, or chronic in nature. The acute form, which is most common, develops rapidly and is the result of short exposures to high doses. The timeline of symptoms following thallium poisoning is as follows:
Gastrointestinal / renal – Symptoms develop within 1-5 days of ingestion and include vomiting, diarrhea, abdominal pain, stomatitis, and liver and kidney dysfunction.
Neurologic – Symptoms develop from 2 days post-ingestion onward and include burning paresthesias (distal > proximal) and motor weakness. The neuropathies are progressive and often involve cranial nerves. Respiratory paralysis, nystagmus, ophthalmoplegia, and visual loss may develop.
Dermatologic – Symptoms develop from 15 days onward and include alopecia, Mees' lines on the nails, scaling of palmoplantar surfaces, and acne-like lesions. The alopecia is most significant on the scalp but may also involve the lateral eyebrows.
Chronic thallium poisoning is rare and usually results from a low level of exposure sustained over a prolonged duration. Usually only neuropathy develops in these patients.
When appropriate treatment is initiated, patients may experience significant recovery from the effects of thallium poisoning. In some patients, resultant paresthesias may not fully resolve, even with treatment.
Codes
ICD10CM: T56.811A – Toxic effect of thallium, accidental, initial encounter
SNOMEDCT: 51040009 – Thallium poisoning
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Differential Diagnosis & Pitfalls
The differential diagnosis for thallium poisoning includes:
Guillain-Barré syndrome – A distinguishing feature of thallium poisoning over Guillain-Barré syndrome is that there will be little to no loss of deep tendon reflexes in thallium poisoning. Additionally, the gastrointestinal symptoms are usually among the first manifestations of thallium poisoning and are not as common in Guillain-Barré syndrome.
Acne – While the facial eruption of thallium poisoning is acneiform, simple acne would not result in neurological or gastrointestinal symptoms.
Alopecia areata, favus, or other causes of hair loss – Hair loss in thallium poisoning would not respond to antifungals or anti-inflammatory agents, and other causes of hair loss would not be typically associated with neurological or gastrointestinal illness.
Arsenic poisoning – Arsenic poisoning is difficult to distinguish from thallium poisoning, as both conditions have alopecia and may have Mees' lines. Blood tests for each metal can clarify the diagnosis.
In the acute setting, the differential also includes:
Lead poisoning – Blood lead levels are not elevated in thallium poisoning.
Carbon monoxide poisoning – Carboxyhemoglobin levels and pulse oximeter levels are normal in thallium poisoning.
Organophosphate poisoning – RBC cholinesterase and plasma pseudocholinesterase levels are normal in thallium poisoning.
Diabetic neuropathy – This typically does not have sudden onset, and blood glucose and hemoglobin A1c levels will be abnormal.
Porphyria – Whole blood and urine porphyrin levels are normal in thallium poisoning.
