A young man who started losing his vision and even suddenly became color blind turned out to have an unusual cause for the problems: thallium poisoning.  

Thallium is a metal that can be absorbed through a person's skin and can lead to neurological problems. It does so because it takes the place of the similar chemical potassium in a number of processes in the body, particularly in the nervous system. Thallium poisoning can cause nerve pain, confusion and loss of muscle control, and the heavy metal can be fatal in high doses, according to the report of the young man's case.

But thallium is not included in standard tests for heavy metals in the body, and it wasn't until the doctors learned that the man worked in a chemistry laboratory that they thought to test for the element. [In Photos: The Power of Poison Through Time]

The patient "had all the hallmark signs" of thallium poisoning, said Dr. Enchun Liu, a ophthalmologist at the Retina Institute in St. Louis, Missouri, who treated the man for his vision problems and was the lead author of the case report, published Sept. 24 in JAMA Ophthalmology.

"This was the first case of thallium poisoning I've ever seen," Liu told Live Science. "As far as I know, it is a pretty rare condition."

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The man first went to the emergency room in December 2014 because of stomach pain, nausea and diarrhea, Liu said. Healthcare workers there gave the man intravenous fluids, diagnosed him with gastroenteritis (also known as stomach flu) and sent him home, Liu said.

Gastroenteritis symptoms are the first phase of thallium poisoning, and occur within 8 to 12 hours of exposure. Liu said he doesn't fault the ER for diagnosing the man with gastroenteritis, "because that would be a logical conclusion at that point."

However, after that diagnosis, in January 2015, the man returned to the hospital with vomiting, diarrhea, confusion and short-term memory loss, according to the report. His hair was falling out, and he had a rash across his face. The doctors ran tests, and ruled out conditions such as syphilis and tick-borne disease, Liu said.

Confusion and short-term memory loss are part of the second phase of thallium poisoning, and hair loss and facial rashes occur in the third phase, Liu said. One of the enzymes that thallium affects is particularly important in nerve conduction, he said. "That's why the neurologic system is usually the hardest hit," he said.

It wasn't until the patient's 10th day in the hospital that a neurologist thought to check the individual's thallium levels, given that the young man worked in a chemistry lab, Liu said.

"Thallium poisoning has a multitude of symptoms that affect many different organ systems and sometimes could be easily missed" when a patient first comes in, Liu told Live Science.

In addition, standard urine tests for heavy metals include only arsenic, mercury and lead, and this may have delayed diagnosis, he said.

The patient was treated with a dye called Prussian blue, which was originally developed for use in paints and ink, Liu said. In the digestive tract, the dye can get rid of certain metals by binding to them, which allows for the metals to be eliminated in the stool, he said.

After one week of Prussian blue therapy, the patient's blood thallium levels had dropped from over 100 micrograms per liter down to 25 micrograms per liter (the safe limit is 5 micrograms per liter), according to the case report.

"Most of the symptoms improve once [the] thallium is eliminated from the body, but residual permanent nerve damage does occur," Liu said. In the patient's case, the nerve damage causing vision loss and color blindness was what led him to Liu's clinic in February of this year, after he was treated for thallium poisoning and discharged from the hospital.

Liu last saw the young man in May of this year. While the patient's hair had grown back by that point, he still had some damage to his vision, which is likely permanent, Liu said. The man's recent blood thallium level was zero, Liu said.

Still, one mystery remains: exactly how the young man was exposed to thallium in his lab.

According to the case report, "no other students or faculty were affected, and the thallium was sealed without evidence of tampering." 

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