What is a classic sign of arsenic poisoning?

Mees lines are a classic sign of arsenic poisoning, characterized by white transverse lines that grow out with the nail and are indicative of previous illness or systemic toxicity. These lines can appear in patients who have suffered from arsenic exposure, as arsenic interferes with keratin synthesis and can lead to disturbances in nail formation.

The appearance of Mees lines typically becomes evident a few weeks after exposure and can persist long after the arsenic has been cleared from the body, thus serving as a useful marker for forensic pathologists when assessing cases of suspected arsenic poisoning.

Other manifestations of arsenic poisoning may include gastrointestinal symptoms like cramping abdominal pain or systemic effects such as headaches, but these are not the hallmark signs that specifically indicate arsenic. Hematemesis, or vomiting blood, can occur in various medical conditions including gastrointestinal hemorrhage, but it is not directly associated with arsenic poisoning. Therefore, Mees lines represent a more definitive and specific finding related to arsenic exposure.