Yam bean seed poisoning mimicking cyanide intoxication

Yam bean is a common food in southern Taiwan. However, its seeds are rarely consumed. We describe five patients of yam bean seed poisoning in Taiwan, one of them life-threatening.

The five patients presented with perioral numbness, nausea and vomiting after eating a same soup made from yam bean seeds. One of them, a 54-year-old woman, had difficulty breathing and lost consciousness. Physical examination showed dilated pupils and coma with no focal neurological signs. The initial blood pressure was normal. Laboratory data showed a severe anion gap metabolic acidosis, with a serum lactate level of 185 mg/dL. An initial diagnosis of cyanide intoxication was considered and she was given sodium nitrite and sodium thiosulfate i.v. Hypotension ensued shortly afterwards and pulmonary artery catheterization showed a decreased cardiac index. Aggressive fluid and inotropic therapy were given and the patient eventually recovered. The other four patients suffered only minor gastrointestinal and neurological symptoms and received supportive treatment. Cyanide levels were negative in all five patients.

Yam bean seed poisoning can cause acute metabolic acidosis and altered mental status, which could be confused with acute cyanide intoxication from a cyanogenic glycoside-containing plant. To our knowledge, this is the first outbreak of yam bean seed poisoning reported in the English published work.