A Case of Aniline Poisoning Manifesting as Cyanosis with Unknown Cause

A 38-year-old man was brought to the hospital for emergency treatment of cyanosis. The patient exhibited generalized cyanosis and impaired consciousness despite adequate oxygen therapy. Arterial blood was black, and arterial blood gas analysis revealed an abnormally high methemoglobin level of 67.8%. We later interviewed his colleagues regarding his exposure to aniline while working at the factory and diagnosed him with methemoglobinemia due to aniline poisoning. The patient was administered methylene blue (MB) after being transferred to another hospital, where this treatment was available, resulting in an improvement in symptoms. Although rare, methemoglobinemia is serious. A good understanding of the circumstances at disease onset, characteristic findings, and abnormal values of methemoglobinemia is important. In addition, MB is an important therapeutic for the treatment of methemoglobinemia; if MB is not available at a particular hospital, transfer of the patient to a hospital that stocks MB should be considered.