Cyanosis and congenital methemoglobinemia in a puppy.

A six-month-old Pomeranian was referred for evaluation of cyanosis. The puppy had been cyanotic since it was acquired at six weeks of age, but otherwise appeared normal. Diagnostics were aimed at the most common causes (i.e., congenital defects in the cardiovascular and respiratory systems) of cyanosis in a juvenile animal. No clinically significant abnormalities were detected on evaluation of thoracic radiographs, echocardiogram, cardiac color-flow Doppler examination, or blood gases. At this point, a dysfunction in hemoglobin was considered as a possibility. Methemoglobinemia due to deficiency of methemoglobin reductase enzyme was diagnosed based on a specific assay.