Methemoglobinemia

From Dog

Methemoglobinemia is a genetic disease of dogs characterized by increased circulating methemoglobin.

This condition can be caused by:

Methemoglobinemia causes reduced oxygen carrying capacity of the blood because methemoglobin cannot bind oxygen. If methemoglobin content reaches high values (> 50% of total hemoglobin), various organs may suffer hypoxic injury.

Methemoglobin reductase has been recognized in the Beagle[1], Chihuahua, Borzoi, English Setter, Poodle, Corgi and Pomeranian[2].

Clinically affected dogs usually present as puppies with cyanosis, reduced exercise intolerance, lethargy, tachycardia, tachypnea, ataxia, episodic stupor and syncope after brief exercise[3].

Diagnosis is based on enzyme assays for assessment of methemoglobin reductase enzyme levels[4].

A differential diagnosis would include acetaminophen toxicity, phosphofructokinase deficiency, pyruvate kinase deficiency and glucose-6-phosphate deficiency.

Emergency treatment of affected dogs may require methylene blue, given slowly over several minutes as a 1% solution (1 mg/kg IV). A dramatic response should occur during the first 30 minutes after treatment.

Some dogs can lead a reasonable quality of life with this condition while others deteriorate and require euthanasia.

References

  1. Srivastava S et al (2002) Methemoglobin reductase activity and in vitro sensitivity towards oxidant induced methemoglobinemia in swiss mice and beagle dogs erythrocytes. Mol Cell Biochem 232(1-2):81-85
  2. Fine DM et al (1999) Cyanosis and congenital methemoglobinemia in a puppy. J Am Anim Hosp Assoc 35(1):33-35
  3. Harvey JW et al (1974) Methemoglobin reductase deficiency in a dog. J Am Vet Med Assoc 164(10):1030-1033
  4. Harvey JW (1996) Congenital erythrocyte enzyme deficiencies. Vet Clin North Am Small Anim Pract 26(5):1003-1011