Which physical findings are characteristic of methemoglobinemia?

Updated: Dec 09, 2018
  • Author: Mary Denshaw-Burke, MD, FACP; Chief Editor: Emmanuel C Besa, MD  more...
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Answer

Physical findings may include the following:

  • Discoloration of the skin, mucous membranes, and blood (the most striking physical finding)

  • Cyanosis - This occurs with the presence of greater than 1.5 g/dL of methemoglobin (compared with 5 g/dL of deoxygenated hemoglobin)

  • Pallor of the skin or conjunctiva suggests anemia (and possible hemolysis), which can mask cyanosis if significant.

  • Seizures

  • Coma

  • Cardiac dysrhythmias (eg, bradyarrhythmia or ventricular dysrhythmia)

  • Acidosis

  • Symptoms associated with cardiac and/or neurologic ischemia

Skeletal abnormalities and mental retardation are associated with certain types of methemoglobin reductase enzyme deficiencies.

Methemoglobin levels as high as 20% are typically tolerated with no clinical symptoms, whereas higher levels (30-40%) may be associated with headaches and dyspnea, especially upon exertion.

Patients with hereditary methemoglobinemia are commonly described as being more blue than sick. They appear cyanotic with a diffuse slate-gray appearance. Cyanosis is easily observed on the nose, cheeks, fingers, toes, and in the mucous membranes, including the fundi, and may go unrecognized for a long time in patients with more heavily pigmented skin or in patients with moderate-to-severe anemia. Clubbing is absent.

Patients with hemoglobin M disease with the alpha chain variant can present at birth with cyanosis, whereas patients with the beta chain variants present in the latter half of infancy.

Chaurasia and colleagues reported corneal epitheliopathy in four patients with congenital methemoglobinemia. They observed dark-colored conjunctival vessels and recurrent corneal epitheliopathy in three girls and one boy from two affected families. The corneal lesions resolved within 2 to 3 weeks with supportive therapy and vitamin C supplements. [57]


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