ContentsSynopsisCodesLook ForDiagnostic PearlsDifferential Diagnosis & PitfallsBest TestsManagement PearlsTherapyDrug Reaction DataReferencesView all Images (3)
Emergency: requires immediate attention
Methemoglobinemia
Other Resources UpToDate PubMed
Emergency: requires immediate attention

Methemoglobinemia

Contributors: Nina Haghi MD, David Sullo MD, Eric Ingerowski MD, FAAP
Other Resources UpToDate PubMed

Synopsis

Methemoglobinemia is a condition in which the oxygen-carrying capacity of circulating hemoglobin is diminished, causing a functional anemia. This occurs when the iron molecule of the hemoglobin complex remains in an oxidized state and can't reversibly bind oxygen. There are two types of methemoglobinemia: congenital and acquired.

The congenital type is due to a deficiency of the enzyme NADH-cytochrome b5 reductase, which impairs the ability of hemoglobin to bind oxygen, leading to poor oxygenation of body tissues. Cyanosis and hypoxia result. Congenital methemoglobinemia is further subcategorized into erythrocyte type (type 1) and generalized type (type 2). In type 1 disease, the enzyme is deficient only in erythrocytes, which accounts for up to 80% of the congenital methemoglobinemias. Cyanosis and mild polycythemia are the only symptoms. In type 2 disease, the membrane-bound form of the enzyme is deficient, causing deficiency in all tissues, manifesting with severe developmental abnormalities, severe intellectual disability, neurologic impairment, and premature death, usually in the first year of life.

Acquired methemoglobinemia is the more common type and is usually caused by ingestion of or exposure to oxidizing agents that oxidize hemoglobin directly to methemoglobin, or to the free radical O2-, which in turn oxidizes hemoglobin to methemoglobin. Some drugs / toxins that cause methemoglobinemia include (but are not limited to) benzocaine, prilocaine, dapsone, nitric oxide, phenytoin, rifampin, silver nitrate, sulfasalazine, aniline, and aniline dyes, among others. Classic examples include patients exposed to benzocaine in the endoscopy suite and infants exposed to nitrite from well water. Of note, nitric oxide is produced at higher levels in patients with sepsis and therefore causes elevated levels of methemoglobin.

In addition to cyanosis and hypoxia, other signs and symptoms of methemoglobinemia include neurological changes (hyperkinetic movements, seizures, or quadriparesis), microcephaly, mental deficiency, poor feeding, and failure to thrive. It can be life threatening or lead to greatly reduced functionality and shortened life expectancy.

Codes

ICD10CM:
D74.9 – Methemoglobinemia, unspecified

SNOMEDCT:
38959009 – Methemoglobinemia

Look For

Subscription Required

Diagnostic Pearls

Subscription Required

Differential Diagnosis & Pitfalls

Best Tests

Subscription Required

Management Pearls

Subscription Required

Therapy

Subscription Required

Drug Reaction Data

Below is a list of drugs with literature evidence indicating an adverse association with this diagnosis. The list is continually updated through ongoing research and new medication approvals. Click on Citations to sort by number of citations or click on Medication to sort the medications alphabetically.

Subscription Required

References

Subscription Required

Last Reviewed:10/30/2019
Last Updated:11/17/2019
Copyright © 2021 VisualDx®. All rights reserved.
Emergency: requires immediate attention
Methemoglobinemia
Methemoglobinemia (Hereditary Methemoglobinemia Type I) : Fatigue, Headache, Cyanosis, Exertional dyspnea, Present at birth
Copyright © 2021 VisualDx®. All rights reserved.