Methemoglobinemia natural history, complications and prognosis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Template:Aksiniya K. Stevasarova, M.D.
Overview
Congenital (Hereditary) Methemoglobinemia
There are three main congenital conditions that lead to methemoglobinemia:
1. Cytochrome b5 reductase deficiency and pyruvate kinase deficiency
2. G6PD deficiency
3. Presence of abnormal hemoglobin.
Acquired or Acute Methemoglobinemia
Some of the most common causes include different oxidant drugs, toxins and chemicals.
Natural History
Patients with hereditary forms of methemoglobinemia are generally asymptomatic, with the exception of having chronic cyanosis. Unfortunately, despite the benign nature of the congenital methemoglobinemia, people with type IIb5 cytochrome-reductase deficiency have poor prognosis and shorter lifespan, mainly due to neurologic complications.
In acquired methemoglobinemia, depending on the amount and duration of toxin exposure, the levels of MetHb in the blood will be different. As a result we expect different outcomes, which are as follows: MetHb of 15% presents with skin and blood color changes at levels; levels above 15% will result in hypoxia and levels above 70% can lead to death. [1] [2]
- ↑ {{Rev Bras Anestesiol. 2008 Nov-Dec;58(6):651-64. Methemoglobinemia: from diagnosis to treatment. [Article in English, Portuguese] do Nascimento TS1, Pereira RO, de Mello HL, Costa J. pmid=19082413}}
- ↑ {{Toxicol Rev. 2003;22(1):13-27. Occupational methaemoglobinaemia. Mechanisms of production, features, diagnosis and management including the use of methylene blue. Bradberry SM1. pmid=14579544}}
Complications
Death is the most serious complications of methemoglobinemia especially when MetHb levels approach 70%. In severely sick patients death may occur even with lower levels of MetHb. Other complications include myocardial infarction, seizure and coma. [1]
- ↑ {{Toxicol Rev. 2003;22(1):13-27. Occupational methaemoglobinaemia. Mechanisms of production, features, diagnosis and management including the use of methylene blue. Bradberry SM1. pmid=14579544}}
Prognosis
Depending on the anoxic end-organ damage caused by MetHb, the prognosiss varies between mild an fatal. [1]
- ↑ {{Rev Bras Anestesiol. 2008 Nov-Dec;58(6):651-64. Methemoglobinemia: from diagnosis to treatment. [Article in English, Portuguese] do Nascimento TS1, Pereira RO, de Mello HL, Costa J. pmid=19082413}}