Methemoglobinemia

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Classification according to ICD-10
D74.- Methemoglobinemia
D74.0 Congenital methemoglobinemia
D74.8 Other methaemoglobinemia
D74.9 Methaemoglobinemia, unspecified
ICD-10 online (WHO version 2019)

In medicine, methaemoglobinemia is an increased concentration of methaemoglobin (Met-Hb) in the blood. The hemoglobin present in the red blood cells , which serves to transport oxygen, is converted into the non- functional methemoglobin ( oxidized , see methemoglobin) and is therefore no longer available for oxygen transport.

Symptoms

Chronic methemoglobinemia is often clinically silent. If the course is acute, the typical symptoms of an insufficient supply of oxygen to the tissue appear early on. These include headache, fatigue, shortness of breath and lethargy. From a Met-Hb concentration of more than ten percent of the total hemoglobin, hypoxemia (lack of oxygen in the blood) with cyanosis (blue discoloration of the skin and mucous membranes) occurs. The blood turns a brownish red color. In 15–20 percent, dizziness , nausea , headache , accelerated heart activity, shortness of breath and somnolence (drowsiness, sleepiness) occur. A concentration of more than 70 to 80 percent leads to death if left untreated .

causes

Methaemoglobinemia is mainly triggered by a defect in the hemoglobin or (in the case of congenital methaemoglobinemia ) a genetic cytochrome b5 reductase deficiency. Such hereditary enzyme defects are rare. The hemoglobin defect can either be hereditary or triggered by toxins. These substances oxidize the iron ion from Fe 2+ to Fe 3+ . From a chemical point of view, heme is a bio-organic complex compound and the increase in the oxidation level of the central atom (iron) has a massive effect on the properties of the complex and ultimately leads to a loss of function of the entire hemoglobin.

The oxidation can take place as a mono-oxidation or coupled. Since molecular oxygen can also oxidize the heme, part of the hemoglobin present in the erythrocytes is also present in the blood of healthy people as methemoglobin. However, the share here is less than one percent.

The oxidizing substances include some drugs ( phenacetin , quinine , lidocaine , benzocaine , prilocaine , metoclopramide , nitroglycerin , sulfonamides, etc.), nitrous gases , aromatic nitro and amino compounds ( poppers , herbicides ) and others. Infants are at risk from drinking water or vegetables with excessively high nitrate levels . The risk of anemia in infants is significantly higher due to lower enzyme activity.

diagnosis

If methaemoglobinaemia is suspected, a drop of patient venous blood can be placed on a filter paper. Since methemoglobin cannot be reduced by the oxygen in the air, it remains brown, while normal hemoglobin turns red when oxygen is absorbed from the room air. In this very simple test, a drop of normal blood is usually placed next to the patient's blood in order to have a direct comparison. In the blood smear, Heinz inner bodies in the erythrocytes, which represent the histological correlate of methemoglobin, are found. Since the methemoglobin molecules "clump" in the erythrocytes, so to speak, these precipitates arise. Methaemoglobinaemia can be detected in EDTA blood or heparin blood in the laboratory. A diagnosis by means of multi-wavelength pulse oximeters or a blood gas analysis is more precise . The methemoglobin can also be quantitatively detected spectroscopically .

therapy

No treatment is possible for hereditary causes. In the case of toxic methaemoglobinemia, the triggering substance must be discontinued. If necessary, methylene blue , toluidine blue or ascorbic acid can be administered. The intravenous short infusion (about 5 minutes) of methylene blue reduces the methaemoglobin content in the blood by activating the cytochrome b 5 reductases . The administration of these drugs is contraindicated in certain patients because they can exacerbate the anemia (for example, if there is a glucose-6-phosphate dehydrogenase deficiency). In the event of therapy failure, the only last resort is an exchange transfusion .

Occur

One known case in which a large group of people had methemoglobinemia was that of the Fugate family. This lived in the mountains of Kentucky and was commonly known as the blue fugates . Due to an extremely rare allele , they had methemoglobinemia, which turned their skin blue.

History of the blue fugates

The French immigrant Martin Fugate, an orphan, and his wife Elizabeth Smith, a native American, settled on the east bank of Troublesome Creek around 1820 near Hazard, Kentucky . Few other families also settled in this region, but since it was not accessible by roads, there was hardly any fluctuation in the population living there. Weddings within one's own family were not uncommon.

Martin and Elizabeth were both carriers of the recessive methemoglobinemia allele (met-H), so four of their seven children were born with blue skin. They suffered from methaemoglobinemia, which, moreover, did not cause any symptoms. In this way, the children were able to lead a largely untroubled life and later father offspring themselves. Since this also happened within the Fugates and there was generally little mixing of the gene pool, numerous blue people soon lived in the mountain village on Troublesome Creek.

However, after the first coal mines were built in the region in 1912, rails and later roads soon reached the region. Thus the isolation was broken and there was a greater mixing of the gene pool, so that people with blue skin became increasingly rare.

Nonetheless, a child named Ben Stacy, who was a distant relative of the Fugate clan, was born in 1975. The blue color of his skin was also clearly visible on him. But a few weeks after the birth, she disappeared again.

literature

Web links

Individual evidence

  1. ↑ Ernst Mutschler, Monika Schäfer-Korting: Textbook of Pharmacology and Toxicology . 8th, completely revised and expanded edition. Wissenschaftliche Verlagsgesellschaft, Stuttgart 2001, ISBN 3-8047-1763-2 , pp. 988f.
  2. ^ A b c d e E. Kochs, HA Adams, C. Spies: Anästhesiologie , 2nd, completely revised edition. Georg Thieme Publishing House. Stuttgart 2008. ISBN 978-3131148629 , p. 407.
  3. ↑ Klaus Aktories, Ulrich Förstermann among others: General and special pharmacology and toxicology. 11th edition. Urban & Fischer Verlag, 2013, p. 1016ff.
  4. ↑ G. Eisenbrand, M. Metzler: Toxicology for Chemists. Georg Thieme Verlag, Stuttgart 1994, ISBN 3-13-127001-2 , p. 77.
  5. ^ Lothar Thomas: Laboratory and Diagnosis: Indication and evaluation of laboratory results for medical diagnosis . TH-Books-Verl.-Ges., Frankfurt am Main 2008, ISBN 978-3-9805215-6-7 .
  6. ↑ M.Moos, R. Schröder, M. Lang, B. Frauchiger: Severe methaemoglobinemia - diagnosis, therapy and pathophysiology using the example of a case . In: Anästhesiol. Intensive med. Emergency med. Painful. , 2009 44 (5): pp. 328-334, doi : 10.1055 / s-0029-1224778
  7. ^ Blue-skinned family baffled science for 150 years. January 22, 2013, accessed May 10, 2018 .
  8. ↑ A mountain village full of people with blue skin - bluemind.tv . April 29, 2018 ( bluemind.tv [accessed May 10, 2018]).
  9. ^ Cathy Trost: The Blue People of Troublesome Creek. In: Science 82, November, 1982. Retrieved May 10, 2018 .
  10. ↑ ABC News: Genetics Solves Blue-Tinged Mystery. February 22, 2012, accessed May 10, 2018 .
  11. ^ Meet Ben Stacy, the living descendant of the BLUE men of Appalachia - who was born discolored too but grew out of it . In: Mail Online . ( dailymail.co.uk [accessed May 10, 2018]).