Methemoglobinemias are characterized by the increased content in blood of level of the methemoglobin representing one of forms of the oxidized hemoglobin.
Epidemiology Hereditary methemoglobinemias are extended among inhabitants of Greenland, Indians of Alaska and representatives of the tribe navakhos (USA), sporadic cases of this pathology are described in the countries of Europe and Asia. In our country it is found in aboriginals of Yakutia, isolated cases — in other territories. About prevalence acquired methemoglobinemias, meeting more often among children, it is not enough data.
Etiology and pathogeny In erythrocytes there is a complex of the factors participating in recovery of a methemoglobin in hemoglobin among which an important role is played by a methemoglobin reductase. At healthy faces the methemoglobin is formed always, but in insignificant quantity (0,1 — 1%) under the influence of the okislyashchy substances appearing as a result of a metabolism. At some diseases (lungs, hearts) the quantity it can reach 3 — 4%. The methemoglobin unlike oxyhemoglobin contains trivalent iron, with firmness contacts oxygen in lungs and does not give it to fabrics that causes development of a fabric hypoxia.
Sometimes substances of the oxidizing action (aniline paints, antipyrine, amylnitrate, bertoletovy salt, hydrochinone, glycerin, arsenous hydrogen, PASK, streptocides, acetphenetidiene, furadonin, quinine, chloramphenicol, etc.), getting into erythrocytes, turn hemoglobin into a methemoglobin. The medicines possessing the oxidizing property at long appointment or even a single dose in a therapeutic dose can lead to increase in blood of quantity of a methemoglobin and to development of a methemoglobinemia. The similar phenomenon is observed at the children aged before half a year having easily oxidized fetalis hemoglobin, at persons with enzymatic insufficiency in erythrocytes or having the corresponding abnormal hemoglobin (NBM).
Classification. Distinguish the hereditary and acquired disease forms from a methemoglobinemia.
Approximate formulation of the diagnosis: 1. NBA— a hereditary methemoglobinemia at homozygotes with the expressed constant cyanosis in the field of a nasolabial triangle, a conjunctiva, nails and a mucous oral cavity with lag signs in development (physical and mental). 2. The acquired methemoglobinemia proceeding with short-term cyanosis of nails, mucous oral cavity, nasolabial triangle and other localization.
Clinic The NBA-methemoglobinemia is inherited on autosomal recessively type. The homozygous form of a disease is clinically shown by cyanosis of area of a nasolabial triangle, a mucous membrane of an oral cavity, conjunctiva and nails. This leading symptom of a disease" appearing right after the child's birth, remains during all life. Patients are often disturbed by headaches, dizziness, short wind, tachycardia, fast fatigue, drowsiness, and also lag signs in physical and mental development. Increase of maintenance of a methemoglobin (15 — 40%) and quantities of erythrocytes (a compensatory hyperglobulia) is found.
At a heterozygous form there are no clinical displays of a disease, in erythrocytes decrease in a methemoglobin reductase comes to light (to 50%). At reception of metgemoglobinoobrazuyushchy drugs cyanosis, a resistant hyperglobulia develops, methemoglobin level increases, blood gains chocolate-brown color and sharply activity of a methemoglobin reductase decreases.
The hereditary NBM-methemoglobinemia is characterized by availability of the abnormal hemoglobin of the same name (5 molecular HbM options are known now).
HbM - a methemoglobinemia is inherited on autosomal dominantly type. At a heterozygous form of a disease the maintenance of HbM can be normal (not higher than 1%); at effect of substances oxidizers the HbM level reaches high figures (to 20%). Blood of patients gains chocolate-brown color, hematologic indicators remain normal.
The acquired methemoglobinemias meet more often among children when the oxidizing chemicals and drugs in the absence of deficit of a methemoglobin reductase, and HbM cause increase in quantity of a methemoglobin. Cyanosis which comes to light after penetration into an organism of the toxic or oxidizing substances and remains not for long is characteristic of this form of a methemoglobinemia (to 2 days). Blood of patients gains chocolate-brown color. The quantity of a methemoglobin is increased, its maximum spectroscopic absorption — at the wavelength of 630 mm. In erythrocytes it is found Heinz's little bodies.
Sulfhemoglobinemias meet much less often than a methemoglobinemia. Sulfhemoglobin is a product of oxidatic transformation of hemoglobin. Normal it is absent in erythrocytes or contents does not exceed it 0,1%. Increase in the general hemoglobin at the expense of the sulfhemoglobin which is not possessing function of transport of oxygen leads to difficulty of intake of oxygen in fabric. The increased formation of sulfhemoglobin can happen under the influence of streptocides, acetphenetidiene, aromatic connections and other medicines.
The main symptoms of a disease are cyanosis (within 3 — 4 months, i.e. until the end of life of population of the erythrocytes containing sulfhemoglobin), blood coloring change, signs of an increased hemolysis. These displays of an illness are always accompanied by the general weakness, dizziness, headaches. Heinz's little bodies, increase of content of sulfhemoglobin (from 0,5 to 4%) come to light.
Verification of the diagnosis Constant cyanosis is more characteristic of hereditary forms, at the acquired forms it has short-term character. At the acquired form of methemoglobinemias and sulfhemoglobinemias unlike hereditary methemoglobinemias are found Heinz's little bodies.
Methemoglobinemias it is necessary to differentiate also with some heart diseases and a respiratory organs which are proceeding with cyanosis, having characteristic clinical features inherent to them.
The test confirming existence of HbM is research of ranges of acid forms of a hemolysate with preliminary transfer of Hb which is contained in them in a met-form. The electrophoresis on agar gel at rn 7,1 allows to find HbM (a brown strip) and to distinguish it from NBA (a scarlet strip). The greatest diagnostic value gets a method of isoelectrofocusing by means of which the best division of M and And haemo globins is reached at addition to a ferricyanide hemolysate.
Treatment Many cases of the hereditary and acquired methemoglobinemias of treatment do not demand, there is enough termination of reception of the medicine which exerted an adverse effect. At a severe disease appoint a bed rest, oxygen, ascorbic acid inside or parenterally in a daily dose of 500 — 1000 mg, 1% solution of a methylene blue at the rate of 1 — 2 mg/days are entered into 40% to glucose, cardiotonic means, Cytitonum or lobelias. At a severe form of a sulfhemoglobinemia exchange hemotransfusion is recommended.
The forecast of methemoglobinemias favorable though at sharp increase of maintenance of a methemoglobin in erythrocytes lethal outcomes are possible.
Patients with methemoglobinemias need the sparing mode, have to avoid contact with substances of the oxidizing action, exclude the situations leading to a hypoxia.