KIDNEY DIAGNOSIS DIABETES. Etiology and pathogenesis. An inherited disease in which the kidneys are not able to produce urine with a higher osmolar concentration than the osmolarity of glomerular ultrafiltrate plasma, which is associated with a loss of sensitivity of the renal tubules to antidiuretic hormone (ADH). Nephrogenic diabetes insipidus should be distinguished from neurohypophysial diabetes, in which the kidney reactions to ADH are preserved, but the processes of hypothalamic neurosecretion are impaired.
With nephrogenic diabetes insipidus, the homeostatic function of the kidneys, aimed at maintaining water-salt balance, is significantly impaired. This leads to significant fluctuations in the osmotic pressure of blood plasma and hyperelectrolytemia: the concentration of sodium in plasma can increase up to 180 meq / l, chlorine up to 160 meq / l. These fluctuations are especially great in young children, in whom the feeling of thirst is not developed. Losses of significant amounts of water lead to the development of dehydration, toxicosis.
The clinical picture. The disease manifests itself at 3-6 months of age with abundant diuresis, vomiting, a tendency to constipation, and a febrile state. Thirst may be absent. The volume of daily urine of an infant can reach 2 liters, at an older age – 5 Yul.
“Salt fever” is observed, convulsive conditions are possible. Persistent violations of the water-salt balance can lead to the development of malnutrition, delayed physical, and in some children, mental development. With sufficient introduction of fluid this is not observed.
In older children, the state of dehydration rarely develops, fluid loss is compensated by its intake, and the total plasma osmolality is maintained within normal limits. Indicators of glomerular renal filtration, excretion of phosphates, amino acids, glucose, as a rule, also do not go beyond the norm. Cases of a peculiar form of the disease are known: sensitivity to AD G is absent only at night, but is restored during the day. A renal biopsy is necessary for diagnosis. Microdissection reveals a significant (half) shortening of the proximal tubule of the nephron. In a histological examination, it is necessary to distinguish this condition from nephronophysis, chronic hypokalemia, idiopathic hypercalciuria, cystinosis.
Diagnosis and differential diagnosis. Functional studies can clarify the diagnosis of the disease. A urine concentration test is based on the exclusion of water intake for 12 hours (for children, it is better to use a night break, for example, from 19 o’clock in the evening to 7 o’clock in the morning). Carrying out this test is permissible only in doubtful cases, since with obvious diabetes insipidus it is unsafe. In healthy children, the osmolar concentration of urine rises to 1000 mosm / l, the osmotic concentration coefficient exceeds 2.5. In diabetes insipidus, the osmolarity of urine approximately corresponds to the plasma osmolarity, the osmotic coefficient is about 1; administration of ADH is accompanied by a decrease in urine output and an increase in osmolarity of urine. With nephrogenic diabetes, reactions to the administration of ADH are completely absent.
ADH is administered intramuscularly in a single dose of 3 to 8 units, depending on age. Too high doses can lead to a distortion of the results of the study due to spasm of the vessels of the kidneys. Pituitrin for injection containing 1 ml of 5 units can be used for sampling. Children under 1 year old are injected with 0.1-0.15 ml, 2-5 years old, 0.2-0.4 ml, 6-12 years old, 0.4-0.6 ml. After the IM injection of pituitrin, several one-hour portions of urine are collected (3-5 hours) and its relative density is measured. Normally and with neurohypophysial diabetes, the amount of urine excreted significantly decreases, and its relative density increases significantly, with renal diabetes insipidus there is no reaction. Differential diagnosis of diabetes insipidus is not particularly difficult. In addition to neurohypophysial diabetes insipidus, it is necessary to keep in mind the polyuria that develops in patients with diabetes mellitus as a result of osmotic diuresis.
Treatment of renal diabetes insipidus is symptomatic and is mainly aimed at maintaining water-salt balance by introducing sufficient amounts of fluid. If the child refuses to take the liquid, as well as with the development of signs of dehydration, the liquid is administered intravenously, with a 5% glucose solution being used more often.
The sulfonamide diuretics have a paradoxical effect on renal water transport in this disease: the administration of hypothiazide at a dose of 25-100 mg per day is accompanied by a significant decrease in diuresis. The antidiuretic effect of these drugs persists for some time and after their cancellation, subject to a significant restriction of salt in the diet. In the treatment with hypothiazide, constant monitoring of the acid-base balance of the blood, as well as the potassium content in the plasma, should be ensured.
Due to the possibility of developing hypertensive dehydration, febrile illnesses, relocation to areas with a hot climate, and surgical interventions pose a serious danger to patients, especially young children.
The outlook is relatively favorable.
Prevention – genetic counseling.