Syndrome of inappropriate antidiuretic hormone secretion

When Schwartz - Bartter syndrome or syndrome of inappropriate antidiuretic hormone secretion ( SIADH ) is one in relation to the blood plasma osmolality, inappropriately high secretion of antidiuretic hormone ( ADH, Syn: Adiuretin, vasopressin ). This leads to inadequate fluid excretion by the kidney with formation of an insufficiently diluted urine. The disease is biochemically characterized by a hypotonic hyperhydration with dilutional (serum sodium < 135 mmol / l) and an inappropriately high urine osmolality (> 1000 mOsm / kg). The most common cause is a small cell lung cancer in terms of a paraneoplastic effect.

The Schwartz - Bartter syndrome is indistinguishable from Bartter 's syndrome, a disease of the kidney tubules.

Causes

The Schwartz - Bartter syndrome occurs, for example, after craniocerebral trauma, meningitis or encephalitis, in aneurysms after major burns, in hypothyroidism or intracranial tumors, pneumonia or tuberculosis. As a paraneoplastic syndrome may (particularly when undifferentiated small cell carcinoma) arise for example during lung carcinomas. It was also porphyria and as a side effect of antidepressants from the group of tricyclic antidepressants (eg, amitriptyline, nortriptyline ), or serotonin reuptake inhibitors ( zBEscitalopram ), neuroleptics (such as amisulpride, chlorpromazine, fluphenazine, flupentixol, haloperidol, trifluoperazine, thioridazine, thiothixene and risperidone ), cytostatics and observed under the antiarrhythmic agent amiodarone. It is further believed that there may be after surgery a temporary inappropriate secretion of antidiuretic hormone in almost all patients.

Symptoms

It consists of the symptom complex of mainly secreted by the kidney, or impacted electrolytes together. In the course of this disease arises a dilution effect due to inappropriate antidiuretic hormone secretion and thus reduced water excretion, a. One speaks in this case of a hypotonic Hyperhydratations syndrome. When blood tests show hyponatremia, hypophosphatemia, as well as hypokalemia with metabolic alkalosis hypochloraemic.

Symptoms of relative hyponatremia depend on how quickly the sodium is diluted. There are headaches, personality changes in terms of increased irritability or lethargy, nausea, vomiting, confusion to delirium and impaired consciousness up to coma possible. An increase in the sodium concentration should be carried out slowly, to prevent the development of a central pontine myelinolysis. In addition to muscle weakness and cramps may occur myoclonus and seizures. The reflexes are sometimes reduced or increased. Edema do not occur because of the limited to around three to four liters of water retention.

Diagnosis

The following examinations and laboratory parameters provide information about the diagnosis:

  • Decreased serum osmolality (< 270 mosmol / kg)
  • Dilutionshyponatriämie ( [Na ] < 135 mmol / l in the serum)
  • Elevated central venous pressure
  • No edema or ascites
  • Low urine volume per time
  • Inappropriately high urine osmolality / urine specific gravity
  • Inappropriately high sodium concentration in the urine ( > 20 mmol / liter)

The determination of the ADH concentration in the blood is of little use. In practice, in fact shows that the values ​​may be normal or elevated, but by no means have to be increased.

Therapy

Crucial to the treatment decision is the clinical symptoms and the identification and treatment of trigger a SIADH. In asymptomatic cases, a sufficient fluid intake restriction as a rule. Especially in the presence of neurological symptoms need action: slow infusion of isotonic ( 0.9%) or hypertonic (10%) saline for substitution. If excessive infusion of saline pontine myelinolysis threatening disturbances of consciousness, or seizures. As a new and specific treatment option Vaptane now been approved for the treatment of SIADH in Europe. Since August 2009 Tolvaptan is the first oral ADH antagonist also in Germany. Vaptane block the action of ADH on the kidney and thus promote the excretion of electrolyte -free water.

In addition, it is important to note that accompany hyponatremia often also present hypokalemia. Substitution of potassium for sodium is at the same time released from the cell. Thus, a potassium substitution also contributes to the balance of hyponatremia.

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