SIADH

SIADH – General Information

SIADH or syndrome of inappropriate antidiuretic hormone secretion is a medical condition that is characterized by the presence of hyponatremia, which consists of an unusual urine osmolality, excessive urine sodium elimination and a decreased serum osmolality. These manifestations can also be accompanied by several other symptoms and can develop in the setting of normal and balanced cardiac, adrenal, renal, hepatic and thyroid functions. The disease can also be caused by an inappropriate secretion of ADH, which is the antidiuretic hormone or vasopressin that interferes with the patient’s renal excretion of water leading to an excessive elimination of concentrated urine and hyponatremia. In most cases, the patient’s serum sodium concentration is controlled by the balance of water intake, renal excretion of sodium and water conservation managed by the distal renal tubule.

All these processes are controlled by the secretion of ADH, and a disorder of any of these processes can lead to an inappropriate antidiuretic hormone secretion, causing SIADH. Generally, the antidiuretic hormone (ADH) is produced by the posterior pituitary gland, which also controls the kidney functions. If the secretion of ADH is affected, it also produces a disorder that damages the patient’s excretion system, leading to a production of concentrated urine, inability to excrete water and consequently hyponatremia. There are also cases in which SIADH is not caused by a disorder on the posterior pituitary gland, but by the presence of ADH secreting tumors or other central nervous system disorders, pulmonary diseases and even drugs. This makes the disease challenging to treat with minimal benefits. 

SIADH – Symptoms

The most common signs and symptoms of SIADH usually appear due to a dysfunction of the central nervous system and are increased in severity due to the presence of hyponatremia. When a patient suffers from SIADH, he is likely to experience the following signs and symptoms: anorexia, malaise and nausea, as first manifestations, followed by irritability, confusion, weakness, headache, muscle cramps, seizures and coma, as manifestations of the advanced stage of the disease. These symptoms can also be developed due to the shifting of the osmotic fluid that causes cerebral edema and increased intracranial pressure. There are also cases in which the patient can experience few to no signs and symptoms at all.

If the patient presents a severe decrease in the sodium concentration, he is susceptible to developing life threatening complications. It is very important for the doctor to know any historical details about the patient’s general health status and any other factors that may have caused hyponatremia such as diet, fluid intake, gastrointestinal losses, the amount of urine excreted, and the use of certain medications. There are also cases in which the information can help the doctor in identifying the condition that caused the disease as a complication or side effect of a medicine. The most common causes that can lead to SIADH include central nervous system disorders such as subarachnoid bleeding, delirium tremens and multiple sclerosis; pulmonary disorders such as pneumonia, lung abscess, cystic fibrosis and tuberculosis; lungs or pancreas carcinoma. Drugs such as Vincristine, Thioridazine and Clofibrate as well as certain surgical procedures may also cause this affection.

SIADH – Treatment

Hormonal deficiencies are serious medical conditions that require close and intense medical help because if they remain undiagnosed and untreated they can affect other endocrine glands, causing further imbalance in the human body. One of the most important endocrine disorders is SIADH or syndrome of inappropriate antidiuretic hormone (ADH). This hormone is produced by the posterior lobe of the hypophysis and has a major role in retaining the water in the body. When this type of hormonal imbalance occurs and as soon as you experience one or more of the signs and symptoms that we have listed above, you are advised to immediately consult your health care provider. You may also be advised to contact an internist or a nephrologist if you suffer from severe symptoms of hyponatremia. During the medical examination you will be asked about what signs and symptoms you experience and about your personal and family medical history. Because the manifestations of this medical condition may be similar to those caused by other affections, the health care provider may perform several additional tests that will help him rule out some possibilities.

Urine and blood analysis are the most common tests that reveal increased levels of natrium and sodium, low amounts of uric acid, albumin, creatinine and BUN (blood urea nitrogen), suppression of rennin-angiotensin system, maintained hypervolemia and various concentrations of atrial natriuretic peptide. These tests serve to detect if the patient has SIADH. These results will also indicate what treatment option is best for each patient. The management of this disorder focuses on treating the underlying causes if present and correcting the imbalance.

In order to obtain an increase of serum sodium, doctors will recommend fluid restriction. If SIADH has evolved to a more severe stage and the symptoms are complex (convulsions, confusion and coma), the health care providers will recommend IV (intravenous) saline. Treatment options based on drugs are also used in managing SIADH. Some of the most commonly used drugs include Conivaptan, Demeclocycline and Tolvaptan. Conivaptan is an antagonist for V1A and V2 vasopressin receptors and is administered for hospitalized patients in the setting of hypothyroidism or who are diagnosed with pulmonary disorders, adrenal insufficiency and SIADH. Demeclocycline is used in chronic cases when the restrictions of fluid are very difficult to maintain. This drug is the most potent AP inhibitor. Tolvaptan is an antagonist of V2 vasopressin receptors taken orally. Correcting hyponatremia can be a difficult thing to do because a rapid rise of the sodium levels may cause another medical condition, called central pontine myelinolysis. All the drugs must be taken as the doctors recommended so that you avoid developing further more severe complications that interfere with the process of healing and delay the recovery. You must avoid losing a dose or overdosing. Also, if you do not notice any improvements of your health status call your health care provider and ask him to change the prescription. Before taking any medication, be sure you are not allergic to any of its major ingredients.