Syndrome of inappropriate antidiuretic hormone overview
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Vindhya BellamKonda, M.B.B.S [2]
Overview
The syndrome of inappropriate antidiuretic hormone (SIADH) is a condition commonly found in the hospital population, especially in patients being hospitalized for central nervous system (CNS) injury. This is a syndrome characterized by excessive release of antidiuretic hormone (ADH or vasopressin) from the posterior pituitary gland or another source. The result is hyponatremia, and sometimes fluid overload.
Syndrome of inappropriate antidiuretic hormone production (SIADH) is a condition in which the body develops an excess of water and a decrease in sodium concentration. It may be caused by central nervous system diseases, cancers, pulmonary diseases and some drugs. Signs and aymptoms vary widely. Some patients with SIADH may become severely ill, or may have no symptoms at all. Usual symptoms include nausea, vomiting, loss of appetite, fatigue, weakness,even consciousness disorders. Blood tests of hyponatremia (sodium <135 mEq/L) and low serum osmolality (<280 mOsm/kg) may prompt the diagnosis of SIADH. Treatment depends on the causes. Sharp restriction of water intake and addition of a high concentration of sodium may get immediate improvement. Prognosis of SIADH varies widely, depending on the causes.
Historical Perspective
Syndrome of SIADH was initially described by Leaf and Mambi in the year 1951.Later it was described by researchers from Boston, Massachusetts and Bethesda, Maryland (including Dr Frederic Bartter) in two patients with lung cancer in the year 1957.The condition is occasionally referred to as Schwartz-Bartter syndrome.
Classification
Four different types of SIADH, were classified- defined by the pattern of AVP secretion across a range of plasma osmolalities.
Pathophysiology
Clinical picture of SIADH may result from genetic disorders that result in antidiuresis. A mutation affecting the gene for the renal V2 receptor, which some investigators have named nephrogenic syndrome of inappropriate antidiuresis, has been found to cause clinically significant hyponatremia. Congenital nephrogenic diabetes insipidus is characterized by a resistance of the renal collecting duct to the action of the arginine vasopressin hormone responsible for the inability of the kidney to concentrate urine. The X-linked form is due to inactivating mutations of the vasopressin 2 receptor gene leading to a loss of function of the mutated receptors. Conversely, the nephrogenic syndrome of inappropriate antidiuresis (NSIAD) is linked to a constitutive activation of the V(2)-receptor due to activating mutations with clinical and biological features of inappropriate antidiuresis but with low or undetectable plasma arginine vasopressin hormone levels.[1]
Causes
SIADH is caused by excess of renal water reabsorption through inappropriate antidiuretic hormone secretion, there are various causes attributed to SIADH ranging from malignancies, drugs, central nervous system causes, infectious and other miscellaneous causes. Some of the most common causes are : malignancies like small cell lung cancer, drugs like selective serotonin reuptake inhibitors, and carbamazapine.[2]
Differentiating Syndrome of inappropriate antidiuretic hormone overview from Other Diseases
SIADH consists of hyponatremia, inappropriately elevated urine osmolality, excessive urine sodium and decreased serum osmolality in a euvolemic patient without edema. These findings should occur in the absence of diuretic treatment with normal cardiac, renal, adrenal, hepatic and thyroid function. Hyponatremia occurs in about 30% of hospitalized patients and SIADH is the most frequent cause of hyponatremia. Differentiating hyponatremia due to SIADH from other causes of hyponatremia becomes essential to evaluate the treatment plan. [1]. Syndrome of inappropriate antidiuretic hormone must be differentiated from Cerebral salt wasting , Adrenal insufficiency, Hypopituitarism, Hypothyroidism,Psychogenic polydipsia
Epidemiology and Demographics
SIADH can occur at any age. It's incidence depends on various possible etiologies. Hyponatremia is the most common electrolyte abnormality in hospitalized patients. Prevalence of hyponatremia in hospitalized patients from multiple studies came to be about 2.5%-30%.SIADH was the most common clinical setting in hospitalized patients with hyponatremia. The incidence and prevalence of SIADH in particular is less thoroughly studied in the literature.
Risk Factors
The most common causes of SIADH are malignancy, pulmonary disorders, CNS disorders and medications.
Screening
There are no screening guidelines for SIADH
Natural History, Complications, and Prognosis
Natural History
Patients with SIADH have different characteristics and a different prognosis according to SIADH etiology. Serum sodium concentration at short-term follow-up is predictive of long-term survival. These findings might have diagnostic and treatment-related implications.Some of the complications of SIADH are: Hyponatremia,cerebral edema, centralpontine myelinolysis(occurs when sodium levels are corrected too rapidly).
Complications
Some of the complications of SIADH are: Hyponatremia Central pontine myelinolysis ( When sodium levels are corrected too rapidly) Cerebral edema
Prognosis
The prognosis of Syndrome of inappropriate antidiuretic hormone (SIADH) depends largely on its cause. If the cause is drugs, SIADH usually improves after stopping a drug. If SIADH is associated with some infection, treating the infection may be important. For those SIADH with cancers, the outcomes may be poor. Patients with SIADH have different characteristics and a different prognosis according to SIADH etiology. Serum sodium concentration at short-term follow-up is predictive of long-term survival. These findings might have diagnostic and treatment-related implications. [3]
Diagnosis
Diagnostic Criteria
History and Symptoms
The main problem in patients with SIADH is excess of water retention and low sodium levels. Symptoms depend on the levels of sodium in the blood and the rate at which the level of sodium falls. Symptoms may be non-specific like generalised fatigue, weakness,but if severe symptoms such as irritability,nausea, vomiting,muscle weakness and cramps,loss of appetite, confusion,personality changes,hallucinations,seizures,stupor and coma.
Physical Examination
Laboratory Findings
Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Surgery
Prevention
References
- ↑ 1.0 1.1 Pillai BP, Unnikrishnan AG, Pavithran PV (2011). "Syndrome of inappropriate antidiuretic hormone secretion: Revisiting a classical endocrine disorder". Indian J Endocrinol Metab. 15 Suppl 3: S208–15. doi:10.4103/2230-8210.84870. PMC 3183532. PMID 22029026.
- ↑ Oh JY, Shin JI (2014). "Syndrome of inappropriate antidiuretic hormone secretion and cerebral/renal salt wasting syndrome: similarities and differences". Front Pediatr. 2: 146. doi:10.3389/fped.2014.00146. PMC 4302789. PMID 25657991.
- ↑ Shepshelovich D, Leibovitch C, Klein A, Zoldan S, Milo G, Shochat T, Rozen-zvi B, Gafter-Gvili A, Lahav M (2015). "The syndrome of inappropriate antidiuretic hormone secretion: Distribution and characterization according to etiologies". Eur. J. Intern. Med. 26 (10): 819–24. doi:10.1016/j.ejim.2015.10.020. PMID 26563934.