Syndrome of inappropriate antidiuretic hormone secretion (SIADH) can be primary or secondary to various etiologies ranging from drugs to tumors. It is characterized primarily by hyponatremia and low serum osmolality. The syndrome is caused by the inappropriate synthesis of the antidiuretic hormone (ADH) in patients with normal plasma volume levels [1]. Risk factors for SIADH include advanced age as aging is associated with elevated levels of ADH and atrial natriuretic peptide (ANP), and increased susceptibility to osmotic stimulation [2] [3]. In addition, the elderly may be on several medications which can cause SIADH. Postoperative patients, patients with head injury or those on mechanical ventilation, as well as individuals with tumors secreting ADH, are other groups who are at high risk of developing SIADH. Factors like stress, low blood pressure, severe pain, and general anesthesia can also predispose to SIADH.

Clinical presentation of SIADH depends on the severity and rate of hyponatremia development. Slowly progressive hyponatremia is usually asymptomatic while manifestations in acute, rapidly progressing hyponatremia include confusion, tremors, ataxia, myoclonus, asterixis, abnormal reflexes, dysarthria, seizures, coma. Neurological features appear as intracranial pressure increases and cerebral edema develops. Chronic moderate hyponatremia is associated with a poor reaction time, cognitive dysfunction, and ataxia with frequent falls [4] [5].

• Falling

  When sodium level falls slowly over days or weeks (chronic hyponatremia), the brain cells have time to adjust and the acute symptoms such as brain swelling don't occur. [medlineplus.gov]

• Severe Pain

  Factors like stress, low blood pressure, severe pain, and general anesthesia can also predispose to SIADH. Clinical presentation of SIADH depends on the severity and rate of hyponatremia development. [symptoma.com]

  pain, nausea, and stress. [medcaretips.com]

• Anemia

  On day 26 of linezolid therapy, the drug was discontinued due to development of progressive anemia (hemoglobin concentration, 6.7 g/dL). [ncbi.nlm.nih.gov]

  Several major points supported this conclusion including: (1) past history of MALT; (2) occurrence of itching (characteristic symptom of lymphoma); (3) CT scan findings suggested lymphoma; and (4) the manifestation of progressive anemia. [bmcendocrdisord.biomedcentral.com]

• Antipsychotic Agent

  Aripiprazole is a newer atypical antipsychotic agent used for effective treatment of schizophrenia. [ncbi.nlm.nih.gov]

• Dyspnea

  History may also provide information about a head injury, drug abuse, long-standing pain, neurological symptoms, and features of lung tumors or pathology such as dyspnea, chronic cough, and hemoptysis. [symptoma.com]

• Nausea

  A 70-year-old female patient had nausea and collapsed. Although euvolemic, pathological laboratory findings showed hyponatremia and hypoosmolality, and cerebral magnetic resonance imaging showed hypertrophic pachymeningitis. [ncbi.nlm.nih.gov]

• Vomiting

  Four days later she developed vomiting with serum sodium 119 mEq/L. Fluid restriction, which the woman had not performed, was reinstituted and she was discharged on day 17. [ncbi.nlm.nih.gov]

  Early symptoms may be mild and include cramping, nausea, and vomiting. In severe cases, SIADH can cause confusion, seizures, and coma. Treatment usually begins with limiting fluid intake to prevent further buildup. [healthline.com]

• Loss of Appetite

  Severe cases may involve these symptoms: irritability and restlessness loss of appetite cramps nausea and vomiting muscle weakness confusion hallucinations personality changes seizures stupor coma Your doctor will ask for your complete medical history [healthline.com]

  The onset of symptoms may be acute or chronic, with sudden or gradual loss of appetite, nausea and vomiting, sleepiness, confusion and disorientation, and ultimately seizures, coma, and death. [britannica.com]

• Suggestibility

  The authors suggest that SIADH is an uncommon presenting feature of SACs and that syndrome resolution is possible with cyst decompression. [ncbi.nlm.nih.gov]

• Seizure

  After the dosage was titrated to 6 mg/d, she experienced generalized seizure attacks. [ncbi.nlm.nih.gov]

• Confusion

  Afterwards, she drank 6 litres of water and gradually developed nausea and vomiting, confusion, lethargy, muscle weakness, spasms and cramps, seizure, decreased consciousness level and short-term memory loss. [ncbi.nlm.nih.gov]

  In severe cases, SIADH can cause confusion, seizures, and coma. Treatment usually begins with limiting fluid intake to prevent further buildup. Additional treatment will depend on the cause. Another name for the syndrome is “ectopic ADH secretion.” [healthline.com]

• Headache

  CASE SUMMARY: A 76-year-old white woman who was being treated with lisinopril and metoprolol for hypertension presented with headaches accompanied by nausea and a tingling sensation in her arms. [ncbi.nlm.nih.gov]

  Symptoms and signs include headache, confusion, disorientation, hostility and other mental aberrations without motor or sensory defects. Reflexes are normal and there is no dehydration or oedema, and no signs of renal, hepatic, or cardiac disease. [whonamedit.com]

• Stupor

  Symptoms, in more severe cases of SIADH, may include: Nausea or vomiting Cramps or tremors Depressed mood,memory impairment Irritability Personality changes, such as combativeness, confusion, and hallucinations Seizures Stupor or coma The symptoms of [chop.edu]

  Severe cases may involve these symptoms: irritability and restlessness loss of appetite cramps nausea and vomiting muscle weakness confusion hallucinations personality changes seizures stupor coma Your doctor will ask for your complete medical history [healthline.com]

  As the serum sodium falls to < 115 mEq/L (< 115 mmol/L), stupor, neuromuscular hyperexcitability, hyperreflexia, seizures, coma, and death can result. [merckmanuals.com]

  […] if serum Na + is not corrected after 24-48 hr of fluid restriction or if the patient has a low urinary electrolyte free water excretion Emergency Care Aggressive management of hyponatremia is indicated in patients with severe symptoms like seizures, stupor [medcaretips.com]

• Lethargy

  A 66-year-old woman, diagnosed with Parkinson disease, developed asthenia, anorexia, weight loss, lethargy and feeling of muscle weakness, and severe hyponatremia, with diagnostic criteria for SIADH, after exposure to amantadine. [ncbi.nlm.nih.gov]

  Symptoms of SIADH include: fatigue anorexia headache nausea vomiting muscle cramps worsening mental status, including lethargy, weakness, irritability, agitation, confusion, combativeness, delirium, disorientation, hallucinations and poor balance seizures [cancer.ca]

  Symptoms can be subtle and consist mainly of changes in mental status, including altered personality, lethargy, and confusion. [merckmanuals.com]

The diagnosis of SIADH is based on laboratory findings but patient history can raise suspicion of the condition and its underlying etiology. The onset of the manifestations is an indicator of whether the condition is acute or chronic. History may also provide information about a head injury, drug abuse, long-standing pain, neurological symptoms, and features of lung tumors or pathology such as dyspnea, chronic cough, and hemoptysis. It is essential to elicit whether the patient has consumed excessive fluids (an indicator of psychogenic polydipsia) or has received hypotonic fluids.

Laboratory tests include serum electrolytes, bicarbonate, creatinine, blood urea nitrogen, uric acid, cortisol, and thyroid stimulating hormone (TSH). Once the tests reveal hyponatremia, the urine and plasma osmolality is determined along with urine sodium. SIADH is confirmed using Bartter and Schwartz criteria [6]:

• Hyponatremia with reduced plasma osmolality with values <275 mOsm/kg

• Relatively increased urine osmolality (>100 mOsm/kg)

• Normal plasma volume

• Elevated levels of urine sodium (>20 mEq/L)

• Exclusion of hypothyroidism, hypoadrenalism, cardiac failure, pituitary dysfunction, renal dysfunction, liver disease, and diuretic use.

• No clinical features of dehydration e.g. mucosal dryness, loss of skin turgor, or hypotension

Imaging studies like chest X-ray may show a lung tumor as the underlying cause of SIADH while computed tomography (CT) of the head and magnetic resonance imaging (MRI) of the brain may reveal features of cerebral edema or may detect an underlying brain tumor.

Patients who are already hospitalized may develop SIADH. Diagnosis of the condition in such patients may be challenging especially if they are on diuretics [7]. Fractional excretion of uric acid (FE-UA) is very useful in these patients to diagnose SIADH [8].

• Hypouricemia

  Hypouricemia is the rule in SIADH, whereas hyperuricemia commonly accompanies volume contraction. This report presents an AIDS patient with SIADH and normouricemia secondary to pyrazinamide and ethambutol. [ncbi.nlm.nih.gov]

  Nephron 64 : 189 – 192, 1993 ↵ Beck LH: Hypouricemia in the syndrome of inappropriate secretion of antidiuretic hormone. [cjasn.asnjournals.org]

  Hypouricemia and an elevated FEUA may be seen in either salt-wasting syndromes or SIADH. In SIADH, both typically resolve after correction of hyponatremia but persist in those with salt-wasting syndromes. [medcaretips.com]

  Hypouricemia appears to occur in any volume expanded state and, therefore, lacks both sensitivity and specificity for making the diagnosis of SIADH. [razianesth.freeservers.com]

• Urea Decreased

  Nephron, 1993, vol. 63 (pg. 468 - 470 ) 35 Rapid correction of hyponatraemia with urea may protect against brain damage in rats, Clin Sci (Lond), 1989, vol. 77 (pg. 351 - 355 ) 36 Treatment of hyponatraemia by urea decreases risks of brain complications [doi.org]

The most influential variables in our analysis were reduction in hospital length of stay, duration of treatment and long term treatment with tolvaptan in SCLC patients. [ncbi.nlm.nih.gov]

Melanoma is a relatively common cancer and is often associated with a dire prognosis once diagnosed as metastatic. [ncbi.nlm.nih.gov]

[…] according to SIADH etiology. [ncbi.nlm.nih.gov]

Syndrome of inappropriate antidiuretic hormone secretion (SIADH) can be primary or secondary to various etiologies ranging from drugs to tumors. It is characterized primarily by hyponatremia and low serum osmolality. [symptoma.com]

Epidemiology, symptoms, and treatment characteristics of hyponatremic psychiatric inpatients. J Clin Psychopharmacol. 2013; 33(6): 799–805. 6. Padhi R, Panda BN, Jagati S, Patra SC. Hyponatremia in critically ill patients. [jpccr.eu]

In this article, we review the epidemiology and presentation of patients with hyponatremia, the pathophysiologic groups for the disorder with respect to sodium and water balance and the diagnostic measures for determining the correct pathophysiologic [doi.org]

Hyponatremia: a prospective analysis of its epidemiology and the pathogenetic role of vasopressin. Ann Intern Med. 1985;102:164–8. PubMed CrossRef Google Scholar 3. [link.springer.com]

Idiopathic Epidemiology Occurrence in the United States Hyponatremia is the most common electrolyte derangement occurring in hospitalized patients. [emedicine.com]

In this article, we review the epidemiology and presentation of patients with hyponatremia, the pathophysiologic groups for the disorder with respect to sodium and water balance and the diagnostic measures for determining the correct pathophysiologic [doi.org]

The article presents pathophysiology, diagnostics and recommendations of management of this oncological emergency. [ncbi.nlm.nih.gov]

With such widespread use of cisplatin in a diverse range of cancers, prompt recognition is crucial to detect and prevent severe neurological sequelae. [ncbi.nlm.nih.gov]

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