Syndrome of inappropriate antidiuretic hormone differential diagnosis

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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

SIADH consists ofhyponatremia, inappropriately elevatedurine 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. Syndrome of inappropriate antidiuretic hormone must be differentiated from cerebral salt wasting , adrenal insufficiency, hypopituitarism, hypothyroidism,psychogenic polydipsia

Differentiating Syndrome of inappropriate antidiuretic hormone from other Diseases

SIADH must be differentiated from cerebral salt wasting, adrenal insufficiency, hypopituitarism, hypothyroidism, and psychogenic polydipsia

Disease	Causes	Symptoms	Diagnosis and treatment
SIADH	SIADH 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.	Nausea / vomiting Cramps Depressed mood Irritability Confusion Hallucinations Seizures ,stupor or coma	Hyponatremia <135 mmol/l Decreased effective serum osmolality<275mosm Urine sodium concentration>40mmol/litre Plasma uric acid <200;FeUrate>12% Absence of edematous disease likecardiac failure, liver cirrhosis,nephrotic syndrome. Normal adrenal and thyroid function
Cerebral salt wasting syndrome	Cerebral salt wasting syndrome is defined as therenal loss of sodium during intracranial disease leading to hyponatremia and a decrease in extracellular fluid volume. Trauma Tumor Hematoma	The patient is Hypovolemic Hyponatremic	Treatment is with adequate Hydration and Sodium replacement
Adrenal insufficiency	Adrenal insufficiency ranges from mild nonspecific symptoms to life-threatening shock like condition. An important distinction in these patients is the presence ofmineralocorticoid deficiency. Those with secondary or tertiary adrenal insufficiency will typically have preservedmineralocorticoid function due to the separate feedback systems. Adrenal insufficiency can be Primary Secondary Tertiary Common causes of primary adrenal insufficiency: Autoimmune Iatrogenic Drugs Adrenal hemorrhage Cancer Infection Congenital Secondary adrenal insufficiency refers to decreased adrenocorticotropic hormone (ACTH) stimulation of the adrenal cortex and therefore does not affect aldosterone levels. Most common causes are: Traumatic brain injury (TBI) Panhypopituitarism Tertiary adrenal insufficiency refers to decreased hypothalamic stimulation of the pituitary to secrete ACTH Exogenoussteroid administration is the most common cause of tertiary adrenal insufficiency	Fatigue Muscle weakness Loss of appetite Weight loss Abdominal pain Diarrhea Vomiting Chronic disease is characterized by Weight loss Sparse axillary hair Hyperpigmentation Orthostatic hypotension. Acute addisonian crisis is characterized by: Fever Hypotension	The diagnosis of Addisons disease is made through rapid ACTH administration and measurement of cortisol. Lab findings include: White blood cell count with moderate neutropenia lymphocytosis eosinophilia Elevated serumpotassium and urea nitrogen Low sodium Low bloodglucose Morning low plasma cortisol. The definitive diagnosis is the cosyntropin or ACTH stimulation test. Acortisol level is obtained before and after administering ACTH. A normal person should show a brisk rise in cortisol level after ACTH administration. Management: The management of Addison disease involves: Gluocorticoid Mineralocorticoid Sodium chloride replacement. Adrenal crisis: In adrenal crisis,measure cortisol level,then rapidly administer Fluids Hydrocortisone
Hypopituitarism	Hypopituitarism is defined as the partial or complete loss of anterior pituitary function that can result from acquired or congenital causes. Etiology is as follows: Pituitary tumors Sellar tumors Head trauma Infection Empty sella Infiltration Idiopathic Congenital	Signs and symptoms ofhypopituitarism vary, depending on the deficient hormone and severity of the disorder,some of the symptoms may be as follows: Fatigue Weight loss Decreased libido Decreased appetite Facial puffiness Anemia Infertility Cold insensitivity. Amenorrha Inability to lactate in breast feeding women Decreased facial orbody hair in men Short stature in children	The diagnosis is based on detailed investigation of symptoms of target endocrine gland function relative to the corresponding pituitaryhormone deficiency The clinical manifestations ofhypopituitarism result from the degree of the specific hormone deficiency A thorough and longitudinal history andphysical examination, including visual field testing, are important. Hypopituitarism may involve from one to all endocrine axes regulated by the pituitary In order of frequency: growth hormone deficiency>secondary hypogonadism>secondary hypothyroidism>secondary adrenal failure). The treatment of permanent hypopituitarism consists of replacement of the peripheral hormones Hydrocortisone DHEA Thyroxine Testosterone or oestradiol Growth hormone Surgery and/or Radiotherapy to restore normal endocrine function and quality of life Patients with hypopituitarism require lifelong monitoring of serum hormone levels and symptoms of hormone deficiency or excess Long-term care and monitoring of patients with hypopituitarism requires a experienced endocrinologist
Hypothyroidism	Hypofunctioning of the thyroid gland due to multifactorial etiology ranging from congenital to autoimmune causes described below: Congenital Autoimmune Drugs Post surgery Post radiation Infiltrative e.g., amyloid	Fatigue Constipation Dry skin Weight gain Cold intolerance Puffy face Hoarseness Muscle weakness Elevated blood cholesterol level Bradycardia Myopathy Depression Impaired memory	Diagnosis of hypothyroidism is based on blood tests: T3(triiodothyronine) T4(Thyroxine) and TSH (thyroid stimulating hormone). Signs and symptoms are neither sensitive nor specific for the diagnosis. TSH is the most sensitive tool for screening,diagnosis and treatment follow up, whenpituitary is normal. The drug of choice for treatment is Levothyroxine
Psychogenic polydipsia	Also called asprimary polydipsia is characterized bypolyuria and polydipsia. Causes are: Defect in the hypothalamus Adverse effect of a medication Traumaticbrain injury Psychiatric disorders such as schizophrenia	Polyuria Polydipsia Confusion Lethargy Psychosis Seizures and Sometimes, even death	Evaluation ofpsychiatric patients with polydipsia warrants a comprehensive evaluation for other medical causes of polydipsia, polyuria,hyponatremia, and the syndrome of inappropriate secretion of antidiuretic hormone. The management strategy inpsychiatric patients should include: Fluid restriction andbehavioral and pharmacologic modalities. The water deprivation test is the gold standard test

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