26 Questions
What is the primary manifestation of hyponatremia when sodium levels decline rapidly or reach a level less than 125 mEq/L?
Lethargy, confusion, agitation, headache, nausea, and vomiting
What is a characteristic of urine osmolality in patients with hyponatremia?
Higher than serum osmolality
What is the purpose of administering a water load and then hypertonic saline in diagnosing diabetes insipidus?
To stimulate ADH secretion and decrease urine flow
What is the range of plasma osmolality in patients with diabetes insipidus?
280 - 310 mOsm/kg
What is the primary cause of polyuria in diabetes insipidus?
Loss of free water
What is an alternative method of differential diagnosis for diabetes insipidus?
MRI of the pituitary and hypothalamus
What is a characteristic of hyponatremia in patients with multiple hormone deficiencies?
Low serum osmolality
What is a common neurological manifestation of hyponatremia?
All of the above
What is the normal function of ADH in the kidneys?
To decrease urine output and promote water reabsorption
What is a characteristic of transient DI?
Abrupt onset and resolution within several days
What is a physical manifestation of hyponatremia?
Decreased deep tendon reflexes
What is a complication of ADH excess?
All of the above
What is a characteristic of the permanent phase of polyuria in triphasic DI?
Gradual onset and permanent duration
What is a clinical manifestation of ADH deficiency?
Polydipsia
What is a diagnostic feature of hyponatremia?
Decreased serum Na+
What is the primary cause of hyponatremia in the Syndrome of Inappropriate ADH secretion (SIADH)?
Resorption of excessive amounts of free water
What is a neurological manifestation of ADH deficiency?
Mentation changes
What is a characteristic of triphasic DI?
Gradual onset and three distinct phases
Which of the following is a common cause of SIADH?
Small-cell carcinomas of the lung
What is a complication of ADH deficiency?
All of the above
What is the typical laboratory finding in pituitary insufficiency?
Low levels of trophic hormones
Which of the following is a neurological manifestation of SIADH?
Neurologic dysfunction
What is the primary diagnostic method for pituitary insufficiency?
Biochemical diagnosis
What is the term for the unresponsiveness of the kidneys to ADH?
Nephrogenic DI
What is the typical finding in the setting of secondary hypothyroidism?
Low free thyroxine and low TSH
What is the primary difference between SIADH and nephrogenic DI?
SIADH is caused by ADH excess, while nephrogenic DI is caused by ADH deficiency
Study Notes
Hyponatremia
- Symptoms of hyponatremia include lethargy, confusion, agitation, headache, nausea, and vomiting, and focal neurologic abnormalities
- Seizures and coma may occur with more severe hyponatremia
- Hyponatremia is present with low serum osmolality
- Daily urinary sodium excretion exceeds 20 mEq/L, despite low serum sodium levels, and urine osmolality is higher than serum osmolality
Diabetes Insipidus (DI)
- Symptoms of DI include polyuria, clear urine, urinary frequency, nocturia, weight loss, and polydipsia
- Physical manifestations include dry, cool skin, dry mucous membranes, tachycardia, fatigue, headache, anorexia, nausea, decreased mental status, seizures, and coma
- Pathophysiology: ADH deficiency diminishes kidneys' permeability to water, resulting in excretion of large volumes of hypotonic fluid
- Three patterns of DI may develop: transient DI, permanent DI, and triphasic DI
Diagnosis
- Diagnosis of DI is based on hyponatremia, low serum osmolality, and daily urinary sodium excretion exceeding 20 mEq/L
- Administration of hypertonic saline and water load test can help distinguish DI from psychogenic polydipsia
- MRI of the pituitary and hypothalamus can also aid in diagnosis
Pathophysiology of ADH Excess
- Key features of ADH excess include water retention, hyponatremia, and hypo-osmolality
- ADH causes water retention from renal tubules and collecting ducts, increasing extracellular fluid volume and dilutional hyponatremia
- Hyponatremia suppresses renin and aldosterone secretions, causing a decrease in proximal tubule reabsorption of Na+
Physical Examination and Clinical Manifestations
- Physical manifestations related to hyponatremia include decreased deep tendon reflexes, fatigue, headache, anorexia, nausea, and decreased mental status
- Physical manifestations related to fluid volume excess include weight gain without edema, jugular venous distention, tachycardia, tachypnea, and rales
Complications
- Electrolyte imbalance, hypovolemia, hypotension, shock, seizures, coma, and permanent brain damage may occur
Syndrome of Inappropriate ADH Secretion (SIADH)
- SIADH is caused by ADH excess, leading to resorption of excessive amounts of free water, resulting in hyponatremia
- The most frequent causes of SIADH include secretion of ectopic ADH by malignant neoplasms, drugs that increase ADH secretion, and central nervous system disorders
- Clinical manifestations of SIADH are dominated by hyponatremia, cerebral edema, and resultant neurologic dysfunction
This quiz covers the symptoms, diagnosis, and effects of hyponatremia, a condition characterized by low sodium levels in the blood. Learn about the signs and consequences of hyponatremia.
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