Syndrome of Inappropriate Anti-Diuretic Hormone Secretion (SIADH)

Casebank History
1

Task: Lady at GP, Talk on test results: Na low 124 Hb slight low, PMH-COPD

Paraphrase
I understand you came here for the test results, why did you have them?

Tiredness- ODIPARA

Any other symptom: Coughing blood (hidden information)- Elaborate

MAFTOSA- other causes of hyponatremia

Explain the blood test results

Checked the salts in the blood. One of the salts called sodium is quite low. This is called hyponatremia. We are concerned about your test results. You have been coughing up blood and your sodium levels are low. I am sorry to tell you cancer of the lungs (Small Cell Lung Cancer) can present this way. Unfortunately, you have developed a complication of that called SIADH.

We well request you to go the hospital immediately for correction of sodium.
Later we also need to refer you to lung specialist for suspected cancer.
Reduce Fluid Intake & Increase Salt intake.

4 Likes
2

Hyponatraemia: Summary by NICE CKS

  • Hyponatraemia is defined as a serum sodium concentration of less than 135 mmol/L.

  • It is the most common electrolyte disorder encountered in clinical practice and is usually an incidental finding on routine blood tests.

  • The severity of hyponatraemia can be classified as:

    • Mild — serum sodium concentration 130–135 mmol/L.
    • Moderate — serum sodium concentration 125–129 mmol/L.
    • Severe — serum sodium concentration less than 125 mmol/L.

  • The rate of onset of hyponatraemia can be classified as:

    • Acute — duration of less than 48 hours.
    • Chronic — duration of 48 hours or more.

  • The cause of hyponatraemia is often multifactorial. Common causes include:

    • Medications (most commonly thiazide diuretics).
    • Syndrome of inappropriate antidiuresis.
    • Underlying medical conditions (such as heart failure, kidney disease, and liver disease).

  • Most people with hyponatraemia are asymptomatic, particularly if it is mild and has developed slowly. When symptoms are present, they are often non-specific and are related to both the severity of the hyponatraemia and its rate of onset.

    • Rapid changes in serum sodium levels or severe hyponatraemia can cause symptoms of vomiting, headache, drowsiness, seizures, coma, and cardio-respiratory arrest.
    • Chronic hyponatraemia can lead to increased risk of falls, bone fractures, osteoporosis, gait instability, and concentration and cognitive deficits.

  • Assessment of a person with hyponatraemia involves taking a focused history, determining the person’s volume status, and arranging appropriate investigations (including serum and urine osmolality, and urinary sodium concentration) to help identify the cause of hyponatraemia and guide management. After the initial identification of hyponatraemia, serum sodium measurement should be repeated (timescale dependant on clinical judgement) to exclude a rapidly decreasing serum sodium concentration, which will require admission to hospital.

  • If the person has severe or symptomatic hyponatraemia, admission to hospital for urgent treatment should be arranged.

  • If the person has asymptomatic, moderate hyponatraemia, specialist advice from an endocrinologist should be sought regarding the need for admission or referral.

  • If the person has asymptomatic, mild hyponatraemia, the underlying cause of hyponatraemia should be sought in primary care (if possible and appropriate).

    • If the person has an acute illness that may be contributing to the hyponatraemia, it should be treated and the serum sodium concentration rechecked after 2 weeks.
    • Medications that may be contributing to the hyponatraemia should be stopped if appropriate and the serum sodium concentration rechecked after 2 weeks.

Secondary Care management

Secondary care management of hyponatraemia is aimed at determining and treating the underlying cause. Management strategies depend on the rate of onset of hyponatraemia, the person’s symptoms, and their volume status.

  • Acute hyponatraemia with moderate or severe symptoms:
    • Hypertonic saline restores serum sodium concentration to a safe level to correct any cerebral oedema and reduce the risk of complications.
  • Acute hyponatraemia with mild or no symptoms:
    • Non-essential parenteral fluids and medications that can provoke hyponatraemia are stopped and treatment is directed at the underlying cause.
  • Chronic hyponatraemia without moderate or severe symptoms:
    • Non-essential supplementary fluids and medications that can provoke hyponatraemia are stopped and treatment is directed at the underlying cause.
  • People with hypervolaemia:
    • Fluid restriction is recommended to prevent further fluid overload.
  • People with hypovolaemia:
    • Extracellular volume is restored with infusion of 0.9% saline.

When should I admit or refer a person with hyponatraemia?

  • Admit the person to hospital immediately if they:
    • Have acute onset (duration for less than 48 hours or severe (serum sodium concentration of less than 125 mmol/L) hyponatraemia.
    • Are symptomatic.
    • Have signs of hypovolaemia.
  • Discuss with an endocrinologist about the need for admission or referral:
    • If the person has asymptomatic, moderate hyponatraemia (serum sodium concentration of 125-129 mmol/L).
  • Arrange an urgent 2-week wait referral to the appropriate specialist:
    • If malignant disease is suspected as an underlying cause of syndrome of inappropriate antidiuretic hormone secretion (SIADH).
  • Refer to an endocrinologist, the urgency depending on clinical judgement:
    • If the cause of hyponatraemia is not clear.
    • If SIADH or another endocrine cause is suspected.
      – Hyponatraemia related to an endocrine disorder is uncommon, and will require specialist input to confirm the diagnosis and initiate treatment.
2 Likes