Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) due to Lung Cancer and Aspiration Pneumonia

Author: V. Dimov, M.D.
Reviewer: S. Randhawa, M.D.

A 56-year-old Caucasian female (CF) who is treated at a skilled nursing facility (SNF) for aspiration pneumonia and squamous cell cancer (SCC) of the lung with brain metastases is admitted to the hospital with increasing shortness of breath (SOB). The chest X-ray (CXR) and the CT scan of the chest show a lung mass and increasing infiltrates.

Physical examination

Emaciated patient, visibly SOB.
Vital signs: 37.2-110-20-140/70-SpO 92% on 2 L/min nasal cannula (NC).
Chest: (B) crackles.
CVS: Clear S1S2.
Abdomen: cachectic, +BS, NT, ND.
Extremities: no c/c/e.

Laboratory results


Typical laboratory findings in Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) (click to enlarge the images).

What is the reason for hyponatremia?

The most likely reason is Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH).

What labwork would you order to diagnose Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH)?

- BMP
- Plasma osmolality
- Plasma uric acid
- Urine sodium
- Urine osmolality

What happened?

The arterial blood gas (ABG) analysis showed hypoxemia. The patient was placed on higher flow O2. ABG 30 minutes later showed resolution of hypoxemia. Blood cultures were drawn. Vancomycin was added. The patient is at risk for Pseudomonas due to structural lung disease (lung cancer) and MRSA (hospital stay).

The laboratory results confirmed a typical case of SIADH.

Diagnostic criteria for Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) include the following:

- Hyponatremia (serum sodium less than 135 mEq/L)
- Hypotonicity (plasma osmolality less than 280 mOsm/kg)
- Inappropriately concentrated urine (more than 100 mOsm/kg water)
- Elevated urine sodium concentration (more than 20 mEq/L), except during sodium restriction
- Clinical euvolemia
- Normal renal, adrenal, and thyroid function

Final diagnosis

Syndrome of Inappropriate Antidiuretic Hormone Secretion (SIADH) due to Lung Cancer and Aspiration Pneumonia

References

Syndrome of Inappropriate Antidiuretic Hormone Secretion. eMedicine.
Hyponatremia. NEJM 2000.
Hypernatremia. NEJM 2000.
Recurrent Aspiration Pneumonia. NEJM Images in Clinical Medicine, 11/2008.

Related reading

Lowest sodium I have ever seen http://goo.gl/QgJmf

Published: 05/28/2007
Updated: 10/18/2010

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