Presentation
The patient presented with one week history of difficulty passing urine, constipation and back pain. The patient was found to be in a hyponatremic (sodium of 116), hypo-osomar and euvolaemic state. Serum osmolality was 154mmol/kg (low). Urine osmolality was 189mmol/kg (high). Random urine sodium was 14 mmol/L (high). The suspicion was syndrome of inappropiate antidiuretic hormine release. There were no respiratory symptoms at any stage. There was no history of smoking or family history of cancer.
Patient Data
CXR shows a round soft tissue mass in the left lower lobe. The remaining lung spaces were clear with some emphsematous changes and hyperinflation. The cardiac size was normal.
Histology revealed non small cell lung carcinoma.
Case Discussion
CXR demonstrated a round soft tissue mass in the left lower lobe. The remaining lungs were clear with some emphysematous changes and hyperinflation. The cardiac size was normal.
CT chest with contrast subsequently demonstrated lobulated heterogeneous enhancing low attenuating lesion, highly concerning for neoplasm.
A lung biopsy confirmed the diagnosis of non-small cell lung carcinoma (NSCLC).
Syndrome of inappropriate antidiuretic hormone secretion (SIADH) occurs due to unsuppressed anti-diuretic hormone secretion, resulting in impaired water excretion. Barrter and Schwartz's criteria for SIADH include:
decreased serum osmolality (<275 mOsm/kg),
increased urine osmolality (>100 mOsm/kg),
euvolemia, and
increased urine sodium (>20mmol/L).
Causes of SIADH include drugs, central nervous system pathologies impacting the pituitary gland (stroke, infection, trauma), malignancies, post-surgical status, pneumonia and others 1.
In this case, biopsy was performed and non-small cell lung carcinoma was diagnosed.
Non-small cell lung carcinoma is a subset of lung cancer and can be further categorized histologically into three main types: adenocarcinoma, squamous cell carcinoma and large cell carcinoma. It may present with cough, hemoptysis, chest pain, dyspnea or hoarseness and features of bone or brain metastases may be present. Risk factors include smoking, alcohol use, environmental exposure (asbestos, second-hand smoke, arsenic), radiation therapy, human immunodeficiency virus infection and pulmonary fibrosis 2 . It has been suggested that ectopic release of ADH leads to SIADH in malignancy. SIADH is a rare occurrence in NSCLC, with an incidence of only 2-4% 3.
Therefore, in cases with hyponatremia and suspected SIADH it is important to assess for a variety of causes including malignancy with a paraneoplastic syndrome.
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