tremia due to SIADH in a patient with ... SIADH can develop as the result of many
different disease ... exceeds the urine output, the ensuing water retention.
Vol. 9, No: 2 July - Dec 2013. Page 1 - 44
Amrita Journal of Medicine
CASE REPORT
Lung Cancer Presenting as Hyponatremia Vishnu Dev U*, Sreedharan S***, Bindhu M.R**, Mathew A***, Rajesh R***, Kurian G***, V. N Unni*** ABSTRACT SIADH is a disorder of water balance characterised by hypotonic hyponatremia and impaired urinary dilution in the absence of renal disease or any identifiable physiological stimulus known to release vasopressin. SIADH can develop as the result of many different disease processes that disrupt the normal mechanisms that regulate vasopressin secretion. We report a patient with SIADH due to an underlying small cell lung cancer.
INTRODUCTION The syndrome of inappropriate antidiuretic hormone secretion (SIADH) is a condition characterised by hyponatremia and hypo-osmolality of plasma resulting from inappropriate secretion or action of the hormone leading to impaired water excretion, despite increased plasma volume1. We report an interesting case of chronic hyponatremia due to SIADH in a patient with small cell lung cancer. CASE REPORT A 61 year old male presented to our institution with generalised weakness and fatigue of eight months duration. He has had multiple hospital admissions in different hospitals during these eight months for generalised weakness, irrelevant talk, alteration in sensorium and two episodes of convulsions. He was found to have hyponatremia. However, the etiology remained elusive and was given parenteral 3% saline on numerous occasions. The patient also had weight loss of about 8 kgs in the last few months. Physical examination revealed pallor and stable vital signs. Systemic Examination was unremarkable. Investigations revealed a normocytic normochromic anaemia(Hb-9.2gm%), normal leucocyte counts(8,220/ cu.mm) and platelets(2,75,000/ cu.mm). Blood sugars, renal function tests and liver function tests were normal. Urine examination did not reveal proteinuria or microscopic haematuria. *Dept. of Internal Medicine, ** Dept. of Pathology, *** Dept. of Nephrology,
Serum potassium (3.5 mEq/L), calcium (8.1mg/dl) and uric acid (3.4mg/dl) were normal. Serum sodium was 124mEq/L, urine osmolality-753.8mOsm/kg, urine sodium-165.6mmol/l, plasma osmolality-261.8mOsm/kg and 24-hour urinary sodium was 168.8mmol/day.The thyroid function tests (free T4-1.3ng/ dl, TSH-0.5uIU/ml) and fasting cortisol (14.3ug/dl) were normal. A diagnosis of chronic hyponatremia due to SIADH was made. ECG, X-Ray Chest and CT brain were normal. A high resolution CT scan of the chest with contrast revealed a soft tissue density mass involving the left para-aortic, para-tracheal and right hilar region, which was encasing the left pulmonary artery causing an extrinsic compression (Figure1).
opsy was done, which revealed a small cell lung carcinoma (Figure 2a,2b). The patient was treated with Etoposide and Carboplatin. Subsequently, the sodium levels improved and the patient became symptomatically better.
Figure 2a : Transbronchial biopsy of the mass showing a neoplasm composed of cells in sheets (infiltrating between native glands) with scanty cytoplasm, high N/C ratio, nuclear moulding and increased mitoses (40X).
Figure 1 : CT chest showing the soft tissue density mass encasing the left pulmonary artery (arrow).
Bronchoscopy showed mucosal involvement and extrinsic compression of the left upper lobe bronchus. The mucosal surface was irregular, friable and bleeding on touch. A transbronchial bi-
Figure 2b : IHC for Synaptophysin (40X) – showing cytoplasmic positivity which confirms the neuro-endocrine nature.
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Amrita Journal of Medicine
Lung Cancer Presenting as Hyponatremia
DISCUSSION The syndrome of inappropriate secretion of antidiuretic hormone (SIADH) is a disorder of impaired water excretion caused by the inability to suppress the secretion of antidiuretic hormone (ADH). If water intake exceeds the urine output, the ensuing water retention leads to the development of hyponatremia. Antidiuretic hormone (ADH or arginine vasopressin) secretion results in a concentrated urine and therefore a reduced urine volume. The higher the plasma ADH, the more concentrated the urine. In most patients with SIADH, ingestion of water does not adequately suppress ADH and the urine remains concentrated. This leads to water retention and increase in total body water. This increase in the total body water lowers the plasma sodium concentration by dilution. In addition, the increase in total body water transiently expands the extracellular fluid volume and thereby triggers increased urinary sodium excretion; this is an attempt to bring the extracellular fluid volume towards normal and further lowers the plasma sodium concentration. Hyponatremia (serum Na+
