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A 69 year old woman, a smoker for 40 years, presented with an altered taste sensation. Investigations revealed hyponatraemia with a serum sodium level of 122 mmol/l. Serum osmolality ranged between 248 and 255 mosm/kg; corresponding urine osmolality was between 430 and 835 mosm/kg. Biochemical tests of thyroid, adrenal, renal and pituitary functions were normal. Computed tomographic (CT) and magnetic resonance imaging (MRI) scans of the brain and pituitary gland were normal. Her serum sodium level returned to normal with fluid restriction. A chest radiograph showed a 3 cm spiculated opacity in the retrocardiac region. A CT scan confirmed a mass in the lower lobe of the left lung which proved to be a moderately differentiated adenocarcinoma. It revealed significant mediastinal lymphadenopathy. Mediastinoscopy failed to identify any nodal involvement. A left lower lobectomy was performed with lymph node sampling. Immediately before surgery the serum sodium level was137 mmol/l.
Her initial recovery from surgery was uneventful. However, the serum sodium levels started to fall from the fourth postoperative day and reached 117 mmol/l. She again complained of dysgeusia. Fluid restriction was commenced and her serum sodium levels recovered to 133 mmol/l with concurrent symptomatic improvement. Histopathological examination revealed a moderately differentiated adenocarcinoma, stage T2 N2 MX. At 6 weeks follow up her progress was satisfactory without any evidence of recurrence or metastasis. Her sodium values were now normal and she was symptom free.
Dysgeusia is a known manifestation of hyponatraemia.1 The association between hyponatraemia due to the syndrome of inappropriate antidiuretic hormone (SIADH) and small cell lung cancer is well known.2,3 There are strict criteria for diagnosis of SIADH,3 all of which were fulfilled in this patient. In small cell lung cancer serum sodium levels return to normal within 1–3 weeks of initiating chemotherapy in about 80% of patients.3 In our patient the levels returned to normal 2 weeks after surgery. Endocrine paraneoplastic syndromes are well documented with small cell lung cancer but are less common with other forms of lung cancers.4 This is an interesting and unusual presentation of adenocarcinoma of the lung with dysgeusia as the sole symptom.
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