A 53-year-old woman refused surgery for severe trigeminal neuralgia. She was treated with carbamazepine and the symptoms were under control. A couple of weeks later she is brought to the emergency in a disoriented state. Her son says that she has been complaining of nausea, increasing thirst and balancing difficulties since a few days. On examination, she does not have any signs of dehydration or heart failure. Her blood pressure is 120/80 and pulse rate is 80/mt. Investigations reveal normal blood counts, chest X-ray and ECG.
Serum sodium level is 125 mmol/L, potassium 4.3 and normal serum creatinine, urea and uric acids. Other investigations are normal including urine analysis, hormonal work up and imaging studies. What is the probable diagnosis? Source: van der Lubbe et al. NDT Plus. 2009 Nov;2(Suppl_3):iii20-iii24.
