A 35 year old man presents with vomitings and confusion. On examination Na+ 120 m mol/L, K+ 4.2 m mon, Uric acid 2 mg/dl. Patient is not edematous. The diagnosis is:

Answer is A (Cerebral toxoplasmosis with SIADH): The patient in question satisfies all the diagnostic features of SIADH, leaving no doubt as regards the diagnosis. Laboratory parameters in patient Normal values SIADH CRITERIA 1. Serum Na.: 120 mmol/1 i.e. Hyponatremia (137-145 mmol/1) < 135 mmol/1 2. Uric acid: 2 mg/dl i.e. Hypouricemia 2.5-8.5 mg/dl < 4 mg/di 3. Serum ICI': 4.2 mmol i.e. Normokalemia 3.5-4.5 mmol/1 3.5-4.5 mmol/1 Edema does not occur in SIADH despite hypervolumia. The patient in question has distinctly been mentioned as 'non edematous', thus providing us with an impoant lead to the answer.