SIADH

Table 340-3 Differential Diagnosis of Hyponatremia Based on Clinical Assessment of Extracellular Fluid Volume (Ecfv)

Clinical Findings Type I, Hypervolemic Type II, Hypovolemic Type III, Euvolemic SIAD Euvolemic History CHF, cirrhosis, or nephrosis Yes No No No Salt and water loss No Yes No No ACTH–cortisol deficiency and/or nausea and vomiting No No Yes No Physical examination Generalized edema, ascites Yes No No No Postural hypotension Maybe Maybe Maybea  No Laboratory BUN, creatinine High-normal High-normal Low-normal Low-normal Uric acid High-normal High-normal Low-normal Low-normal Serum potassium Low-normal Low-normalb  Normalc  Normal Serum albumin Low-normal High-normal Normal Normal Serum cortisol Normal-high Normal-highd  Lowe  Normal Plasma renin activity High High Lowf  Low Urinary sodium (meq unit of time)g  Low Lowh  Highi  Highi

DRUGS CAUSING SIADH:

Vasopressin or desmopressin

Chlorpropamide

Oxytocin, high dose

Vincristine

Carbamazepine

Nicotine

Phenothiazines

Cyclophosphamide

Tricyclic antidepressants

Monoamine oxidase inhibitors

Serotonin reuptake inhibitors

Q. 69-year-old man presents with confusion. His carers state that over the last month he has become increasingly lethargic, irritable and confused. Despite maintaining a good appetite, he has lost 10 kg in the last month. Blood results are as follows: Na+ 125 mmol/L, K+ 4 mmol/L Urea 3 mg/dl, Glucose (fasting) 6 mmol/L Urine osmolality 343 mmol/L. The most likely diagnosis is:
A. Hypothyroidism
B. Dilutional hyponatraemia
C. Addison’s disease
D. Acute tubulointerstitial nephritis
E. Syndrome of inappropriate anti-diuretic hormone (SIADH)

Ans: E. 



 source: Harrison principle of internal medicine,18th edition