Definition
An excess of endogenous ADH, either cerebral or tumour derived (as a paraneoplastic syndrome)
Presentation
Usually an incidental finding on biochemical investigations, but may present with features of hyponatraemia
Examination
Patients will usually be euvolaemic
Bedside tests
Laboratory investigations
Bloods
U&Es
Renal function is usually normal
Serum osmolality - <270-280mmol/kg
Urine
Urine electrolytes - Urine [Na+] > 40mmol/L
Urine osmolality will be inappropriately high (100>mmol/kg)
Radiological investigations
Differential diagnosis
Tumours
Prostate
CNS disorders
Trauma
Meningitis / Meningoencephalitis
Pulmonary disorders
Abscess
Drugs
Anticonvulsants (eg carbamazepine)
Antipsychotics (eg haloperidol)
Antidepressants (eg amitriptyline, fluoxetine)
Cytotoxics (eg cyclophosphamide, vincristine)
Opiates (eg morphine)
Thiazides
Prolonged stress, nausea, pain (eg post-operative)
Idiopathic