Syndrome of Inappropriate ADH (SIADH)

Syndrome of Inappropriate ADH (SIADH)

Pathology:                    Inappropriate anti-diuretichormone secretion leading to water retention and relative hyponatraemia.


Aetiology:                     Idiopathic

                                          Endocrine:Hypothyroidism, Addison’s Disease

Ectopic Production:Small cell lung cancer, pneumonia, abscess, TB

Malignancy: Lung,pancreas, ovary, lymphoma, thymoma

CNS: Tumour,trauma, infection, strike, multiple sclerosis, Guillain-Barre

         Syndrome,meningitis, encephalitis, subarachnoid haemhorrhage

Drugs: SSRIs,TCAs, opiates, haloperidol, MAOIs, diuretics, NSAIDs


Symptoms:                   Fatigue, confusion, falls,seizures, inappropriate thirst, headache, nausea


Signs:                              Weakness, coma,euvolaemia, papilloedema, myoclonus, ataxia, tremor


Investigations:          Bloods:U&E – hyponatramia, serum osmolarity, TFTs and Cortisol

 MSU: Urinarysodium (raised) and osmolarity

 Imaging: CT headto assess for malignancy

Treatment:                  Fluid restriction, Demeclocycline


Complications:         Central pontinemyelinolysis with rapid correction; to prevent this a sodium

correctionrate of 0.5-1mmol/hour should be used


Prognosis:                    Usually good for idiopathicor drug related causes


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