A 78 year old woman with heart disease has recently been started on fluoxetine for a moderate depressive illness. She visits her GP complaining of tiredness and muscle cramps. The GP contacts you for advice, which of the following is most likely to reveal an abnormality?
| FBC | |
| Blood glucose | |
| U & E | |
| TFT | |
| CT head |
The womans history is most consistent with a diagnosis of SIADH caused by the antidepressant she has started using, this would manifest in the U & E which would show a low sodium level.
Hyponatremia
Hyponatremia (low serum sodium) in psychiatric patients may result from the psychiatric disorder itself, from its treatment, or from concomitant medical conditions.
Symptoms include:-
Where hyponatremia is drug induced it is referred to as 'the syndrome of inappropriate antidiuretic hormone hypersecretion' (SIADH) and is charcterised by excessive secretion of ADH resulting in hyponatremia and fluid overload (ADH basically dilutes the blood).
SIADH has many causes, just remember that both antidepressants and antipsychotics can cause it.
Risk factors for SIADH include:-
Jacob S et al. Hyponatremia associated with SSRIs in older adults. Ann Pharmacotherapy. 2007; 41: 411-18.
SIADH normally develops within a few weeks of starting the new drug.
Treatment usually consists of fluid restriction. In some cases demeclocycline is used.
Symptoms include:-
- Nausea and vomiting
- Confusion and lethargy
- Irritability
- Muscular spasm and cramp
- Seizures
Where hyponatremia is drug induced it is referred to as 'the syndrome of inappropriate antidiuretic hormone hypersecretion' (SIADH) and is charcterised by excessive secretion of ADH resulting in hyponatremia and fluid overload (ADH basically dilutes the blood).
SIADH has many causes, just remember that both antidepressants and antipsychotics can cause it.
Risk factors for SIADH include:-
- Being elderly
- Being female
- Being a smoker
- Having medical co-morbidity
- Polypharmacy
- Low body weight
- Low baseline sodium concentration
- Reduced renal function
- Warm weather
Jacob S et al. Hyponatremia associated with SSRIs in older adults. Ann Pharmacotherapy. 2007; 41: 411-18.
SIADH normally develops within a few weeks of starting the new drug.
Treatment usually consists of fluid restriction. In some cases demeclocycline is used.
