SIAD
refers that the hyponatremia and hypo-osmolality resulting from inappropriate,
continued secretion or action of the ADH hormone despite of normal or increased
plasma volume, which result in impaired water excretion.
We
know ADH is secreted from posterior pituitary gland & responsible for concentrated
urine. When the osmolality of the body increase, ADH is secreted and acts on
the V2 receptors of the collecting tubules of the kidneys and helps
to reabsorb free water from the renal medulla. But in SIAD, ADH is secreted inappropriately
and causes more water reabsorption and the Na+ concentration in the ECF become low . The
Condition became Hypotonic and Hyponatremic which is the main effect of SIAD.
Types:
1.
Acute
2.
Chronic – in cancer patients it may be chronic.
Causes of SIAD: SIAD may be occurs due to –
A. Increased secretion of ADH:
CNS: Stroke, hemorrhage, Infection,
trauma, psychosis, Pituitary tumors,porphyria
Pulmonary conditions: Pneumonia,
Tuberculosis, acute respiratory failure, Asthma, Atelectasis
Drugs: Cyclophosphamide , vinccristine
,Amiodarone, Ciprofloxcacine ,Antipsycotic drugs ,SSRIs ,TCAs,
MAOIs,Bromocriptine
, Carbamasepine.oral hypoglycemic agents ,
Postoperative state: Major
abdominal operation, Thoracic surgery
B.
Ectopic secretion of ADH:
Lung
cancers, tumor of duodenum & pancreas, Thymus tumor, Sarcoma, Malignant
histiocytosis ,mesothelioma ,Olfactory
neuroblastoma ,
C.
Increase sensitivity to ADH: NSAIDs , Cyclophosphamide ,
tolbutamide , carbamazepine,
Chlorpromide.
D.
Miscellaneous : Exogenous administration of vasopressin
,malnutrition , Cachexia ,AIDS
Diagnosis:
SIAD
is a diagnosis of exclusion, it is necessary to rule out the
thyroid,renal,liver ,cardiac, adrenal
Dysfunction
through laboratory testing.
Markers are
a. Low plasma sodium concentration (<130 mmol/L)
b . Low plasma osmolality (<270 mmol/kg) {normal 300
mmol/kg }
c. Urine osmolality not minimally low (>150 mmol/kg)
d.Urine sodium concentration not minimally low ( > 30
mmol/L )
e. Low normal plasma urea , creatinine ,uric acid
[a,b,c,d,e taken from Davidson’s Principles and practice
of medicine 22nd edition ]
Sign /Symptom
If hyponatremia occurs gradually:
·
Asymptomatic
·
Anorexia
·
Nausea
·
Vomiting
·
Irritability
·
Headache
·
Abdominal cramp
If
Hyponatremia occurs rapidly:
·
Sign of cerebral
oedema my developed
·
Headhache
·
Nausea
·
Muscle cramps
·
Generalized weakness
·
Hyporeflexia
·
Confusion,coma
·
Seizures
Treatment:
Before treatment others cause of hyponatremia must be
excluded
- If asymptomatic hyponatremia only fluid restriction may improve gradually (600 -1000 ml/day)
- If mild symptomatic hyponatremia loop diuretics may be added except thiazide with fluid restriction.
- If sever hyponatremia infusion must be first choive but correction must not more than 10 mEq/L/day. Because if it corrected more than 10 mEq/L/day demyelination syndrome may develop.
- Vasopressin receptor antagonist may be used such as tolvaptan.
Collected
& Concise only for postgraduate student
