Syndrome of Inappropriate Antidiuretic Hormone (SIADH)

Patient presentation:
R.B., a 68 year old female, is admitted to the ED with a one month history of increased confusion and agitation. She has a history of hypertension and hypercholesterolemia.  CT of the head reveals a large enhancing mass in the occipital region. MRI of the head reveals a large butterfly lesion at the splenium of the corpus callosum.

On assessment patient is confused and mumbling words, unable to follow commands, is irritated and agitated. Pupils are sluggish and reactive. Pt scores 8 on the Glasgow Coma scale. Patient was intubated for increasing lethargy and unresponsiveness.  Repeat CT scan of the head of the head shows increasing edema, and increased intraventricular hemorrhage with developing hydrocephalus. Two ventricular drains are placed for monitoring of ICP and drainage of blood in the ventricles. ICP initially is 9-11 (normal 7 – 15 mmHg).

Two days after admission R.B.’s urine output is decreased at 15-20 cc/hr and is amber and concentrated. ICP 15-17.  BUN and creatinine are within normal limits – creatinine 0.9 and BUN 11. CVP reading taken and is 10 mmHg. Mucous membranes are moist and show no signs of dehydration.  Patient is in normal sinus rhythm, with her heart rate at baseline in low 70s.  Blood pressure is 120s/70s. Patient is started on Decadron® IV to decrease cerebral swelling.

Differential Diagnosis:
SIADH, Cerebral Salt Wasting

Diagnosis:
It is suspected that R.B. has SIADH. Labs are ordered (BMP, serum osmolarity, urine sodium, and urine osmolarity). Serum Na+ 130 mEq/L, Serum osmolarity 268 mOsm/L, urine sodium 23, Specific gravity > 1.020, urine osmolarity  >200 mOsm/L.

Because of the above lab values and pt is not hypovolemic she is diagnosed with SIADH.

Treatment:
Patient is placed on 3% NaCl at 15ml/hour, which is hypertonic sodium chloride. Patient is placed on fluid restriction, water flushes are held. BMP and serum osmolarity are checked every 6 hours.

Outcome:
R.B. responded well to therapy and 3% NaCl therapy was discontinued after 2 days. Throughout her hospital stay she showed an improvement in her mental status. She was extubated after 12 days and ventricular drains were removed after 13 days. Patient is able to say short phrases and follows simple commands. Patient was transferred to another facility for further evaluation.

What is SIADH?
SIADH is the release of ADH in excess of the physiologic need. This leads to an elevated urine osmolarity and expansion of extracellular fluid volume leading to a dilutional hyponatremia, which in some cases can lead to fluid overload (hypervolemia). SIADH can also occur with euvolemia. To differentiate between cerebral salt wasting and SIADH, they key is that cerebral salt wasting has hypovolemia and hyponatremia. Patients that are at risk of developing SIADH are those with neoplasms, CNS disorders, and pulmonary disorders.
Case created by Ronelia Balmoris, 2011.