An unusual case of resistant hyponatraemia in a patient with a large sellar tumour.
C Feeney, A DeSilva, O Chaudhri, E Hatfield, K Meeran
Department of Endocrinology, Charing Cross and Hammersmith Hospitals, Imperial College Healthcare NHS Trust, London, W6 8RF
We present a case of a 29 year-old male from Ethiopia who presented on arrival to the UK with marked visual loss bilaterally, headache, systemic upset and significant hyponatraemia (115 mmol/L). MRI brain imaging demonstrated a large, lobulated, sellar and suprasellar mass, elevating the floor of the 3rd ventricle and compressing the optic chiasm. Pituitary profile on admission was as follows: FSH <0.5 IU/L, LH 0.1 IU/L, testosterone 0.9 nmol/L, TSH 0.66 mU/L, T4 6.8 pmol/L, ACTH 13 ng/L, IGF1 6.7 nmol/L, prolactin 90mU/L. A random evening cortisol was 406 nmol/L. Plasma osmolality was 242 pOsmol/kg paired with a urine osmolality of 601pOsmol/kg. Hydrocortisone (50mg qds) and thyroxine (50 µg od) was commenced prior to transfer to the neurosurgical centre at Charing Cross Hospital.
On admission, repeat biochemistry was as follows: Na 122 mmol/L, serum osmolality 245 pOsmol/kg, urine osmolality 527 pOsmol/kg, urine sodium 158 mmol/L. The patient was assessed as being euvolaemic and so assigned a provisional diagnosis of SIADH. Fluid restriction to 500mls oral intake/24hrs for 5 days failed to make any improvement on plasma sodium levels and initially worsened them. Despite this, the patient continued to make relatively large volumes of urine (1l-3.5l/24hrs) with sodium concentrations consistently over 100 mmol/L. A hypovolaemic state ensued which widened the differential diagnosis to include cerebral salt wasting syndrome (CSWS). Salt depletion was initially replenished using isotonic saline (0.9%), but later required hypertonic saline (1.8%), oral sodium and fludrocortisone to augment sodium levels to a maximum level of 128 mmol/L prior to surgery.
The patient underwent a transphenoidal resection of the mass followed by a debulking procedure via craniotomy one week later. Histology demonstrated a sellar neuroblastoma. 4 months post neurosurgery and radiotherapy, plasma sodium levels have improved (latest 132 mmol/L) but urine osmolalities are still high (latest 669 pOsmol/kg).
CSWS is a recognised, but debated, clinical entity distinguishable from cranial SIADH on the basis of a reduced plasma volume. Hypovolaemia in this case, as evidenced by ongoing negative fluid balance, combined with marked renal salt loss lead us to designate a diagnosis of CSWS.