Hyponatraemia in a neurosurgical patient: syndrome of inappropriate antidiuretic hormone secretion versus cerebral salt wasting

ficant for neurological findings. He was lethargic, disIntroduction oriented to person, place, and time, and had increased tremulousness. Cranial nerves II–XII were intact. Hyponatraemia is a common electrolyte disorder in Muscle strength was 5/5 throughout. Reflexes were the setting of central nervous system disease and is 2+ and symmetrical and the Babinski sign was negaoften attributed to the syndrome of inappropriate tive bilaterally. Initial laboratory examination was secretion of antidiuretic hormone (SIADH). This synunremarkable. A CT scan of the head without contrast drome is characterized by hyponatraemia with an showed evidence of a subarachnoid haemorrhage with inappropriately concentrated urine, increased urine extra axial haemorrhage adjacent to both frontal lobes. sodium concentration, and evidence of normal or A cerebral angiogram was normal with no evidence of slightly increased intravascular volume. By contrast, aneurysm or vascular malformation. there are patients with intracranial disease who develop The patient was transferred to Parkland Memorial hyponatraemia with similar characteristics but differ Hospital and admitted to the neurosurgery service. He in that there is clinical evidence of a contracted extrawas treated with librium for his tremulousness, dilantin cellular fluid (ECF) volume. This form of hyponatraefor seizure prophylaxis, and thiamine, folate and multimia is due to excessive renal sodium excretion resulting vitamins. Over the following days his mental status from a centrally mediated process and is termed cerebimproved to baseline. ral salt wasting (CSW ). While fluid restriction is the On hospital day 10 the patient was noted to be treatment of choice in SIADH, the treatment of CSW confused and hypotensive. His physical examination consists of vigorous sodium and volume replacement. was notable for orthostatic changes in pulse and blood pressure. The following data was obtained (mmol/l ): Given the divergent nature of the treatment and the Na 118, K 5.2, Cl 85, 3 22. Other laboratory tests potential for improper selection of fluid therapy to obtained showed a serum creatinine concentration of worsen the underlying clinical condition it is of para0.8 mg/dl, glucose 88 mg/dl, and a serum osmolality mount importance for the clinician to be able to of 258 mosm/l. The uric acid was 3.4 mg/dl. Tests of recognize and differentiate between these two entities. both thyroid and adrenal function were normal. Urine electrolytes showed (mmol/l ): Na 204, K 20, Cl 191. The urine creatinine concentration was 71 mg/dl and Case the urine osmolality was 633 mosm/l. In summary, this 44-year-old man developed sigA 44-year-old black man was admitted to an outside nificant hyponatraemia in association with a recent hospital after a fall with loss of consciousness. His subarachnoid haemorrhage. Two potential causes of past medical history was significant for chronic alcoholhyponatraemia in this setting are SIADH and CSW. ism complicated by alcohol withdrawal seizures and Distinguishing between these disorders will be the delirium tremens. On physical examination, the patient primary focus of this review. To better understand was found to be a thin black man who appeared older how these disorders differ from other causes of hyponathan his stated age. Vital signs showed: temperature traemia, a brief overview on the general approach to 98.6°F, heart rate 100/min, respiratory rate 18/min, the hyponatraemic patient will be provided. For a BP 140/60 mmHg without orthostatic changes. The more detailed discussion on this topic, the reader is remainder of the physical examination was only signireferred to two recent reviews [1,2].