The most common type in humans is the neurological form, called (central diabetes insipidus) (CDI), which involves a deficiency of arginine vasopressin (AVP), also known as antidiuretic hormone (ADH).
Also called neurogenic diabetes insipidus. It is also known as neurohypophyseal diabetes insipidus referring to the posterior pituitary (neurohypophysis), which is supplied by the hypothalamus in the brain. This condition has only polyuria in common with diabetes and although not mutually exclusive, with most typical cases, the name diabetes insipidus is a misleading misnomer.
A better name might be “hypothalamic-neurohypophyseal ADH deficiency”.
Postoperative diabetes insipidus (DI) is a significant cause of morbidity in craniopharyngiomas.
Central DI is observed in 16-34% of patients recovering from sellar region operations and is generally transient; however, this condition may increase the length of hospitalization, as well as cause morbidity after pituitary surgery. In addition, DI can lead to severe hypernatremia if the fluid is not instantly replenished. Hence, monitoring for DI is essential during the first post-operative days; correspondingly, accurate diagnosis followed by correct treatment is crucial 1).
The most frequent cause of CDI are central nervous system tumors (CNS) including craniopharyngioma and germ cell tumors, which could damage the AVP neuron system. CDI is also caused by inflammatory diseases such as lymphocytic infundibulo neurohypophysitis (LINH) and IgG4-related disease. CDI often manifests after pituitary surgery. In this case, polyuria appears in the first 2 days after surgery and sometimes resolves spontaneously, although it could persist permanently if AVP neurons are damaged substantially.
In patients with central DI, desmopressin is the drug of choice.
A synthetic analogue of antidiuretic hormone (ADH), desmopressin is available in subcutaneous, IV, intranasal, and oral preparations.
Generally, it can be administered 2-3 times per day. Patients may require hospitalization to establish fluid needs. Frequent electrolyte monitoring is recommended during the initial phase of treatment.
Alternatives to desmopressin as pharmacologic therapy for DI include synthetic vasopressin and the nonhormonal agents chlorpropamide, carbamazepine, clofibrate (no longer on the US market), thiazides, and nonsteroidal anti-inflammatory drugs (NSAIDs). Because of side effects, carbamazepine is rarely used, being employed only when all other measures prove unsatisfactory. NSAIDs (eg, indomethacin) may be used in nephrogenic DI, but only when no better options exist. In central DI, the primary problem is a hormone deficiency; therefore, physiologic replacement with desmopressin is usually effective. Use a nonhormonal drug for central DI if response is incomplete or desmopressin is too expensive.
A 42-year-old white man was referred to neurosurgery due to a nonfunctioning pituitary macroadenoma. He underwent a partial resection of the tumor on July 2, 2015. On the day following surgery he presented polyuria with sodium 149 mEq/L, plasma osmolality 301 mOsm/kg, and urine osmolality 293 mOsm/kg. He started nasal desmopressin 0.05 mg/day with good response. He was already on dexamethasone 4 mg and levothyroxine 75 mcg due to hypopituitarism after surgery. On July 9 he became confused. Cerebral computed tomography was performed with no significant changes. His natremia dropped to 128 mEq/L with development of polyuria despite maintenance of desmopressin dose. His hemoglobin and hematocrit rose from 9.1 g/L to 11.6 g/L and 27.5 to 32.5, respectively. His thyroid function was normal and he was on hydrocortisone 30 mg/day. At 12 p.m. 150 mg/hydrocortisone infusion was initiated, but sodium did not increase. Plasma and urine osmolality were 264 mOsm/kg and 679 mOsm/kg, respectively. At 4 p.m. hydrocortisone was increased and hypertonic saline replacement started. Two hours later he was dehydrated with polyuria and vomiting, and natremia of 124 mEq/L. Hyponatremia was very resistant to treatment despite hypertonic saline replacement, hence desmopressin was suspended. The following day, urine spot analysis showed that natriuresis was 63 mEq/L with serum sodium 132 mEq/L. This was interpreted as a cerebral salt wasting syndrome and control was achieved with aggressive hypertonic saline replacements and fludrocortisone 0.1 mg/three times a day.
Costa et al., from the Centro Hospitalar de São João, Porto, Portugal, present a rare case of a patient with diabetes insipidus and cerebral salt wasting syndrome, who was successfully treated. Hyponatremia in a patient with diabetes insipidus may erroneously be interpreted as inadequate diabetes insipidus control or as syndrome of inappropriate antidiuretic hormone secretion, leading to therapeutic errors. Thus, all clinical and analytical data should be evaluated together for early and correct diagnosis 2).