Diabetes insipidus (DI) is a condition characterized by excessive thirst and excretion of large amounts of severely diluted urine, with reduction of fluid intake having no effect on the concentration of the urine.
There are different types of DI, each with a different set of causes. The most common type in humans is the neurological form, called Central DI (CDI), which involves a deficiency of arginine vasopressin (AVP), also known as antidiuretic hormone (ADH).
The second common type of DI is nephrogenic diabetes insipidus (NDI), which is due to kidney or nephron dysfunction caused by an insensitivity of the kidneys or nephrons to ADH. DI can also be gestational, or caused by alcohol or some types of drug abuse. DI should not be confused with nocturia.
Although they have a common name, diabetes mellitus and diabetes insipidus are two entirely separate conditions with unrelated mechanisms. Both cause large amounts of urine to be produced (polyuria), and the term “diabetes” is derived from the Greek word meaning siphon. However, diabetes insipidus is either a problem with the production of antidiuretic hormone (central diabetes insipidus) or kidney's response to antidiuretic hormone (nephrogenic diabetes insipidus), whereas diabetes mellitus causes polyuria via a process called osmotic diuresis, due to the high blood sugar leaking into the urine and taking excess water along with it.
The incidence of diabetes insipidus in the general population is 3 in 100,000.
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).
An increase in serum sodium of ≥2.5 mmol/L is a positive marker of development of DI with 80% specificity, and a postoperative serum sodium of ≥145 mmol/L is a positive indicator with 98% specificity. Identifying perioperative risk factors and objective indicators of DI after ETSS will help physicians care for patients postoperatively 2).
Antidiuretic hormone (ADH) appears as hyperintensity (HI) in the pituitary stalk and the posterior lobe of the pituitary gland on T1-weighted magnetic resonance (MR) imaging. Its disappearance from the posterior lobe occurs with DI, indicating a lack of ADH. The appearance of HI in the pituitary stalk indicates disturbances in ADH transport.
The scarcity of studies comparing different treatment and monitoring strategies for these disorders and the lack of prior clinical guidelines makes it difficult to provide recommendations following a methodology based on grades of evidence 3).
Most patients with diabetes insipidus (DI) can drink enough fluid to replace their urine losses. When oral intake is inadequate and hypernatremia is present, replace losses with dextrose and water or an intravenous (IV) fluid that is hypo-osmolar with respect to the patient’s serum. Do not administer sterile water without dextrose intravenously, as it can cause hemolysis.
To avoid hyperglycemia, volume overload, and overly rapid correction of hypernatremia, fluid replacement should be provided at a rate no greater than 500-750 mL/h. A good rule of thumb is to reduce serum sodium by 0.5 mmol/L (0.5 mEq/L) every hour. The water deficit may be calculated on the basis of the assumption that body water is approximately 60% of body weight.
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.
Kiran et al from the Aga Khan University Hospital, Stadium Road, Karachi, Pakistan conducted a cross-sectional retrospective study on 115 patients after ethical approval. Patients were 16 years old or older undergoing pituitary or sellar surgeries. They collected data on basic sociodemographic characteristics and clinical indication for surgery. They noted laboratory values for serum electrolytes, plasma and urine osmolality, urine sodium and 24-hour fluid balance from immediate postoperative day till discharge and follow up. They recorded medical management plans. They also recorded Diabetes insipidus (DI), Syndrome of inappropriate antidiuretic hormone secretion (SIADH), cerebral salt wasting syndrome (CSW), triphasic response and hyponatremia according to the diagnostic definitions. Finally they performed data analysis on SPSS version 19.0.
Out of 115 patients there were 61.7% males, mean age 42.3 ± 13.86 years, 91.3% had pituitary adenoma (73.0% non-functioning) and 86.1% underwent transsphenoidal surgical approach. Transient DI occurred from Day 1 to 6, peaking with 57.4% on Day 2. Permanent DI and SIADH were rare. We did not note typical triphasic response and cerebral salt wasting in any of the patients. However, isolated hyponatremia occurred in 11% and 20.9% had diabetes insipidus with hyponatremia.
Transient diabetes insipidus is the most common postoperative sodium and water disturbances (SWD) after sellar, suprasellar and parasellar surgery (SSPS). Hyponatremia occurred alone and following DI. This is the first study describing postoperative sodium and water disturbances after different sellar surgeries in Pakistan 4).
Hayashi et al from the Department of Neurosurgery, Graduate School of Medical Science, Kanazawa University, Kanazawa, Ishikawa, Japan, conducted a retrospective study with 172 patients undergoing TSS for sellar tumors from 2006 to 2014. Sequential T1-weighted MR images without enhancement were evaluated for HI in the pituitary stalk and the posterior lobe to assess the localization of ADH before and at intervals after TSS. DI was assessed pre- and postoperatively. HI in the pituitary stalk showed the following morphology: (1) ovoid in the distal end of the pituitary stalk (group A), (2) linear in the distal part of the pituitary stalk (group B), (3) linear in the whole pituitary stalk (group C).
Preoperative DI occurred in 6 patients (3.5 %) with no HI observed in the posterior lobe. Postoperative DI was transient in 82 patients (47.7 %), and permanent in 11 (6.4 %). One week after surgery, HI was absent in the posterior lobe in 74 patients (43.0 %), and present in the pituitary stalk in 99 patients (57.6 %); both were significantly correlated with postoperative DI (p < 0.001). The absence of HI in the posterior lobe (A, 48.9 %; B, 68.3 %; C, 92.3 %), persistence of DI (A, 3.7 days; B, 45.9 days; C, 20.5 months), and duration until HI recovery in the posterior lobe (A, 3.6 months; B, 6.8 months; C, 22.9 months) were greatest in group C, followed by group B, and then group A. Fourteen group A patients did not have postoperative DI despite having HI in the pituitary stalk and the posterior lobe. Four group C patients developed permanent DI with persistence HI in the pituitary stalk.
HI in the pituitary stalk and its absence in the posterior lobe indicated postoperative DI, which was transient if HI was detected in the pituitary stalk. DI duration could be predicted by the length of HI in the pituitary stalk, which corresponded to the degree of ADH transport obstruction 5).
The files of 24 patients that underwent neurosurgery for sellar lesions, or tumor near the hypothalamus or pituitary gland at the Department of Neurosurgery, King Abdulaziz University Hospital, Jeddah, Kingdom of Saudi Arabia were retrospectively reviewed between January 2011 to December 2014. A total of 24 patients were studied, and were divided into 2 groups namely; DI and non-DI. Patient characteristics were studied using descriptive statistics. The differences in proportion between the 2 groups were found out using Z-test for proportion in 2 populations. The mean differences in the hormonal abnormalities for the 2 groups were assessed using independent t-test. All statistics are considered statistically significant when p less than 0.05.
During hospitalization, 13 (54.2%) out of 24 patient that underwent neurosurgery had manifestations of DI, which was transient in 5 (38.8%) and permanent in 8 (61.2%). The DI subgroup contained higher prevalence of prolactinoma, craniopharyngioma, pre-operative panhypopituitarism, and macroadenoma in MRI imaging and transphenoidal surgery. Furthermore, urine osmolality was significantly lower in the DI group post-operatively with a significant p=0.023. It was recognized that the permanent DI documented more significant numbers than other studies.
In the study group, it was recognized that permanent DI meant that our patients needed desmopressin for more than 3 months, which documented a more significant number than other studies 6).
Fifty-seven patients (mean age 55 years, 61.4% females) harbored 30 clinically hormone-inactive and 27 hormone-secreting pituitary adenomas. Postoperative WED occurred in 75.4% of the patients: in 38.5% as isolated diabetes insipidus (DI); in 21% as isolated hyponatremia; and in 15.7% as combined DI-hyponatremia. The maximum of medians of diuresis (5.750 L) in patients with isolated DI occurred on postoperative Day 2. Nadir of medians of hyponatremia (132 mmol/L) in patients with isolated hyponatremia occurred on postoperative Day 9. In patients with combined DI-hyponatremia, maximum of medians of diuresis (5.775 L) occurred on the 2nd day and nadir of medians of hyponatremia (130 mmol/L) on the 10th postoperative day. Altogether, 8.7% of the patients had to be treated with desmopressin because of DI persisting for >3 months. Of all the patients with hyponatremia, 42.8% were treated by transient fluid-intake restriction due to an IH of <130 mmol/L with or without clinical symptomatology. Transient acute renal failure occurred in one of these patients. Generally, the occurrence of postoperative WEDs was linked to the intraoperative manipulation of the neurohypophysis. Increased thirst correlated significantly with DI (p=0.001 and 0.02, respectively) and decreased thirst with the hyponatremic episode in patients with combined DI-hyponatremia (p=0.003). Decreased urine osmolality correlated significantly with the presence of DI (p=0.023). Electrolyte-free water clearance and urinary Na+ excretion were not correlated with DI and hyponatremia. Antidiuretic hormone was not suppressed during hyponatremia.
Water and electrolyte disturbances occurred in the majority of patients undergoing transsphenoidal adenomectomy and were usually transient. Diabetes insipidus is more frequent than hyponatremia. Diabetes insipidus usually occurs during the 1st postoperative day and resolves in the majority of cases within 10 days. In few patients, DI may persist and require therapy with ADH analogs. Hyponatremia usually occurs at the end of the 1st postoperative week and resolves in most cases within 5 days. Very few patients will need treatment other than fluid-intake restriction to avoid serious complications. Thus, careful monitoring of the WEDs in patients undergoing transsphenoidal pituitary adenoma surgery is mandatory for the first 10 postoperative days 7).
This clinically oriented book will familiarize the reader with all aspects of the diagnosis of tumors and other disorders of the pituitary gland by means of magnetic resonance imaging (MRI). The coverage includes acromegaly, Cushing’s disease, Rathke cleft cysts, prolactinomas, incidentalomas, Clinically nonfunctioning pituitary adenomas, other lesions of the sellar region, hypophysitis, and central diabetes insipidus. Normal radiologic anatomy and the numerous normal variants are described, and guidance is also provided on difficulties, artifacts, and other pitfalls. The book combines concise text and high-quality images with a question and answer format geared toward the needs of the practitioner. MRI is today considered the cornerstone in the diagnosis of diseases of the hypophyseal-hypothalamic region but the relatively small size of the pituitary gland, its deep location, the many normal anatomic variants, and the often tiny size of lesions can hinder precise evaluation of the anatomic structures and particularly the pituitary gland itself. Radiologists and endocrinologists will find MRI of the Pituitary Gland to be full of helpful information on this essential examination, and the book will also be of interest to internists and neurosurgeons.