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Abstract：
Syndrome of inappropriate antidiuresis (SIAD) is one of the most frequent causes of euvolemic hyponatremia (serum sodium levels < 135 mEq/L) and it represents more than 35% of hyponatremia cases in hospitalized patients. It is characterized by an inappropriate vasopressin (AVP)/antidiuretic hormone (ADH) secretion, which occurs independently from effective serum osmolality or circulating volume, leading to water retention via its action on type 2 vasopressin receptor in the distal renal tubules. Corpus callosum agenesis (CCA) is one of the most common congenital brain defects, which can be associated to alterations in serum sodium levels. This report presents a rare case of chronic hyponatremia associated with SIAD in a woman with CCA, whose correction of serum sodium levels only occurred following twice-daily tolvaptan administration.
A 30-year-old female was admitted to our hospital for non-acute hyponatremia with dizziness, headache, distal tremors, and concentration deficits. She had profound hyponatremia (Na 121 mmol/L) with measured plasma hypo-osmolality (259 mOsm/Kg) and urinary osmolality greater than 100 mOsm/Kg (517 mOsm/Kg). She presented clinically as normovolemic. After the exclusion of other causes of normovolemic hyponatremia, such as hypothyroidism and adrenal insufficiency, a diagnosis of SIAD was established. We have ruled out paraneoplastic, inflammatory, and infectious causes, as well as ischemic events. Her medical history showed a CCA and frontal teratoma. We administered tolvaptan initially at a low dosage (15 mg once a day) with persistence of hyponatremia. Therefore, the dosage was first doubled (30 mg once a day) and then increased to 45 mg once a day with an initial improvement in serum sodium levels, although not long-lasting. We therefore tried dividing the 45 mg tolvaptan administration into two doses of 30 mg and 15 mg respectively, using an off-label treatment schedule, thus achieving long-lasting serum sodium levels in the low-normal range associated with a general clinical improvement.
This report underlines the importance of the correct diagnosis, management and treatment of SIAD, as well as the need for further studies about the pharmacokinetics and pharmacodynamics of vasopressin receptor antagonists.
A 30-year-old female was admitted to our hospital for non-acute hyponatremia with dizziness, headache, distal tremors, and concentration deficits. She had profound hyponatremia (Na 121 mmol/L) with measured plasma hypo-osmolality (259 mOsm/Kg) and urinary osmolality greater than 100 mOsm/Kg (517 mOsm/Kg). She presented clinically as normovolemic. After the exclusion of other causes of normovolemic hyponatremia, such as hypothyroidism and adrenal insufficiency, a diagnosis of SIAD was established. We have ruled out paraneoplastic, inflammatory, and infectious causes, as well as ischemic events. Her medical history showed a CCA and frontal teratoma. We administered tolvaptan initially at a low dosage (15 mg once a day) with persistence of hyponatremia. Therefore, the dosage was first doubled (30 mg once a day) and then increased to 45 mg once a day with an initial improvement in serum sodium levels, although not long-lasting. We therefore tried dividing the 45 mg tolvaptan administration into two doses of 30 mg and 15 mg respectively, using an off-label treatment schedule, thus achieving long-lasting serum sodium levels in the low-normal range associated with a general clinical improvement.
This report underlines the importance of the correct diagnosis, management and treatment of SIAD, as well as the need for further studies about the pharmacokinetics and pharmacodynamics of vasopressin receptor antagonists.
摘要：
■不适当利尿综合征（SIAD）是正常血低钠血症（血清钠水平<135mEq/L）的最常见原因之一，占住院患者低钠血症病例的35％以上。它的特征是不适当的加压素（AVP）/抗利尿激素（ADH）分泌，其发生独立于有效血清渗透压或循环体积，通过其对远端肾小管中2型加压素受体的作用导致水潴留。call体发育不全（CCA）是最常见的先天性脑缺陷之一，这可能与血清钠水平的变化有关。本报告介绍了一名患有CCA的女性中与SIAD相关的慢性低钠血症的罕见病例，其血清钠水平的校正仅发生在每日两次托伐普坦给药后。
■一名30岁女性因非急性低钠血症伴头晕入院治疗,头痛,远端震颤,和集中赤字。她患有严重的低钠血症（Na121mmol/L），测得的血浆渗透压浓度（259mOsm/Kg）和尿渗透压浓度大于100mOsm/Kg（517mOsm/Kg）。她在临床上表现为血容量正常。排除其他原因引起的低钠血症后，如甲状腺功能减退和肾上腺功能不全，建立了SIAD的诊断。我们已经排除了副肿瘤,炎症，和传染性原因，以及缺血事件。她的病史显示CCA和额叶畸胎瘤。我们最初以低剂量（每天一次15mg）施用托伐普坦，并持续低钠血症。因此,剂量首先加倍（每天一次30毫克），然后增加到每天一次45毫克，血清钠水平初步改善，虽然不持久。因此，我们尝试将45mg托伐普坦的给药分为30mg和15mg的两个剂量，使用标签外的治疗时间表，从而实现长期持续的血清钠水平在低正常范围与一般的临床改善。
■本报告强调了正确诊断的重要性，SIAD的管理和治疗，以及需要进一步研究血管加压素受体拮抗剂的药代动力学和药效学。
■一名30岁女性因非急性低钠血症伴头晕入院治疗,头痛,远端震颤,和集中赤字。她患有严重的低钠血症（Na121mmol/L），测得的血浆渗透压浓度（259mOsm/Kg）和尿渗透压浓度大于100mOsm/Kg（517mOsm/Kg）。她在临床上表现为血容量正常。排除其他原因引起的低钠血症后，如甲状腺功能减退和肾上腺功能不全，建立了SIAD的诊断。我们已经排除了副肿瘤,炎症，和传染性原因，以及缺血事件。她的病史显示CCA和额叶畸胎瘤。我们最初以低剂量（每天一次15mg）施用托伐普坦，并持续低钠血症。因此,剂量首先加倍（每天一次30毫克），然后增加到每天一次45毫克，血清钠水平初步改善，虽然不持久。因此，我们尝试将45mg托伐普坦的给药分为30mg和15mg的两个剂量，使用标签外的治疗时间表，从而实现长期持续的血清钠水平在低正常范围与一般的临床改善。
■本报告强调了正确诊断的重要性，SIAD的管理和治疗，以及需要进一步研究血管加压素受体拮抗剂的药代动力学和药效学。
