ADH分泌異常症候群—脳腫瘍術後発生した自験例を中心として

A Case of Syndrome of Inapropriate Secretion of Antidiuretic Hormone with Positive ADH Bioassay

I．はじめに

　"Salt-wasting"syndromeは以前から知られていたが^1）2）3），これに抗利尿ホルモンADHの分泌異常に基つく場合があることが明らかになつたのは、Schwartzら^4）5）の報告以来である。すなわち水分摂取が続けられているときに，ADHの分泌がそれに見合つて減少しないため，水分の体内蓄積が起こり，祖対的な低Na （ナトリウム）血症となる（dilutional hyponatremia）二次性に尿中Na排泄の増加があるため（sodium depletion）低Na血症はさらに進行する。水分の過剰蓄積は古くから知られている水中毒^6）を招き，けいれん，昏睡などをひき起こす。

　ADH分泌異常症候群ISyndrome of Inappropriate Secretion of Antidiuretic Hormone^7），以下SIADHと略す）は気管支癌その他の胸腔内疾患や，中枢神経系疾患などで広く報告されており（第1表），本邦でも吉利ら^8）のsarcoにdosisの1例や，最近では中尾ら^9）の気管支癌の1例が報告されている。われわれは6歳男児の脳腫瘍開頭術後において，本症と思われる状態を経験し，かつ血中ADHの測定によりinappropriate secretionの序在を直接に示唆する所見を得た。本自験例を中心として，SIADHに考察を加える。

Status epilepticus and marked hyponatremia (se-rum Na 100mEq/L) was noted on a six-year-old boy who had undergone left suboccipital craniectomy for partial excision of the intracerebellar tumor 21 days prior to this episide. Post-mortem examina-tion later revealed the tumor as glioblastoma multi-forme extending along the brain stem, completely replacing the hypothalamus and infiltrating the an-terior and posterior lobes of the pituitary gland.

Routine laboratory examinations, various endocrine tests, and water and electrolyte balance studies were compatible with the cardinal findings of Syndrome of Inappropriate Secretion of Antidiuretic Hormone or SIADH proposed by Bartter and Schwartz⁷⁾ in 1967. Water loading test demonstrated the consis-tently elevated urine osmolality over that of serum.

Serum ADH (arginine vasopressin) concentration was bioassayed after the method of Yoshida et al.⁴⁷⁾ and was noted to be inappropriately high, that is, 1.0 μU/ml when overhydrated or during water load-ing test and 1.4 μU/ml two hours after breakfast with the serum sodium concentration being 125 mEq/l.

There was noted abnormally elevated serum fluoro-cortisol, responding moderately to β^1-24 ACTH sti-mulation but only weakly to dexamethasone sup-pression. No explanation is offered to this fact ex-cept for the presumption that the equivalent mecha-nism as that of ADH might be working on the ACTH secretion from the hypothalamic-anterior pituitary complex.

The pathophysiology of the SIADH and the similar conditions were discussed in detail.