尿細管性アシドーシス1型に浸透圧性脱髄症を合併し，橋出血を伴う多彩な画像所見を呈した1例

Pontine Hemorrhage in a Patient with Type 1 Renal Tubular Acidosis Associated with Osmotic Demyelination Syndrome

はじめに

　浸透圧性脱髄症（osmotic demyelination syndrome：ODS）は，central pontine myelinolysis（CPM）とextrapontine myelinolysis（EPM）とを総称した疾患概念であり，浸透圧や電解質の急激な変化に伴い，橋あるいは基底核の浮腫および脱髄を呈する疾患である^1）。アルコール中毒や栄養不良，糖尿病，肝疾患，熱傷などの基礎疾患を有する患者に，低ナトリウム血症の補正や高浸透圧が加わることで発症することが多い。尿細管性アシドーシス（renal tubular acidosis：RTA）1型では，しばしば低カリウム血症を呈するが，ODSを合併した報告は少ない^2，3）。RTA1型の治療経過中にODSを合併し，橋の出血性変化を伴う多彩な画像所見を呈した症例を経験したので報告する。

Abstract

　Here, we report the case of a 23-year-old man with type 1 renal tubular acidosis (RTA) associated with osmotic demyelination syndrome (ODS) who developed pontine hemorrhage.　Acute progressive tetraparesis had developed during the clinical course of the RTA.　Neurological examination revealed bilateral weakness in all 4 limbs associated with severe hypokalemia (K 1.4 mEq/L).　He experienced a sudden onset of general convulsions and mutism during the treatment for metabolic acidosis and hypokalemia.　The T2-weighted MR image of the brain revealed multiple hyperintense signal lesions in the central pons as well as in the extrapontine sites of the bilateral cortical and subcortical areas in the frontal and parietal lobes.　A T2-star (T2^＊) -weighted MR image showed focal hemorrhagic lesions in the lower pons.　On the basis of the diagnosis of ODS, he underwent corticosteroid and thyrotropin-releasing hormone therapy, after which his neurological signs and symptoms have gradually reduced.　While analyzing the possible etiology, it has been suggested that osmotic vascular injuries induced by elevated levels of serum potassium and osmolarity give rise to edema and vascular endothelial damage; these conditions, consequently lead to hemorrhagic necrosis.　Physicians need to be aware that RTA patients may develop ODS after hypokalemia, and the potassium levels need to be corrected carefully.

(Received: November 6, 2007, Accepted: June 11, 2008)