特発性正常圧水頭症とアルツハイマー型認知症の鑑別におけるeZISの有用性

Differentiation of Idiopathic Normal Pressure Hydrocephalus from Alzheimer's Disease Using Easy Z-score Imaging System (eZIS)

抄録

　特発性正常圧水頭症（idiopathic normal pressure hydrocephalus，iNPH）は，20数年前，治療可能な認知症（treatable dementia）として注目されたが，シャント手術の成績がよくなかったことよりあまり省みられなくなった。しかし，2004年に診療ガイドラインが作成され，今再び注目を集めている。特徴的な臨床所見や頭部MRI画像を示す典型例は診断が容易であるが，iNPHでも歩行障害が明らかでない症例，またアルツハイマー型認知症（AD）でも脳室の拡大が顕著な症例も存在し，このような場合にはその鑑別に苦慮することもしばしば経験する。iNPHとADの鑑別をさらに向上させるために，脳血流SPECTのe-ZIS（two tail view）所見に注目し，特徴的な所見が得られたので報告する。

　Idiopathic normal pressure hydrocephalus (iNPH) is characterized by the clinical triad of cognitive impairment, gait disturbance, urinary incontinence, and ventricular enlargement with normal cerebrospinal fluid (CSF) pressure. In iNPH cases that do not present some of these characteristic symptoms, it is difficult to distinguish between iNPH and other medical conditions such as Alzheimer's disease (AD). In order to increase the accuracy of the clinical diagnosis of iNPH, we performed ^99mTc-ethylcysteinate dimer (ECD) brain perfusion single photon emission computed tomography (SPECT) and analyzed the results using an easy Z-score imaging system (eZIS). Thirteen patients diagnosed with iNPH on the basis of the diagnostic guideline (8 definite and 5 probable) and 10 probable AD diagnosed according to the NINCDS-ADRDA with prominent ventriculomegaly underwent ECD-brain perfusion SPECT. A two-tail view of analysis eZIS demonstrated a distinct two-layered structure with decreased blood flow in the cingulate gyrus and enhanced perfusion in the exterior region of this layer in the sagittal view in iNPH, cases：however, similar findings could not be observed in AD cases. The possible explanation for such a finding with respect to iNPH cases could be the insufficient anatomical standardization of SPECT images and consequent false-positive result observed as hypoperfusion in the cingulate gyrus in the two-tailed view of eZIS analysis due to the marked enlargement of the ventricle. Enhanced blood perfusion at the outer layer of the hypoperfusion area was caused by increased RI count per volume due to the exclusion of the cerebral cortex by the dilated ventricle. Our results suggest that two-tail view of brain perfusion SPECT using eZIS analysis could prove to be a useful support tool for the diagnosis of iNPH.