前方型痴呆の病理

Neuropathology of anterior type dementia

限局性の脳萎縮を示す前方型痴呆（ピック病）は，ピック小体病とユビキチン封入体（UI）を伴う葉性萎縮に分かれる。本邦では両者はほぼ同数存在する。ピック小体病とUIを伴う葉性萎縮の大脳や，皮質下神経核の変性・萎縮パターンは共通しており，脳萎縮は高度に至る。ピック病の脳萎縮にはバリエーションがあり，約半数が萎縮の左右差を示す。右側優位萎縮よりも左側優位萎縮が多い。萎縮脳葉，部位にもバリエーションがあり，本邦では欧米に較べて，前頭葉優位萎縮よりも側頭葉優位萎縮例が多い。ピック小体病では運動ニューロン系は冒されないが，UIを伴う葉性萎縮は種々の程度に上位運動ニューロン（錐体路）変性を来すことがある。びまん性の脳萎縮を示す前方型痴呆には，MNDを伴う痴呆，皮質基底核変性症（前頭葉萎縮群），好塩基性封入体病，進行性皮質下グリオーシス，FTDの前頭葉変性型が含まれる。これらの疾患ではピック病のような限局性脳萎縮を示さず，萎縮の程度も好塩基性封入体病以外は軽度にとどまる。

Anterior type dementia, which is characterized by circumscribed lobar atrophy（i. e., Pick's disease）, comprises Pick body disease（PBD）and lobar atrophy with ubiquitinated inclusions（LA with UI）. In Japan, PBD and LA with UI have an equal incidence. The degeneration pattern of cerebrum and of subcortical nuclei in PBD is similar to that of LA with UI. Brain degeneration eventually becomes very severe in both diseases. Pick's disease usually exhibits significant variation in the degree/distribution of brain atrophy. About a half of the cases show hemispheric predominance in atrophy. Cases with left hemisphere-predominant atrophy are approximately twice as many as those with right hemisphere-predominant atrophy. Variation is also noted in the lobar atrophy. In Japan, the incidence of cases with temporal lobe-predominant atrophy is about twofold higher than that of cases with frontal lobe-predominant atrophy, which is different from Caucasian cases. Such variations in cerebral atrophy provide a neuropathological basis for three clinical subtypes of fronto-temporal lobe degeneration（FTLD）. Anterior type dementia showing diffuse cortical atrophy includes dementia with motor neuron disease, corticobasal degeneration, basophilic inclusion body disease, progressive subcortical gliosis and the frontal lobe degeneration type of frontotemporal dementia. In contrast to Pick's disease, these diseases do not show lobar atrophy and the degree of atrophy remains mild except for basophilic inclusion body disease.