パピオン犬およびパピオン関連犬種における神経軸索ジストロフィーと小脳皮質アビオトロフィーの臨床・病理所見(病理学)

摘要

パピヨン2例および関連雑種1例の神経軸索ジストロフィー(NAD)を検索した.さらに,パピヨン小脳皮質アビオトロフィー(CCA)の1例についても同様に検索した.NADおよびCCAに共通した臨床症状として,若齢時に発症する後肢の運動失調と小脳性運動失調が認められた.これらの臨床症状は急速に進行した.検索例中3例は安楽殺され,他の1例は誤嚥性肺炎により死亡した.MRI検査および剖検ではNADおよびCCAともに中程度から重度の小脳萎縮が観察された.組織学的検索では脊髄背角,延髄楔状核,薄束核,オリーブ核およびその周囲に重度の病変が認められ,多数のスフェロイド形成を伴う軸索変性が特徴的であった.スフェロイドは大型好酸性または顆粒状物として観察され,一部で小膠細胞あるいはMφの反応を伴っていた.これに対してCCAではスフェロイドは殆ど観察されなかった.NADでは軽度から中程度の小脳プルキンエ細胞および課粒細胞の脱落がみられ,これに対してCCAでは本病変がより重度に認められた.以上の検索結果より,NADとCCAは臨床症状およびMRI所見は類似するが,病理組織学的所見が異なり,このことより両疾患の病理発生や原因が異なることが示唆された.NADおよびCCAは常染色体劣性遺伝疾患と推測されていることから,これらの犬種の繁殖には注意が必要と思われる.Neuroaxonal dystrophy (NAD) was examined in two Papillon dogs and a mix breed dog between Papillon and Chihuahua. In addition, cerebellar cortical abiotrophy (CCA) in a Papillon dog, which had similar clinical and magnetic resonance imaging (MRI) features to those of NAD, was also investigated. The common clinical symptoms of all dogs affected with NAD and CCA, were pelvic limb ataxia and cerebellar ataxia including intention tremor, head tremor, and hypermetria in the early onset. These clinical signs were progressed rapidly, and two dogs with NAD were euthanized by owner's request and the other two were died by aspiration pneumonia. MRI examinations and gross observations at necropsy revealed moderate to severe cerebellar atrophy in all cases of NAD and CCA. The most typical histological change of NAD was severe axonal degeneration with marked spheroid-formation in the dorsal horn of the spinal cords, the nuclei gracilis, cuneatus, olivalis and its circumference in the medulla oblongata. The spheroids were characterized as large eosinophilic or granular globes within the enlarged myelin sheaths, sometimes accompanied by moderate accumulation of microglias and/or macrophages. In contrast, such spheroid formation was minimal in the brain of CCA. In the cerebellum, mild to moderate loss of the Purkinje and granular cells were recognized in three dogs with NAD, whereas these changes were more prominent in a dog with CCA. Although the clinical signs and MRI findings relatively resembled between NAD and CCA, the histopathological features considered to be quite differ, suggesting distinct pathogenesis and etiology. Since both NAD and CCA are proposed as the autosomal recessive hereditary disorders, careful considerations might be needed for the breeding of Papillon and Chihuahua dogs.