—筋炎関連自己抗体（4）—封入体筋炎

Sporadic Inclusion Body Myositis

封入体筋炎は，嚥下障害や手指・手関節屈筋群，大腿四頭筋の筋力低下と筋萎縮が緩徐に進行する難治性筋疾患である。診断には侵襲を伴う筋生検が不可欠である。約半数の患者血中に細胞質5'-ヌクレオチダーゼ1A抗体が検出されるが，本抗体の診断的意義については肯定的な意見がある一方，有用性には限界があるとの見解もある。病因的意義を支持する能動免疫の結果が示されているが，今後より詳細な検証が必要である。

Abstract

Inclusion body myositis (IBM) is an idiopathic inflammatory muscle disease that predominantly affects elderly men over the age of 50 years, and the number of patients is rapidly increasing in Japan. Generally, muscle weakness and atrophy occur asymmetrically in the flexor muscles of the fingers and wrists and the quadriceps muscles. Invasive muscle biopsy is essential for the diagnosis of IBM. Although its pathogenesis is not yet understood, both inflammatory as well as degenerative mechanisms are postulated to be involved. In particular, degeneration of the IBM muscle may be associated with the IFN-II secretion by highly differentiated CD8+ T lymphocytes. Cytoplasmic 5'-nucleotidase 1A (cN1A) antibody has been detected in the blood samples of approximately half of the patients with IBM. While there are positive opinions about the diagnostic significance of the antibody, its usefulness for the diagnosis of IBM is limited. The results of passive immunization support its etiologic significance; however, more detailed verification, including active immunization, is needed in the future.