Myositis - Kinen

Myositis is a condition in which muscles are infected with bacteria, viruses, parasites, etc., causing muscle weakness, muscle pain, and muscle atrophy. However, it is often used synonymously with polymyositis or dermatomyositis, which is a condition in which the cause is unknown and causes muscle weakness and atrophy of the limbs along with inflammatory cell infiltration. Polymyositis and dermatomyositis are specific diseases (incurable diseases) of unknown cause, and are considered to be autoimmune diseases or collagen diseases. The main symptoms are muscle weakness and atrophy of the facial muscles, neck muscles, and limbs, and among the limbs, the shoulders and lower back muscles, which are close to the trunk, are particularly affected. Dermatomyositis is a condition that is accompanied by skin rash, skin atrophy, and dilated capillaries. Along with muscle weakness, fever, joint swelling, and muscle pain are often present, and inflammatory signs such as increased erythrocyte sedimentation rate are also seen. Both men and women can develop this condition, but it is more common in women. Corticosteroids are often highly effective.

[Eijiro Satoyoshi]

Source: Shogakukan Encyclopedia Nipponica About Encyclopedia Nipponica Information | Legend

筋が細菌やウイルス、寄生虫などに感染して筋力低下、筋痛、筋萎縮(いしゅく)などを示すものを一般的に筋炎とよんでいるが、原因不明で筋に炎症性細胞浸潤とともに四肢筋の筋力低下や筋萎縮を示してくる多発性筋炎ないし皮膚筋炎と同義語に用いられることが多い。多発性筋炎・皮膚筋炎は原因不明の特定疾患（難病）の一つで、自己免疫疾患ないし膠原(こうげん)病の一つとされている。顔面筋、頸筋(けいきん)および四肢の筋の筋力低下と筋萎縮を主とするもので、四肢のうちでも躯幹(くかん)に近い肩や腰の筋が強く冒される。皮膚の発疹(はっしん)、皮膚の萎縮や毛細血管の拡張を伴うものを皮膚筋炎とよんでいる。筋力低下とともに発熱、関節腫脹(しゅちょう)、筋痛を示すことが多く、血沈促進などの炎症所見がみられる。男女ともに発症するが、女性が多い。副腎(ふくじん)皮質ステロイド剤が著効を示すことが多い。

［里吉営二郎］

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