Hipotoni, eklemlerin pasif hareketlerine karsi kasin gösterdigi dirençte azalma olup, hipotonik infant, süt çocuklarinda degisik nedenlere bagli gelisebilen hipotoniyi tanimlamak için kullanilan genel bir terimdir. Kas tonusu, santral ve periferik sinir sistemleri tarafindan kontrol edilen bir refleks aktivite ile olusturulur. Ancak tendon, eklem ve kaslarin fiziksel özellikleri ve birbirleriyle anatomik iliskileri de tonusu belirgin ölçülerde etkilemektedir. Bu yapilarin degisik nedenlere bagli gelisen bozukluklari hipotoniye yol açarak hipotonik infant basligi altinda heterojen bir grup olustururlar (1-4). Hipotoniye yol açan hastaliklar genel olarak iki ana gruba ayrilir (Tablo1):1) Belirgin kas güçsüzlügünün eslik etmedigi nonparalitik grup (Santral hipotoni) 2) Kas güçsüzlügünün klinik tabloya hakim oldugu paralitik grup (Periferik hipotoni)Ancak bazi multisistemik hastaliklarda hem santral sinir sistemi hem de periferik yapilar tutularak hipotoni gelisebilir (Tablo1).
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