Kocher–Debré–Semelaigne syndrome (KDSS) is hypothyroidism in infancy or childhood characterised by lower extremity or generalized muscular hypertrophy (Herculean appearance[1]), myxoedema, short stature, and cognitive impairment.
[11] EMG is either normal or may show myopathic low amplitude and short duration motor unit action potentials (MUAPS).
[13] Yet another speculation is an excess intra cellular calcium due to ineffective reuptake into the sarcoplasmic reticulum, which causes a sustained contraction and thereby hypertrophy.
This may occur as a result of reduction in muscle mitochondrial oxidative capacity and beta-adrenergic receptors, as well as the induction of an insulin-resistant state, due to decrease in thyroid hormones.
[25][26] As both hyper- and hypothyroidism disrupts muscle glycogen metabolism, it is important to keep in mind differential diagnoses and their comorbidities when trying to determine whether signs and symptoms are either primary or secondary disease.