Muscular pseudohypertrophy-hypothyroidism syndrome

Muscular pseudohypertrophy-hypothyroidism syndrome, also known as Kocher-Debré-Sémélaigne syndrome, is a rare condition characterized by the combination of congenital or acquired hypothyroidism with generalized muscular pseudohypertrophy (enlarged muscles that appear well-developed but are actually weak). This syndrome predominantly affects children and is caused by longstanding, untreated or inadequately treated hypothyroidism. The muscular enlargement gives the child a 'Herculean' or athletic appearance despite significant muscle weakness and stiffness. The condition primarily affects the skeletal muscular system and the endocrine system. Key clinical features include diffuse enlargement of muscles (particularly in the calves, thighs, and arms), muscle stiffness, slowness of movement, muscle weakness, and the classic signs of hypothyroidism such as growth retardation, delayed bone age, fatigue, constipation, dry skin, and intellectual slowing. The muscles may feel firm and rubbery on palpation. Laboratory findings typically reveal elevated thyroid-stimulating hormone (TSH), low thyroid hormone levels (T3 and T4), and often markedly elevated creatine kinase levels reflecting muscle involvement. The condition is generally reversible with appropriate thyroid hormone replacement therapy. Treatment with levothyroxine leads to gradual resolution of the muscular pseudohypertrophy and improvement in muscle strength, along with correction of the hypothyroid state. Early diagnosis and treatment are important to prevent long-term complications including growth failure and neurodevelopmental delay. The prognosis is excellent when thyroid replacement therapy is initiated promptly.

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