hypotone

Hypotone is a term used in medicine to describe decreased muscle tone, a condition more commonly referred to as hypotonia. The noun hypotone is less common in modern clinical usage, with hypotonia and related descriptions being preferred. In clinical settings, hypotone describes reduced resistance to passive limb movement, often giving a floppy or low-tone appearance. Individuals with hypotone may have normal or near-normal muscle strength, but their limbs feel lighter and may be slower to move. Reflexes can be diminished, though findings vary with age and underlying cause. Hypotone is a sign rather than a disease, and it can range from mild to severe.

Causes of hypotone are diverse and can be congenital or acquired. Central or supraspinal causes include brain malformations, perinatal asphyxia, trauma, infections, or neurodevelopmental disorders that affect motor pathways. Peripheral causes involve motor neuron disease, muscular dystrophies, spasticity syndromes with fluctuating tone, and neuromuscular junction disorders. Metabolic or endocrine conditions, such as thyroid hormone abnormalities, can contribute. In many cases, hypotone arises from a combination of factors, and in infants it may be part of a broader developmental syndrome.

Diagnosis involves a comprehensive clinical assessment complemented by history, growth and development monitoring, and targeted tests. Neurological examination helps classify the hypotonia as central or peripheral. Additional investigations may include metabolic panels, genetic testing, imaging studies, and electrophysiological testing to identify underlying etiologies.

Management focuses on addressing the root cause when possible and on supportive measures. Early physical and occupational therapy aim to improve movement, strength, and motor control. Family education, regular follow-up, and multidisciplinary care are often required. Prognosis varies widely depending on cause, with some children improving over time and others experiencing persistent hypotonia.

See also hypotonia, muscle tone, neurology.