Hypotoni

Hypotoni, or hypotonia, is a clinical finding defined by decreased resistance to passive movement in the muscles, producing a floppy or diminished ability to support posture. In infants, hypotonia can present with poor head control, lax joints, and delayed motor development. It may be a normal variant in newborns or indicate an underlying disorder affecting the brain, spinal cord, nerves, muscles, or neuromuscular junction.

Causes are broad and commonly categorized as central (neural control from brain or spinal cord) or peripheral (nerve, neuromuscular junction, or muscle). Central hypotonia is often associated with brain injuries, cerebral palsy, genetic syndromes, or metabolic disorders. Peripheral hypotonia includes spinal muscular atrophy, muscular dystrophies, congenital myopathies, neuropathies, and myasthenic disorders. Some conditions present with mixed features or transient physiologic hypotonia in newborns.

Evaluation starts with a detailed history and neurologic examination, focusing on developmental milestones, feeding, reflexes, and tone patterns. Basic laboratory tests such as thyroid function and metabolic screening may be used. Neuroimaging (MRI) and electrophysiologic studies (EMG, nerve conduction) help distinguish central from peripheral causes. Genetic testing may identify syndromic or specific diagnoses.

Management targets the underlying cause when possible and emphasizes supportive therapies, including physical and occupational therapy, activity modification, and nutritional support. Prognosis varies widely, from transient, self-limiting hypotonia to complex, lifelong motor impairment depending on the underlying condition.