Hypotonia means decreased muscle tone.

Hypotonia is often a sign of a worrisome problem. The condition can affect children or adults.

Infants with hypotonia seem floppy and feel like a "rag doll" when held. They rest with their elbows and knees loosely extended, while infants with normal tone tend to have flexed elbows and knees. They may have poor or no head control. The head may fall to the side, backward, or forward.

Infants with normal tone can be lifted with the parent's hands placed under the armpits. Hypotonic infants tend to slip between the hands as the infant's arms rise without resistance.

Muscle tone and movement involve the brain, spinal cord, nerves, and muscles. Hypotonia may be a sign of a problem anywhere along the pathway that controls muscle movement.

Causes may include:

• Brain damage or encephalopathy, due to:
  • Lack of oxygen before or right after birth
  • Problems with brain formation
• Disorders of the muscles, such as muscular dystrophy
• Disorders that affect the nerves that supply muscles (called motor neuron disorders)
• Disorders that affect the ability of nerves to send messages to the muscles:
  • Infant botulism
  • Myasthenia gravis
• Inborn errors of metabolism (rare genetic disorders in which the body cannot properly turn food into energy)
• Infections
• Other genetic or chromosomal disorders or defects that cause brain and nerve damage, such as:
  • Down syndrome
  • Prader-Willi syndrome
  • Tay-Sachs disease
  • Trisomy 13
• Other miscellaneous disorders:
  • Achondroplasia
  • Congenital hypothyroidism
  • Congenital cerebellar ataxia
  • Marfan syndrome
  • Poisons or toxins
  • Spinal cord injuries that occur around birth