Hypotonia: Definition, Symptoms & Causes

Instructor: Artem Cheprasov

Artem has a doctor of veterinary medicine degree.

We take something called muscle tone for granted, as we rarely think about it. But a condition called hypotonia can reveal the true importance of muscle tone. Find out more in this lesson.

What is Hypotonia?

Tone. It has nothing to do with music. It has nothing to do with how fit you look. Well, at least not with respect to this lesson. Tone, tonicity, or tonus are all words that describe the normal or neutral state of tension of bodily tissues that keep everything in shape and ready to function when called upon.

Usually, this term specifically refers to the modest continuous contraction of a muscle or group of muscles that hold a structure in position for a long period of time without fatigue. For example, it's muscle tone that helps you keep your back and neck straight, eyes open, and jaw shut for prolonged periods of time without you even thinking about it (especially when you're awake).

So, what is hypotonia then? You can spot the 'tone' in hypotonia. 'Hypo-' means abnormally low or diminished. So, hypotonia refers to diminished muscle tone.

Causes of Hypotonia

Hypotonia is not a disease; it is a sign of a problem. But there could be many problems that cause hypotonia. Some disorders associated with hypotonia include:

  • Amyotrophic lateral sclerosis (ALS), more commonly called Lou Gehrig's disease. This is a degenerative neuromuscular disorder.
  • Muscular dystrophies, which are a group of over 30 disorders that share an important commonality. These disorders are characterized by the degeneration and progressive weakness of skeletal muscles. Skeletal muscles are the muscles that are under voluntary control and help you move your body.
  • Cerebral palsy, a term for one of various disorders that are characterized by improper movements and posture.
  • Infections of the brain or associated structures, as per meningitis and encephalitis.
  • Myasthenia gravis, a condition that results in muscle weakness.
  • Toxins, such as those produced by Clostridium botulinum, a bacterium responsible for botulism.
  • An injury to the spinal cord.
  • Down syndrome
  • Brain damage during birth, such as due to a lack of oxygen.

There are many other disorders that can cause hypotonia, some of which are very rare or not as noticeable. This includes some cases of osteomalacia (the adult version of rickets), aromatic amino acid decarboxylase deficiency, tyrosine hydroxylase deficiency, and Leigh syndrome, to name just a few.

Signs and Symptoms

The signs of hypotonia can be different depending on which muscle(s) are affected and what the underlying cause is. Children born with hypotonia may have the following signs:

  • A 'floppy' head because they can't control their neck muscles.
  • A general feeling that the child is limp when you hold them.
  • The inability of the child to hold their knees and elbows bent.
  • Difficulty suckling and even swallowing.
  • A cry that isn't noticeable, as in most children.
  • The inability to grasp objects, such as a pencil.

Other signs that may be present at any age (including in adults):

  • Decreased strength, which may manifest itself as an inability to lift something.
  • Weak reflexes
  • Difficulty speaking
  • A weak posture. This could mean the person has problems getting up from a chair.
  • An abnormally high amount of flexibility in joints, like with the knees, hips, and elbows.
  • Decreased endurance

Lesson Summary

Hypotonia refers to diminished muscle tone. Muscle tone, tonicity, or tonus is usually used to describe the modest continuous contraction of a muscle or group of muscles that hold a structure in position for a long period of time without fatigue.

Hypotonia is not a disease, but it can be caused by a very long list of problems, including:

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