Hypotonia, or abnormally low muscle tone, is by itself not a disorder but a symptom of an enormous array of issues—many of which can be difficult to diagnose accurately. Even in the absence of a specific underlying diagnosis, however, children with hypotonia can benefit from clinical intervention.
Overview of Hypotonia
The term muscle tone (residual muscle tension or tonus) is the continuous and passive partial contraction of the muscles, or the muscle’s resistance to passive stretch during resting state. Not to be confused with common thought of the term such as muscle mass.
Normally, even when relaxed, muscles have a very small amount of contraction that gives them a springy feel and provides some resistance to passive movement. It is not the same as muscle weakness, although the two conditions can co-exist. Muscle tone is regulated by signals that travel from the brain to the nerves and tell the muscles to contract. Hypotonia can happen from damage to the brain, spinal cord, nerves, or muscles.
Hypotonia can result from damage to the brain, spinal cord, nerves, or muscles, or may be a result of genetic, muscular, or central nervous system (CNS) disorders. The condition appears independently from muscle weakness, although the two may coexist in some disorders, such as motor neuron disease or multiple sclerosis.
Central Hypotonia results from defects at the brain or spinal cord as is the case in MS.
Peripheral Hypotonia that may affect any place between the spinal cord and muscle such as a neuromuscular junction at the connection between the nerve endings and the muscles affected. Nerves bring in the impulse from the central nervous system that makes the muscle maintain contraction or a resting muscle tone.
Defects may also reside at the level of the muscles or all of the above.
Symptoms Of Hypotonia
The most common symptoms of hypotonia are problems with mobility and posture, breathing and speech difficulties, lethargy, laxity in ligaments and joints and poor reflexes. The other symptoms may include: drooling, decreased strength, decreased activity tolerance, rounded shoulder posture, poor attention and motivation. Patients with hypotonia will usually lean onto supports.
Hypotonia can result in falling, abnormal muscular control, general fatigue, muscular weakness, musculoskeletal stiffness.
Hypotonia can also result in deformity.
Causes Of Hypotonia
Hypotonia may sometimes be caused by trauma, genetic heritage, muscle or central nervous system disorders such as multiple sclerosis. However, for many cases the exact cause remains unknown.
Certain health conditions may also be responsible for hypotonia such as:
multiple sclerosis, down syndrome, cerebral palsy, infant botulism, cerebellar ataxia, myasthenia gravis, Prader-Will syndrome, Myotonic dystrophy, Kernicterus, Riley-Day syndrome, Riley-Day syndrome, Hypervitaminosis D, Aicardi syndrome, Canavan disease, Krabbe disease, Achondroplasia, Trisomy 13, Sepsis, Congenital hypothyroidism, Mankes syndrome, Rickets and Spinal muscular atrophy type 1.
Treatment of Hypotonia
Unfortunately, there is no known treatment for hypotonia. The outcome of this condition generally depends on the underlying cause. Hypotonia caused by cerebral dysfunction or motor neuron diseases is usually progressive and can be life threatening. In other cases, patients develop their own coping mechanism to overcome disability to some extent.
If the underlying cause is known, doctors will develop the most appropriate treatment depending on the condition.
Physical therapy can improve motor control and overall body strength. Occupational therapy can help relearn ways to address activities of daily living. Speech-language therapy can help breathing, speech, and swallowing difficulties.
A multidisciplinary approach to supportive and palliative treatment is sometimes needed.
The focus should be on the quality of life:
- Physical or occupational therapy.
- Splints and braces may be needed for limbs.
- Physiotherapy and special seats and wheelchairs can help to minimise joint contractures and scoliosis. Physiotherapy can also allow respiratory exercises.
- Respiratory support may be needed as the respiratory muscles become involved.
- Gastrostomy feeding may be needed as swallowing becomes affected.
The US National Institute of Neurological Disorders and Stroke states that physical therapy can improve motor control and overall body strength in individuals with hypotonia. This is crucial to maintaining both static and dynamic postural stability, which is important since postural instability is a common problem in people with hypotonia. A physiotherapist can develop patient specific training programs to optimize postural control, in order to increase balance and safety. To protect against postural asymmetries the use of supportive and protective devices may be necessary.
Physical therapists might use neuromuscular/sensory stimulation techniques such as quick stretch, resistance, joint approximation, and tapping to increase tone by facilitating or enhancing muscle contraction in patients with hypotonia. For patients who demonstrate muscle weakness in addition to hypotonia strengthening exercises that do not overload the muscles are indicated.
Electrical Muscle Stimulation, also known as Neuromuscular Electrical Stimulation (NMES) can also be used to “activate hypotonic muscles, improve strength, and generate movement in paralyzed limbs while preventing disuse atrophy”. When using NMES it is important to have the patient focus on attempting to contract the muscle(s) being stimulated. Without such concentration on movement attempts, carryover to volitional movement is not feasible. NMES should ideally be combined with functional training activities to improve outcomes.
Some of the newer NMES devices stimulate muscles while also moving limbs such as simulating peddling a bicycle. A motor in the device drives the pedals while electrical stimulation controlled by a computer sends signals to muscles causing them to contract and relax.
Occupational therapy can assist the patient with increasing independence with daily tasks through improvement of motor skills, strength, and functional endurance. Speech-language therapy can help with any breathing, speech, and/or swallowing difficulties the patient may be having. Therapy for infants and young children may also include sensory stimulation programs.” A physical therapist may recommend an ankle/foot orthosis to help the patient compensate for weak lower leg muscles. Toddlers and children with speech difficulties may benefit greatly by using sign language.