Hypotonia (low muscle tone) is defined as a reduced resistance to passive range of motion. Another definition is an impairment of the ability to sustain postural control and movement against gravity (Peredo, 2009). Importantly, this should be differentiated from weakness, which is a reduction in the maximum power that can be generated. For example, weak infants always have hypotonia, but hypotonia may exist without weakness. Hypotonia is a symptom of neurological dysfunction and/or disease. Management of the baby with hypotonia raises a number of important issues:
- Can you recognise when patient with abnormal tone has a concerning history?
- Do you know how to do a complete tone examination?
- Do you know what other exam must be done?
- When should you refer to a paediatrician?
- When is it appropriate to adjust?
- What other management might you do?
When do you refer to a Chiropractor with extra knowledge in this area? Hopefully every baby you examine will undergo a thorough and complete tone exam. These tests should include:
- The Pull to Sit Test
- Vertical Suspension
- Ventral Suspension
- Passive Muscle Palpation
- Range of Motion
- Scarf/Heel to ear/Popliteal Angle Tests
- Hip Abduction
- Foot Dorsiflexion
Other examinations should include; strength evaluation, key physical examination, and muscle stretch reflexes. Observation is important and you should look for:
- Lack of spontaneous movement
- Unusual postures, such as the frog leg position and/or arms/legs extended
- Pectus excurvatum (present with weakness of chest wall)
- Occipital Plagiocephaly
- If sitting – does the head fall forward, do the shoulders droop or limbs hang limply
- Dislocation of the hips, joint contractures
- Abnormalities in stability and movement (E.g.: Commando crawl, W-sitting)
Once you determine that an infant has low tone you have the important task of trying to identify cause. Firstly, in what part of the nervous system are the issues occurring, and secondly, is the issue one of function or pathology? Disorders of tone can occur anywhere between the brain and the muscle itself. It is essential that you identify whether the patient is in your paradigm of care, i.e.: Do they need referral for medical diagnosis and management.
66-88% of infants that present will have central causes of hypotonia (Harris, 2008). This means that the hypotonia is caused by a known or unknown CNS disorder/dysfunction. The most common central cause of hypotonia in infants is cerebral palsy or hypoxic encephalopathy (Peredo, 2009).
A methodical approach to central causes makes the process less daunting for the Chiropractor. Throughout the history and examination consider the following (Bodensteiner JB, 2008):
- Acute illnesses and systemic diseases (E.g.: Sepsis and congestive heart failure)
- Hypoxic-ischemic encephalopathy, brain insult, intracranial haemorrhage (consider with history of birth trauma/difficulty)
- Syndromic conditions (chromosomal disorders/congenital syndromes, such as Down syndrome, Prader Willi, here you should look for dysmorphic and somatic malformations)
- Structural congenital CNS abnormalities (rarely present with hypotonia alone, look for other CNS signs, such as seizures)
- Inborn errors of metabolism, and neurometabolic diseases (look for multisystem/organ involvement)
- Upper cervical spine pathology such as ligamentous injury or Chiari malformations (Early chiari signs include: poor oropharyngeal dysfunction - aspiration, regurgitation, choking, dysphagia, abnormal vocal cord function, and chronic cough)
- Peripheral causes make up the remainder. The most common neuromuscular causes, are congenital myopathies, congenital myotonic dystrophy and spinal muscular atrophy.
Correction of the subluxation is a Chiropractor’s primary responsibility when it comes to management. The subluxation (when it exists without concurrent pathology) generally has predictable and consistent affects on muscle tone. For example, the upper cervical subluxation typically causes inhibited cervical flexor tone/strength and facilitated extensor tone, thus delays in ability on the pull to sit test. The shoulder, elbow and wrist subluxation will affect ability with prone time. Any subluxation in the cranial, spinal or extremity system can have afferentation affects, and influence central sensory-motor integration and motor output.
There are a number underlying physiological mechanisms by which Chiropractic may influence an infant’s muscle tone. These include; supraspinal influences on muscle tone (Bodensteiner, 2008), sensory-motor integration, thixotrophy, muscle facilitation/inhibition, central sensitization, nocifensive reflexes and antalgia (Knutson GA, 2003).
Again, generally speaking, the subluxation had predictable and consistent indicators in the history and examination and the Chiropractor can identify these patterns. In my experience the most powerful influence on muscle tone is correction of the primary upper cervical subluxation pattern (when it is present), thus the Chiropractor should not shy away from correcting this provided that pathology is excluded, the pattern is clearly identified, and the adjustment is low force and specific.
Secondary management approaches may include looking at sympathetic nervous system influences, addressing any areas of muscle spasm, limbic effects (E.g.: Emotional state of mother/baby); addressing any altered visceral pain (E.g.: “Colic”, reflux, gut issues) and addressing any overuse of certain positions (E.g.: Car seats, carriers). In addition, ensure that motor development is proceeding in the normal manner (primitive reflexes > postural reflexes > cognitive control). Exercises are another useful approach – ensure that the exercises you prescribe are age and developmental level appropriate.
In summary, work in this area is hugely satisfying, with immediate and progressive results. On the flip side, you adopt a level of huge responsibility to the children in front of you.
May you use your educated and innate intelligence to assist every child who presents to you to achieve an optimal start to their life.
Written by Adam Stewart, Chiropractor
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