Hypotonia

Central hypotonia accounts for 60 to 80% of all hypotonia in infants.[4] Hypotonic patients may display a variety of objective manifestations that indicate decreased muscle tone. Motor skills delay is often observed, along with hypermobile or hyperflexible joints, drooling and speech difficulties, poor reflexes, decreased strength, decreased activity tolerance, rounded shoulder posture, with leaning onto supports, and poor attention. The extent and occurrence of specific objective manifestations depends upon the age of the patient, the severity of the hypotonia, the specific muscles affected, and sometimes the underlying cause. For instance, some people with hypotonia may experience constipation, while others have no bowel problems.

The most common cause of central hypotonia in newborns is hypoxic ischemic encephalopathy. Brain malformations and inborn errors of metabolism account for 13% and 3% respectively.[4] Causes that affects the central nervous systems are: chromosomal disorders, inborn errors of metabolism, cerebral dysgenesis, and trauma to the brain and spinal cord.[5] Metabolic causes includes: glycogen storage disease type II, pyruvate dehydrogenase deficiency, mitochondrial disease, Zellweger syndrome, Smith–Lemli–Opitz syndrome, and congenital disorder of glycosylation. Metabolic disorders in infants are usually presented with various other features such as dysmorphic feature, seizures, encephalopathy, biochemistry profile apart from hypotonia.[5]

Some conditions known to cause hypotonia include:

Congenital – i.e. disease a person is born with (including genetic disorders presenting within 6 months)

• Genetic disorders are the most common cause
  • 22q13 deletion syndrome a.k.a. Phelan–McDermid syndrome
  • 3-Methylcrotonyl-CoA carboxylase deficiency[6]
  • Achondroplasia
  • ADNP syndrome
  • Aicardi syndrome
  • Autism spectrum disorders[7]
  • Canavan disease
  • Centronuclear myopathy (including myotubular myopathy)
  • Central core disease
  • CHARGE syndrome
  • Cohen syndrome
  • Costello syndrome
  • Dejerine–Sottas disease (HMSN Type III)
  • Down syndrome a.k.a. trisomy 21 — most common
  • Ehlers–Danlos syndrome
  • Familial dysautonomia (Riley–Day syndrome)
  • FG syndrome
  • Fragile X syndrome
  • GLUT1 deficiency syndrome
  • Griscelli syndrome Type 1 (Elejalde syndrome)
  • Holocarboxylase synthetase deficiency / Multiple carboxylase deficiency[8]
  • Krabbe disease
  • Leigh's disease
  • Lesch–Nyhan syndrome[9]
  • Marfan's syndrome
  • Menkes syndrome
  • Methylmalonic acidemia
  • Myotonic dystrophy
  • Niemann–Pick disease
  • Nonketotic hyperglycinemia (NKH) or Glycine encephalopathy (GCE)
  • Noonan syndrome
  • Neurofibromatosis
  • Patau syndrome a.k.a. trisomy 13
  • Pituitary dwarfism/growth hormone deficiency(in adults)
  • Prader–Willi syndrome
  • Rett syndrome
  • Septo-optic dysplasia (de Morsier syndrome)
  • Snyder–Robinson syndrome (SRS)
  • Spinal muscular atrophy (SMA)
  • Succinic semialdehyde dehydrogenase deficiency (SSADH)
  • Tay–Sachs disease
  • Werdnig–Hoffmann syndrome – Spinal muscular atrophy with congenital degeneration of anterior horns of spinal cord. Autosomal recessive [10]
  • Wiedemann–Steiner syndrome
  • Williams syndrome
  • Zellweger syndrome a.k.a. cerebrohepatorenal syndrome
• Developmental disability
  • Cerebellar ataxia (congenital)
  • Sensory processing disorder
  • Developmental coordination disorder
  • Hypothyroidism (congenital)
  • Hypotonic cerebral palsy
  • Teratogenesis from in utero exposure to Benzodiazepines

The approach to diagnosing the cause of hypotonia (as with all syndromes in neurology) is first localization. The physician must first determine if the hypotonia is due to muscle, neuromuscular junction, nerve, or central cause. This will narrow the possible causes. If the cause of the hypotonia is found to lie in the brain, then it can be classified as a cerebral palsy. If the cause is localized to the muscles, it can be classified as a muscular dystrophy. If the cause is thought to be in the nerves, it is called hypotonia due to polyneuropathy. Many cases cannot be definitively diagnosed.[13]

Diagnosing a patient includes obtaining family medical history and a physical examination, and may include such additional tests as computerized tomography (CT) scans, magnetic resonance imaging (MRI) scans, electroencephalogram (EEG), blood tests, genetic testing (such as chromosome karyotyping and tests for specific gene abnormalities), spinal taps, electromyography muscle tests, or muscle and nerve biopsy.

Mild or benign hypotonia is often diagnosed by physical and occupational therapists through a series of exercises designed to assess developmental progress, or observation of physical interactions. Since a hypotonic child has difficulty deciphering their spatial location, they may have some recognizable coping mechanisms, such as locking the knees while attempting to walk. A common sign of low-tone infants is a tendency to observe the physical activity of those around them for a long time before attempting to imitate, due to frustration over early failures. Developmental delay can indicate hypotonia.

MRI Brain is used to rule out structural malformations in the brain or metabolic disorders.[4] Magnetic resonance spectroscopic imaging is used to detect metabolic disorders.[4]

The outcome in any particular case of hypotonia depends largely on the nature of the underlying disease. In some cases, the underlying cause is treatable. But in general, treatment comprises providing supportive care with rehabilitation services, nutritional and respiratory support.[14]

Along with normal pediatric care, specialists who may be involved in the care of a child with hypotonia include developmental pediatricians (specialize in child development), neurologists, neonatologists (specialize in the care of newborns), geneticists, occupational therapists, physical therapists, speech therapists, orthopedists, pathologists (conduct and interpret biochemical tests and tissue analysis), and specialized nursing care.

If the underlying cause is known, treatment is tailored to the specific disease, followed by symptomatic and supportive therapy for the hypotonia. In very severe cases, treatment may be primarily supportive, such as mechanical assistance with basic life functions like breathing and feeding, physical therapy to prevent muscle atrophy and maintain joint mobility, and measures to try to prevent opportunistic infections such as pneumonia. Treatments to improve neurological status might involve such things as medication for a seizure disorder, medicines or supplements to stabilize a metabolic disorder, or surgery to help relieve the pressure from hydrocephalus (increased fluid in the brain).

The 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.[3] A physiotherapist can develop patient specific training programs to optimize postural control, in order to increase balance and safety.[3] To protect against postural asymmetries the use of supportive and protective devices may be necessary.[3] 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.[3] For patients who demonstrate muscle weakness in addition to hypotonia strengthening exercises that do not overload the muscles are indicated.[3] 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".[3] 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.[3] NMES should ideally be combined with functional training activities to improve outcomes.

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.

The term hypotonia comes from the Ancient Greek ὑπο-, hypo-, 'under' and τόνος, tónos, from τείνω, teinō, 'to stretch'. Other terms for the condition include:

• Hypertonia

• Martin K, Inman J, Kirschner A, Deming K, Gumbel R, Voelker L (2005). "Characteristics of hypotonia in children: a consensus opinion of pediatric occupational and physical therapists". Pediatric Physical Therapy. 17 (4): 275–82. doi:10.1097/01.pep.0000186506.48500.7c. PMID 16357683. S2CID 24077081.

• hypotonia at NINDS
• Hypotonia – Medline Plus