Hypotonia

Low muscle tone is a common finding. Remember the following points

Causes of Hypotonia

In newborns

1. Anterior Horn cell disorders like Hypoxic-ischaemic myelopathy, Spinal muscular atrophy
2. Congenital myelopathy like Charcot Marie Tooth disease
3. Neuromuscular junction disorders like Congenital myasthenia
4. Congenital myopathy like Nemaline myopathy
5. Muscular dystrophy
6. Syndromes- like Downs syndrome, Prader Willi syndrome, Hypothyroidism, Tay Sachs disease, Marfan’s disease

In older children along with the above

• Multiple sclerosis
• Cerebral palsy
• Post meningitis, encephalitis

Examination of Hypotonia

History

Feeding difficulty at birth

Delay in gross development, like delayed walking

Inspection

The attitude of the patient in the bed

• The position of the child tells you about the tone.
• Like frog-like position in infants.
• Look for the degree of abduction at the shoulders and hip. The more hypotonic the child, the more the limb lies on the bed

Classical method

• Standing on the right side of the patient’s bed, ask the child to relax while lying supine.
• You need to assess the passive movements at each joint – the ankle, knee, hip and similarly on the upper limb at the wrist, elbow, shoulder
• Keep your left hand proximal to the joint where the muscle mass is maximum. For example- Keep your hand on the calf muscle when assessing the ankle joint
• Make the whole range of movement and assess the tone. If floppy you may shake the limb to make it obvious.

Palpation

• The muscles may be soft and flaccid to touch

Hypotonia in Infancy approach

A hypotonic infant can be a typical case in neurology station. 

The following points are mandatory 

Points to remember in Prenatal History: 

• History of TORCH infections
• History of antenatal Drugs or alcohol
• Any Maternal illness
• Fetal movements- normal or hypoactive? 

Points in Neonatal History: 

• Complications during Delivery- Prolonged delivery, Blood loss
• Gestation at delivery- Term or preterm or post-term
• Seizures history- Age of presentation, Type of seizures, medications
• Initial presentation of hypotonia- Symptoms and signs

Past Medical History: 

• History of presenting symptoms
• Associated symptoms
• Symptoms of the systemic disease
• The rate of symptom progression
• Developmental History
• Delayed milestone attainment
• Loss of milestones
• Motor, social and language incongruence
• Feeding History

Choking or aspiration

Constipation

Family History: 

• Other members affected
• Sudden deaths in the family
• Consanguinity
• Developmental delay
• Neurological disease 
• Metabolic or genetic diseases 

General Physical Examination: 

1. Obvious deformities
2. Dysmorphism?
3. Head and neck: Microcephaly/ Hydrocephalus
4. Nutritional wasting? 
5. Systems: Cardiovascular findings
6. Liver enlargement
7. Splenomegaly
8. Skeletal and spine abnormalities

Neurological Examination: 

• Muscles: Atrophy/ Hypertrophy
• Cranial nerve observation
  • Ptosis
  • Facial expression 
  • Extraocular movements
  • Muscles of facial expression
  • Fasciculations of tongue
• Tone: Hypotonic/ Hypertonic
• Posture
• Horizontal and vertical suspension
• Scissoring or spasticity
• Power
• Reduced/ Normal
• Proximal versus distal 
• Reflexes: Hypotonia/ Hyperactive/ Clonus

The following questions can be asked following the presentation.

Investigations: 

1. Thyroid functions- TSH, free T4, 
2. Electrolytes (including calcium) 
3. Imaging- CT/MRI head
4. EEG
5. Karyotype
6. Metabolic Disease Suspected: 
   1. Urine and serum amino acids
   2. Urine organic acids
   3. Blood gas
   4. Serum ammonia
7. Liver function tests 
8. Creatine kinase