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Hypotonia is present when resistance to passive movement is less than normally expected. The deficit causing hypotonia may originate in the brain, spinal cord, peripheral nerves, neuromuscular junction, and muscle. There are also non-neuromuscular entities that may be associated with hypotonia including;

1. Prematurity
   
2. Hypothyroidism
   
3. Rickets
   
4. Malnutrition
   
5. Kernicterus
   
6. Storage diseases
   
7. Down Syndrome

In general, a good history, physical examination, and neurologic exam will lead to the diagnosis. If the infant is lethargic, not following objects with their eyes, delayed in attaining normal milestones, or has had seizures, the lesion is usually of central origin.

1. Disorders of the brain secondary to anoxia, bleeds, trauma, meningitis or encephalitis, structural abnormalities, chromosomal changes, and hypoglycemia.
   
2. DTRs are increased or normal
   
3. Poor head control
   
4. Diagnosis usually obtained through good history and physical examination.

Cervical Cord Trauma-

1. Secondary to difficult delivery, usually breech
   
2. May initially be hypotonic and hyporeflexic but later become hypertonic and increased DTRs
   
3. Will have deficits below the cervical area including respiratory depression and vasomotor instability

1. Werdig- Hoffman syndrome- degeneration of anterior horn cells. Autosomal recessive and 1/3 present in the neonatal period and maternal history may indicate decreased fetal movements. Infants are very alert and develop normal intelligence. Tongue and muscle fasciculations are present. Movements are decreased and there is hyporeflexia
   
2. Pompe's Disease- Glycogen storage in the anterior horn cells. Associated with cardiomyopathy and hepatosplenomegaly
   
3. Poliomyelitis- Viral infection that destroys anterior horn cells. Have asymmetric weakness. May have bulbar involvement. Can recover virus in stool

1. Transient myasthenia gravis- 10% of neonates with mothers who have myasthenia will get antibodies from the mother that bind to and inhibits acetylcholine receptors. There will be decreased tone, suck, and movements. May be confused with sepsis. Will resolve in 6 weeks.
   
2. Congenital myasthenia gravis- present with poor feeding and decreased activity. May have ophthalmoplegia and ptosis.
   
3. Infantile botulinism- Infant will ingest spores that germinate in the GI tract and release an exotoxin that interferes with the release of acetycholine. Infant usually constipated, poor feeding, weak, ptosis, decreased eye movements, and areflexic. May have respiratory failure and need ventilatory support.
   
4. Aminoglycosides and hypomagnesium may interfere with the release of acetylcholine.

1. There are many forms of myopathies that present in the neonatal period. They are hypotonic and hyporeflexic. Diagnosis is made by muscle biopsy.

1. Development is normal
   
2. There is no evidence of weakness
   
3. The reflexes are normal or hypoactive
   
4. There may be a slight delay in motor milestones
   
5. IQ usually normal
   
6. May be complicated by frequent joint dislocations especially the shoulder
   
7. It is a rule out diagnosis after eliminating other causes of hypotonia.

1. Steifel. Laurence. Hypotonia in Infants Pediatrics in Review. March 1996
2. Arnon S. et al. Human Botulinism Immune Globulin for the Treatment of Infant Botulism. NEJM Feb 2. 20063.
3. NEJM Case: A Newborn Boy with Hypotonia.  NEJM Nov. 16 2006
4. Francisco AM and Arnon S. Clinical Mimics of Infant Botulinism.  Pediatrics April 2007
5. Long S. Infant Botulism and Treatment with BIB-IV.  Pediatric Infectious Disease Journal March 2007
   

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