|
Hypotonia in Infants Hypotonia is reduced resistance to passive movement of joints. The deficit causing hypotonia 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 8. Sepsis 9. Congestive Heart failure 10. Hypoglycemia
The differential diagnosis of hypotonia is organized anatomically in to central and peripheral causes. Peripheral hypotonia is further divided into disorders of anterior horn cells, peripheral nerves, neuromuscular junction, and muscle. In general, a good history, physical examination, and neurologic exam will lead to the diagnosis.
Characteristics of central hypotonia (60-80% of cases) History: · Seizures · Delay in attaining normal milestones PE: · Don’t track visually · Fail to imitate facial gestures · Lethargic and less alter · Hyperactive DTRs, clones, persistence of primitive reflexes · Poor head control
Characteristics of Peripheral Hypotonia (15-30% of cases) History: · Normal sleep-wake patterns · Feeding difficulties PE: · Responds appropriately to surroundings · Profound generalized weakness · Absent reflexes
Central Hypotonia Hypoxic encephalopathy (19% of cases) Intracranial hemorrhage Perinatal trauma Infections – meningitis or encephalitis Structural abnormalities Chromosomal and Genetic abnormalities (31%) · Tiresome 21 (Downs Syndrome) o Characteristic features: hypotonia, mental retardation, and congenital heart defects o Dysmorphic features present in neonates: flat facial profile and nasal bridge, short neck with excess uncial folds, single transverse palmer crease, upslanting palpebral fissures
· Fragile X o Genetic defect: expansion of trinucleotide repeat (CGG) on X chromosome o Hypotonia is mild and kids are usually diagnosed after failure to meet developmental milestones o Characteristic features: mental retardation, autistic features, macrocephaly, large ears, increased testicular size in puberty
· Prader-Willi syndrome: o Characteristic features: hypotonia, hypogonadism, mental retardation, short stature, and obesity o Genetic defect: deletion of paternal copy of long arm of chromosome 15q11-13 or maternal uniparental dismay
Peripheral Hypotonia Cervical Cord Trauma · Secondary to difficult delivery, usually breech or cervical presentation · Initially present with hyporeflexia and later develop hyperreflexia and spasticity after days to weeks · Development of neurologic deficits below the cervical area including: respiratory depression, vasomotor instability, bladder dysfunction, decreased rectal tone
Anterior Horn Cell Disorders · Werdig- Hoffman syndrome (Spinal Muscle Atrophy) o degeneration of anterior horn cells o Autosomal recessive o 1/3 present in the neonatal period o Maternal history: decreased fetal movements and breech presentation o Features: hypotonia, weakness, absent reflexes, tongue and muscle fasciculations o Infants are very alert and develop normal intelligence
· Pomp’s Disease o Glycogen storage disease type II: acid maltase deficiency o Glycogen deposits in the anterior horn cells, liver, brain and heart o Associated with cardiomyopathy and hepatosplenomegaly o Diagnosis is made by muscle biopsy showing vacuolar myopathy
· Poliomyelitis o Destruction of anterior horn cells by polio virus o Features: abrupt onset of asymmetric weakness, bulbar involvement and encephalitis may be present o Can recover virus from stool
Neuromuscular junction · Transient myasthenia gravis (MG) o 10% of neonates with mothers who have MG o Mother’s antibodies against acetycholine receptor cross the placenta and effect the newborn o Features: decreased tone, weakness, poor suck, and decreased movements. May be confused with sepsis. o Diagnosis confirmed by temporary reversal of symptoms upon edrophonium or neostigmine challenge o Mean duration of symptoms 18 days, typically resolves in 6 weeks
· Congenital myasthenia gravis (MG) o Presents in early infancy with ptosis and ophthalmoplegia (features uncommon in transient MG) o Severe respiratory symptoms requiring assisted ventilation at birth o Persistent episodes of apnea and weakness
· Infantile botulism o Infant ingests C. botulinum spores that germinate in the GI tract and release an serotoxin that interferes with the release of acetycholine. o Subacute or acute onset of hypotonia o 4-5 day prod Rome of constipation, poor feeding, lethargy prior to development of ptosis, decreased eye movements, weakness and areflexic. o Progressive muscle weakness can lead to respiratory failure requiring ventilatory support. o Usually self limited, lasting 2-6 weeks o Treatment: IV human botulism IG
· Aminoglycosides - interfere with the presynaptic release of acetylcholine
· Hypermagnesemia o Occurring secondary to treatment of eclampsia with magnesium sulfate o Mg2+ inhibits release of acetylcholine o Leads to weakness, hypotonia, and increased risk of respiratory failure
Muscle · Congenital Myopathy o There are many forms of myopathies that present in the neonatal period. o Typical features: hypotonia, hyporeflexic, facial paralysis, high arched palate o Diagnosis: muscle biopsy
· Congenital Myotonic Dystrophy (Steinert disease) o Infants born to mothers with moronic dystrophy o Maternal history: polyhydramnios, prolonged labor, and uterine dystocia o Symptoms at birth: hypotonia, facial weakness, areflexia, and respiratory distress o Characteristic facial features: tenting of upper lip, thin cheeks, wasting of temporalis muscle o Motor function improves after 3rd weeks, if infant survives
Benign Congenital Hypotonia · Diagnosis of exclusion · Hypotonia, but no weakness · The reflexes are normal or hypoactive · There may be a slight delay in motor milestones, otherwise development is normal · IQ usually normal · Complications: joint hypermobility leading to frequent joint dislocations especially the shoulder
References: 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. 2006. 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 6. Peredo D, Hannibal M. The Floppy Infant. Pediatrics in Review September 2009 7. Harris, Susan R. Congenital hypotonia: clinical and developmental assessment. Developemental Medicine & Child Neurology May 2008 8. Zafeiriou, Dimitrios I. et al. Clinical and neurophysiological characteristics of congenital myasthenic syndromes presenting in early infancy. Brain & Development January 2004 |