Hypotonia can occur due to dysfunction anywhere along the neuroaxis. Can be acquired or inherited. The MCC of acquired hypotonia is HIE, and the MCC of congenital hypotonia is Down syndrome.
A normal young infant should be able to keep the head in the same position when brought from a supine to a sitting position.
- A normal young infant in horizontal suspension
- Holds head in extension
- Holds back straight, elbows flexed, knees partly flexed
- A normal young infant in vertical suspension
- Be able to be held beneath the arm pits
Causes
- Structural causes
- HIE: associated w/prematurity, asphyxia, limpness, stupor, poor cry, poor DTRs, irritability, f/b increased tone and DTRs; seizures may be present
- Brain malformations
- Syndromic causes
- Down syndrome: Characteristic facies, CHD
- Prader-Willi syndrome: LGA, Hypogonadism
- Marfan’s syndrome: Arachnodactily
- Turner syndrome: Neck webbing, CHD, Renal anomalies
- Dysautonomia: Resp infections, corneal anesthesia
- Degenerative causes
- Tay-sachs disease: chery red macula, ashkenazi jew origin
- Metachromati leukodystrophy
- Systemic disorders and metabolic disease
- Malnutrition
- Hypothyroidism
- Hypercalcemia
- Lowe’s disease
- Pompe’s disease
- Leigh’s disease
- LMN causes
- Spinal muscular atrophy (SMA): week cry, absent DTRs, tongue fascculations, decreased spontaneous movements, delay in gross motor milestones
- Infantile botulism: poor feeding, constipation, weak cry, lethargy, facial weakness, ptosis, decreases sucking, difficulty swallowing, drooling, apnoea, Hx of honey consumption, May also be found in soil dust
- Myasthenia gravis: similar to infantile boutlism
- Myotonic dystrophy type I: failure ot suck, ptosis, facial diplegia, thini ribs, polyhydraminos during pregnancy
- Neonatal congenital myopathy (AR or AD): Respiratory failure
- Congenital muscular dystrophy: Early onset, facial weakness, joint contractures, servere MR, seizures
- Hypomyelinating infantile neuropathy
- Benign congenital hypotonia: Dx of exclusion. Improves w/time