Differential Diagnosis of Neonatal Hypotonia

Initial Clinical Localization

The American Academy of Pediatrics recommends that preserved or increased deep tendon reflexes with abnormal plantar responses distinguish central from peripheral causes 1
Normal or only mildly elevated creatine kinase (CK) levels are associated with central hypotonia 1
Diminished or absent deep tendon reflexes are the hallmark of peripheral involvement 1
Tongue fasciculations strongly suggest spinal muscular atrophy and require urgent referral 2
Significantly elevated CK (>3× normal) indicates muscular dystrophy and mandates immediate neurology referral 2
Preserved feeding and bulbar function suggest congenital myopathy over more severe neuromuscular disorders 1

Hypothyroidism is a treatable cause of central hypotonia and must not be missed 2
Prader-Willi syndrome should be considered in any infant with significant hypotonia, poor feeding, reduced spontaneous arousal, and hypogonadism (undescended testes, small phallus, or small clitoris) 3, 4
For newborns with hypotonia, congenital hypothyroidism, and hypotonia, genetic testing for NKX2.1 (thyroid transcription factor) mutations or deletions is recommended 5
Diazepam exposure causes hypotonia, poor suck, hypothermia, and apnea with onset from hours to weeks 6, 7

Elevated creatine kinase level (>3× normal) indicates muscular dystrophy 2
Thyroid function tests can diagnose hypothyroidism, a treatable cause of central hypotonia 2
Maternal drug history can identify drug withdrawal syndromes 6, 7
MRI brain/spine should be performed in all cases, as it is abnormal in 56% and diagnostic in 33% is not cited, however, Use lowest radiation dose CT only when MRI unavailable 5

Refer immediately to early intervention programs for needs assessment, even without definitive diagnosis 2
Initiate physical therapy focusing on antigravity muscle power and gross motor skills 2
Begin occupational therapy for sensory integration and fine motor skills 2
Perform speech/language evaluation including oral-motor functioning assessment 2
CK >3× normal: Immediate pediatric neurology referral for suspected muscular dystrophy 2
Fasciculations: Urgent referral for suspected spinal muscular atrophy due to rapid deterioration risk 2
Monitor respiratory function closely, as respiratory failure can occur during acute illness in neuromuscular disorders 2
Regular growth measurements using CDC/WHO curves to detect microcephaly, macrocephaly, or growth impairments 2
Cardiac evaluation for certain congenital myopathies that develop cardiomyopathy 1

Do not delay early intervention services while awaiting definitive diagnosis—therapy must begin immediately 2
Do not diagnose hypotonic cerebral palsy without excluding other causes, especially with uneventful perinatal history and normal brain imaging 2
Do not miss treatable conditions: Pompe disease (enzyme therapy), hypothyroidism (hormone replacement), and spinal muscular atrophy (emerging therapies) 2
Do not overlook respiratory monitoring in neuromuscular disorders 2