[Neurological prognosis of floppy infants after health examinations].

Objective: The term benign congenital hypotonia is retrospective and refers to infants who are hypotonic at birth or shortly thereafter but later show a normal tone. It encompasses many different pathological processes that affect the brain, motor unit, or both. The majority of affected children have cerebral hypotonia. An increased incidence of mental retardation, learning disabilities, and other sequelae of cerebral abnormality are evident later in life, despite the recovery of a normal muscle tone. We followed floppy infants who were pointed out as showing motor delay on health examinations at 4 or 9 months of age until at least 2 years of age.

Methods: We selected 32 floppy infants (15 males and 17 females) born uneventfully, with no family history, major anomalies, or abnormal findings on brain imaging, and no chromosomal study (G-banding and fluorescence in situ hybridization), serum creatine kinase level, blood lactate and pyruvate level, or blood amino acid abnormalities.

Results: All 32 infants achieved head control, but 2 failed to learn to sit unsupported. These two were diagnosed based on gene analysis with Rett syndrome and spinal muscular atrophy, respectively. Although 27 among the 32 patients became ambulant, 18 (67%) showed mental retardation and 5 (19%) also had autism spectrum disorder. Five patients who could not walk were suspected to have congenital myopathy or congenital malformation syndrome.

Conclusions: After learning to walk independently and recovery of the normal muscle tone, many floppy infants showing motor delay on health examinations at 4 or 9 months of age developed mental retardation and autism spectrum disorder. Prospective follow-up is necessary for early diagnosis and intervention. For patients showing no motor and mental development, further laboratory studies including appropriate gene analysis are important for a definite diagnosis.