Abnormal Truncal Muscle Tone as a Useful Early Marker for Developmental Delay in Low Birth Weight Infants

¹ From the Divisions of Neonatology, Child Development, and General Pediatrics of The Children's Hospital of Philadelphia, and the Department of Pediatrics of the University of Pennsylvania School of Medicine, Philadelphia, and the Division of Neonatology, Department of Pediatrics, University of Minnesota School of Medicine, Minneapolis

Thirty-four outborn premature infants of appropriate gestational ages with birth weights less than 1,750 g were seen in follow-up at 3, 6, 12, and 18 months, corrected age to assess the incidence of abnormalities of muscle tone and the relationship of the site of early abnormalities to 18-month developmental status. The incidence of abnormal tone was most common at 3 months and declined with increasing age. The percentages of infants with abnormal tone at 3, 6, 12, and 18 months, respectively, were: increased lower extremity tone—62%, 71%, 38%, 9%; decreased lower extremity tone—3%, 3%, 6%, 9%; increased truncal tone—41%, 15%, 6%, 0%; decreased truncal tone—21%, 18%, 15%, 6%. Infants with truncal hypertonicity at 3 months had significantly lower Bayley motor and mental scores at 18 months when compared with infants with normal truncal tone (P < .05). However, infants with lower extremity hypertonicity at 3 months were no different developmentally at 18 months from infants with normal tone. Infants with truncal or lower extremity hypotonicity fared the worst developmentally (P < .05). We conclude that there is a high incidence of abnormal muscle tone in premature infants up to 18 months of age and that early truncal tone abnormalities are associated with a worse developmental outcome.

Key Words: muscle tone abnormality • low birth weight infant • neurologic assessment • developmental delay

Submitted on June 4, 1984
Accepted on July 18, 1985

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