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.
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