Dissociated motor development--developmental patterns, clinical characteristics, causal factors and outcome, with special reference to late walking children.

Dissociated motor development, defined as marked gross motor delay without any abnormal neurological signs and contrasting to a normal fine motor-adaptive performance, was studied prospectively in a consecutive in a consecutive series of 78 children, 48 girls and 30 boys, aged 7-23 months at first examination. When 17 months of age, 10 of them had become normalized, and in further three a disability explaining their gross motor delay had been diagnosed. At an average age of 4.2 years, the remaining 65 late walkers were, regardless of cause and developmental and neurological findings at final follow-up, characterized by a number of deviating clinical features as muscular hypotonia (71%), shuffling (51%) and dissociated or late pattern of learning to sit (79%). In 30 out of 65 late walkers (46%) a defined clinical condition of probable pathogenetic implication was found. In 35 out of 65 late walkers (54%), no explaining clinical condition was found. They have been designed to be idiopathic late walkers. Except for muscular hypotonia, present in 77%, conventional neurology was normal in this group. Minor neurological signs such as a positive Foerster sign, defect balance reactions in standing, or asymmetry in prewalking locomotion were, however, occasionally and temporarily observed. Girls were overrepresented among idiopathic late walkers, 69% compared to 43% among the symptomatic late walkers. Complete normalization was more common in the idiopathic group (66%) than in the symptomatic group (27%). Early differentiation between the late walkers who were normalized and those who developed mild mental retardation or neurological handicaps was difficult but not quite impossible. Heredity for shuffling, a non-revealing pre- and perinatal history, a developmental pattern of late learning to sit, and shuffling favoured a normal outcome. Creepers with a dissociated pattern of learning to sit and crawlers with muscular hypotonia were found to have an increased risk for later handicap.