A delay in motor development is often accompanied by a delay in cognitive development, in which case both are parts of a developmental lag or immaturity of the entire cerebrum. The most severe forms of delayed motor development, those associated with spasticity and athetosis, are usually manifestations of prenatal and perinatal diseases of the brain subsumed under the term cerebral palsy; these are discussed in Chap. 37.
In assessing developmental abnormalities of the motor system in the neonate and young infant, the following maneuvers, which elicit certain postures and reflexive movements, are particularly useful: 1.
The Moro response is the infant’s reaction to startle and can be evoked by suddenly withdrawing support of the head and allowing the neck to extend. A loud noise, slapping the bed, or jerking one leg will have the same effect, causing an elevation and abduction of the arms followed by a clasping movement to the midline. This response is present in newborns and infants, it wanes after 2 months and is no longer elicitable after about 5 months of age, and its absence before that time or persistence afterward indicates a disorder of the motor system. An absent or inadequate Moro response on one side is found in infants with hemiplegia, brachial plexus palsy, or a fractured clavicle. Persistence of the Moro response beyond 4 or 5 months of age is noted only in infants with severe neurologic defects.
2.
The tonic neck reflex consisting of extension of the arm and leg on the side to which the head is passively turned and flexion of the opposite limbs, if obligatory and sustained, is a sign at any age of pyramidal or extrapyramidal motor abnormality. Barlow reports that he has obtained this reflex in 25 percent of developmentally delayed infants at 9 to 10 months of age. Fragments of the reflex, such as a brief extension of one arm, may be elicited in 60 percent of normal infants at 1 to 2 months of age and may be adopted spontaneously by the infant up to 6 months of age. As with the Moro response, persistence beyond this age represents a malfunction of the nervous system.
3.
The placing reaction in which the foot or hand, brought into contact with the edge of a table, is lifted automatically and placed on the flat surface, is present in all normal newborns. Its absence or asymmetry in infants younger than 6 months of age indicates a motor abnormality.
4.
In the Landau maneuver, the infant, if suspended horizontally in the prone position, will extend the neck and trunk and will break the trunk extension when the neck is passively flexed. This reaction is present by age 6 months; its delayed appearance in a hypotonic child is indicative of a faulty motor apparatus.
5.
If an infant is held prone in the horizontal position and is then dropped toward the bed, an extension of the arms is evoked, as if to break the fall. This is known as the parachute response and is elicitable in most 9-month-old infants. If it is asymmetrical, it indicates a unilateral motor abnormality.
The detection of gross delays or abnormalities of motor development in the neonatal or early infantile period of life is aided little by tests of tendon and plantar reflexes. Arm reflexes are always rather difficult to obtain in infants, and a normal neonate may have a few beats of ankle clonus. The plantar response tends to be wavering and uncertain in pattern. However, a consistent extension of the great toe and fanning of the toes on stroking the side of the foot is abnormal at any age.