Neuromuscular System
Examination of neuromuscular function consists of testing reflexes, tone, active motion, strength, and coordination. Limited understanding and cooperation in infants and young children requires adaptation of traditional methods of testing.
After four to five years of age, the standard examination is generally applicable.In infancy, reflex testing includes age-appropriate responses that reflect early immaturity and subsequent maturation of the central nervous system. In newborns and young infants, state of alertness, activity, and comfort influence muscle tone (11—14). If the baby is anxious, upset, restless, or crying, this part of the examination should be postponed. Valid assessment may require several attempts. In the first few months of life, flexor tone predominates. Hypotonia or hypertonicity signals neurologic abnormalities. Increased tone is the symptom of corticospinal or basal ganglion damage. Myopathy, cerebellar dysfunction, and lower motor neuron lesions due to anterior horn disease, neuropathy, or spina bifida all can result in hypotonia. However, a hypotonic stage usually precedes the appearance of increased tone in perinatal anoxic brain damage (l5). This stage of hypotonicity tends to last longer in dyskinetic cerebral palsy than in spastic types. On passive motion of hypotonic muscles or extremities, no resistance is felt. The infant with generalized hypotonia is limp and floppy with handling and, in severe cases, may feel like a “rag doll”—a descriptive term for this finding. In hypotonia related to motor unit disease or lower motor neuron lesion, deep tendon reflexes are diminished or absent. In contrast, they are present or increased in floppy infants during the transient hypotonic phase of central nervous system damage (l5).
Spastic hypertonicity and related postures are influenced by position in space and the effect of gravity.
The child should be examined in supine, prone, and vertical positions to elicit typical postures. Examples include increased scissoring, extension, and plantar flexion of the legs when a child with spastic cerebral palsy is suddenly lifted into vertical suspension. Resistance to both slow and fast stretching of muscle should be tested to differentiate rigidity from spasticity (l6). In infants and young children, one may use a number of developmental reflexes to examine active movements and strength (l7). The Moro reflex includes shoulder abduction followed by forward flexion of the arm. Eliciting palmar or plantar grasp reflexes demonstrates finger or toe flexor function. Asymmetric responses in the upper extremities may suggest Erb's or Klumpke's paralysis or hemiplegia. Unilateral or bilateral absence of protective extension response is likewise suggestive of weakness in the respective extremity. A four-month-old infant elevates the head and trunk on extended arms in the prone position. Scapular winging during this activity is a sign of a weak serratus anterior muscle (18). In older children, the wheelbarrow maneuver demonstrates the same finding (18). Lifting up under the axilla elicits spontaneous active shoulder depression. When these muscles are weak, the shoulders slide upward, virtually touching the ears. These signs suggest myopathy with proximal weakness.Young children often adopt ingenious substitutions or vicarious movements to cope with weakness of particular muscles. With weakness of the deltoid, they may fling the arm forward by momentum or substitute the long head of the biceps for shoulder flexion. In advanced shoulder and elbow weakness, they may “walk up” the arm on the torso, using their fingers to get the hand to the mouth. Combat crawl is a usual way of crawling in lower extremity paralysis. Deformities around a joint reflect an imbalance of strength in muscles acting on the joint. The deformity or deviation is in the direction of over-pull. Such imbalance may be spastic or paralytic.
Visual observation during performance of functional activities to detect muscle weakness should consider the child's age and the achievements expected for the child's developmental stage. Walking on tiptoes, squatting and rising without using the arms for assistance, and straight sitting up from the supine position without rolling to the prone position or to the side are mastered by children around three years of age (19). Thus, inability of younger children to perform these activities in a mature pattern should not be interpreted as weakness of the plantar flexors, hip and knee extensors, or abdominal muscles. Testing for Trendelenburg's sign and grading the triceps surae by having the child rise on the toes of one leg must be deferred until four years of age, when children develop adequate balance.
The standard technique of manual muscle testing can be used after school age, except in children who have serious behavioral problems or mental retardation (20-23). The customary grading system of scores from 0-5 or zero to normal is used. Above fair grade, the wide range of normal variations in growth patterns should be considered in judging good versus normal strength. Because children are adept in using substitution movements, the examiner must pay special attention and adhere to precise technical conduct of testing individual muscles. Side-to-side comparison may detect even mild neurologic weakness, although disuse atrophy or mild bilateral neurologic weakness may escape detection. Quantitative strength determination with comparison of both sides is helpful to demonstrate unilateral disuse atrophy in such strong muscles as the quadriceps. This determination is particularly advisable in teenage athletes after knee injury. Resumption of training for competition before virtually equal bilateral quadriceps strength is regained predisposes to recurrent injuries. Testing of strength in upper motor neuron lesions requires the well-known considerations for position in space and orientation of head and major joints, which may affect recruitment of motor units and produce synergistic movement patterns.
A common sign of central movement disorders is impaired coordination. Proprioceptive sensory loss or parietal lobe syndrome may contribute to incoordination. Movement abnormalities associated with cerebellar dysfunction, basal ganglion disease, dyskinetic disorders, or spastic incoordination present with specific distinguishing signs. Detection of coordination deficit is based mostly on observation of gross and fine motor function in children less than two to three years of age. Concurrent mild delay of motor development is not unusual. After three years of age, the examination becomes more specific for testing the quality of performance in complex and more advanced developmental skills. Around three years of age, the child can walk along a straight line, unsteadily placing one foot in front of the other. In comparison, facility at tandem walking at five years of age is a good illustration of continuing refinement of motor skills with age. The pediatric physiatrist may be asked to evaluate the appropriateness of coordination in children without an overt physical disability (24). Clumsiness of handwriting and drawing, difficulties in physical education or sports, and other subtle signs may be present. Such children may have a motor incompetence of apraxic nature, sometimes related to visuomotor perceptual deficit (25). It also may be associated with learning and behavioral dysfunction. A number of tests are available for examining motor proficiency and dexterity in children without physical disability (26,27). Tasks to evaluate youngsters with minor neurologic dysfunction include imitation of gestures (28), hopping (29), hand-clapping (30), and pegboard performance (31,32).