Chapter 599 Evaluation and Investigation
Clinical Manifestations
Examination of the neuromuscular system includes an assessment of muscle bulk, tone, and strength. Tone and strength should not be confused: Passive tone is range of motion around a joint; active tone is physiologic resistance to movement. Head lag when an infant is pulled to a sitting position from supine is a sign of weakness, not of low tone. Hypotonia may be associated with normal strength or with weakness; enlarged muscles may be weak or strong; thin, wasted muscles may be weak or have unexpectedly normal strength. The distribution of these components is of diagnostic importance. In general, myopathies follow a proximal distribution of weakness and muscle wasting (with the notable exception of myotonic muscular dystrophy); neuropathies are generally distal in distribution (with the notable exception of juvenile spinal muscular atrophy; Table 599-1). Involvement of the face, tongue, palate, and extraocular muscles provides an important distinction in the differential diagnosis. Tendon stretch reflexes are generally lost in neuropathies and in motor neuron diseases and are diminished but preserved in myopathies (see Table 599-1). A few specific clinical features are important in the diagnosis of some neuromuscular diseases. Fasciculations of muscle, which are often best seen in the tongue, are a sign of denervation. Sensory abnormalities indicate neuropathy. Fatigable weakness is characteristic of neuromuscular junctional disorders. Myotonia is specific for a few myopathies.
Generalized hypotonia and motor developmental delay are the most common presenting manifestations of neuromuscular disease in infants and young children (Table 599-2). These features can also be expressions of neurologic disease, endocrine and systemic metabolic diseases, and Down syndrome, or they may be nonspecific neuromuscular expressions of malnutrition or chronic systemic illness (Table 599-3). A prenatal history of decreased fetal movements and intrauterine growth retardation is often found in patients who are symptomatic at birth. Developmental disorders tend to be of slow onset and are progressive. Acute flaccid paralysis in older infants and children has a different differential diagnosis (Table 599-4).
Table 599-2 PATTERN OF WEAKNESS AND LOCALIZATION IN THE FLOPPY INFANT
ANATOMIC REGION OF HYPOTONIA | CORRESPONDING DISORDERS |
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