Paralysis that remains confined to three limbs is observed only rarely; more often the fourth limb is weak or hyperreflexic, and the syndrome is really an incomplete tetraplegia. As indicated earlier, this pattern of involvement is important, because it may signify an evolving lesion of the upper cervical cord or cervicomedullary junction. A meningioma of the foramen magnum, for example, may begin with spastic weakness of one limb, followed by sequential involvement of the other limbs in the above noted “around-the-clock” pattern. There are usually bilateral Babinski signs early in the process, but there may be few sensory findings. We have also seen this pattern in patients with multiple sclerosis and other intrinsic inflammatory and neoplastic lesions. These same diseases may produce triplegia (or triparesis) by a combination of paraplegia from a thoracic spinal cord lesion and a separate unilateral lesion in the cervical cord or higher that results in a hemiparesis.
Paralysis of Isolated Muscle Groups
This pattern usually indicates a lesion of one or more peripheral nerves or of several adjacent spinal roots. The diagnosis of an individual peripheral nerve lesion is made on the basis of weakness or paralysis of a particular muscle or group of muscles and impairment or loss of sensation in the distribution of the nerve. Complete or extensive interruption of a peripheral nerve is followed by atrophy of the muscles it innervates and by loss of tendon reflexes of the involved muscles; abnormalities of vasomotor and sudomotor functions and trophic changes in the skin, nails, and subcutaneous tissue may occur if the condition has been chronic.
Detailed knowledge of the motor and sensory innervation of the peripheral nerve in question is needed for a diagnosis. It is impractical to memorize the precise sensorimotor distribution of each peripheral nerve and special manuals, such as Aids to the Examination of the Peripheral Nervous System, should be consulted (see also Table 43-1). Electromyography and nerve conduction studies are of great value for localization and to determine if the axon has been damaged or the process affects mainly myelin.
If there is no evidence of upper or lower motor neuron disease but certain movements are nonetheless imperfectly performed, one should look for a disorder of position sense or cerebellar coordination or for rigidity with abnormalities of posture and movement due to disease of the basal ganglia (Chap. 4). In the absence of these disorders, the possibility of an apraxic disorder should be investigated by the methods outlined earlier.
Psychogenic (Hysterical, Conversion)
Psychogenic paralysis may involve one arm or leg, both legs, or all of one side of the body. Tendon reflexes are of normal amplitude, there is no Babinski sign, and atrophy is lacking, features that distinguish it from chronic lower motor neuron disease. Diagnostic difficulty arises only in certain acute cases of upper motor neuron disease that lack the usual changes in reflexes and muscle tone. Sometimes there is loss of sensation in the paralyzed parts and loss of sight, hearing, and smell on the paralyzed side—a pattern of sensory changes that cannot be explained on the basis of organic disease of the nervous system. When the hysterical patient is asked to move the affected limbs, the movements tend to be slow, hesitant, and jerky, often with contraction of agonist and antagonist muscles simultaneously and intermittently (“give-way” weakness). Lack of effort is usually obvious, despite facial and other expressions to the contrary. Power of contraction improves with encouragement and the weakness is inconsistent; some movements are performed tentatively and moments later another movement involving the same muscles is performed naturally.