Paralysis. The term paralysis, while ordinarily used to express loss of power of movement, is used medically in the wider sense of loss of function, so that there may be paralysis of motion, of sensation, of secretion, &c. The term Paresis is used to indicate a diminished activity of function. Thus, paresis of a limb means diminished power of moving the limb.
From what is said under the articles BRAIN, NERVOUS SYSTEM, and SPINAL CORD it will be seen that paralysis may arise (1) from destruction of the nerve-cells in the motor area of the surface of the brain; (2) from interruption of the nerve-fibres in their path through the brain to the spinal cord; (3) from interruption of the nerve-fibres in their path through the spinal cord; (4) from disease of the nerve-cells in the spinal cord; (5) from disease or injury to the nerves passing from the spinal cord to the muscles; or (6) from affections of the muscles themselves. Thus, we speak of Cerebral, Spinal, and Peripheral Paralyses.
Cerebral Paralysis.—The most common causes of paralysis from brain disease are the rupture of blood-vessels (see APOPLEXY), or the blocking up of the blood-vessels which pass to the surface of the brain by clots or other solid particles carried from the heart or larger arteries (embolism). Other less frequent causes are tumours, abscesses, &c. The most usual form of paralysis is that termed Hemiplegia, in which there is paralysis of the leg, arm, and muscles of the mouth and tongue on one side of the body, often accompanied, if the disease is on the right side, by the condition called Aphasia (q.v.). If the original condition has been such as merely to produce pressure upon the nerves without their actual destruction, it may be completely recovered from. But this is obviously not very frequent. Hemiplegia may be entirely unaccompanied by any paralysis of sensation, but if the fibres which carry sensory impulses to the surface of the brain be also destroyed there will be a concomitant loss of sensation on the same side as the loss of motion (hemianæsthesia). In certain cases, when the disease of the brain is in the pons Varolii, the mouth may be paralysed on the opposite side from the paralysed limbs. (This depends on anatomical considerations.) Destruction by disease of individual 'motor areas' will obviously lead to paralysis of the corresponding movements.
Spinal Paralysis is usually the result either (1) of pressure upon the spinal cord from the results of curvature or injury of the spine, or of growths such as tumours or abscesses; (2) of disease of the spinal cord itself, especially from tumours or acute or chronic inflammations, which may lead to interruption of the nerve-fibres which pass downwards from the brain to the nerve-cells in the gray matter of the spinal cord; or (3) of direct injury to the spinal cord. If the conducting paths from and to the brain are interrupted in any way, there is complete paralysis of voluntary motion and of sensation below the level of the affected part of the spinal cord, because the motor impulses cannot pass down nor the sensory impulses upwards. At the same time, below the injury reflex movements may be preserved and certain forms even increased. Such spinal paralysis is termed Paraplegia. If the injury to the spinal cord is localised to one side there will be paralysis of the muscles on the same side, supplied by the nerves arising from the cord below the injury, and of sensibility of the opposite side of the body below the injury (see SPINAL CORD).
In certain cases the nerve-cells in the anterior horns of the gray matter of the cord (and the same may be said of the corresponding cells of origin of the motor nerves of the brain) may be diseased without implication of any other part of the spinal cord. The result of this is paralysis of the muscles supplied by those nerve-cells, and consequent gradual wasting of the muscles. Under this head come those frequent localised paralyses in the lower limbs of children (the so-called 'essential paralyses' of children) which affect certain groups of muscles, and lead to such deformities as club-foot and impaired growth of the limbs. A similar disease is sometimes observed in adults (progressive muscular atrophy), which runs a very chronic course and leads to a gradual wasting of muscles, the direct result of a corresponding gradual wasting of the nerve-cells in the gray matter of the cord. The disease called 'bulbar paralysis,' in which there is a slow affection of the muscles of the tongue, of the side of the mouth, and of the larynx, is of this nature, its more rapidly fatal termination being due to the implication of structures so necessary for organic life.
Peripheral Paralyses.—(a) From Affections of Nerves.—These are of extremely frequent occurrence, and may be due to pressure upon, injury to, or disease of the nerves. The most common of these diseases are the inflammations arising from cold, from the excessive use of alcohol, or from exposure to the poison of lead. If the nerve affected be a purely motor nerve the resulting paralysis is purely motor. The typical example is the so-called 'Bell's' or 'facial paralysis,' from affection of the seventh cranial nerve. This arises most commonly either from exposure to draught or from disease of the ear, in the neighbourhood of which the nerve passes through the bones of the skull (see EAR). There results a complete paralysis of the muscles of expression on the corresponding side of the face; the mouth is twisted to the opposite side, the lips cannot be pursed or retracted, the eye cannot be shut, and the forehead can be neither raised nor depressed, while the usual furrows on the forehead and cheek are either obliterated or diminished. The disease is in many cases amenable to treatment, but when associated with disease of the ear it should always be regarded as of grave import. If proper treatment be neglected, the paralysed muscles may waste, and recovery become impossible. 'Lead palsy' is usually indicated by a loss of the power of extending the wrists (wrist-drop) without impairment of sensation (see LEAD-POISONING). An example of paralysis resulting from pressure on a nerve is seen in the not uncommon result of sleeping with the arms over the back of a chair (sleeping or crutch palsy). As the musculo-spinal nerve is compressed, and the muscles which it supplies—namely, those which extend the wrist and fingers, and which turn the forearm outwards (supination)—are paralysed, there is a wrist-drop like that of lead palsy, but in addition there is loss of sensibility (anaesthesia) on the skin of the back of the thumb and first two fingers. (b) From Disease of Muscles.—A very remarkable form of paralysis—affecting mostly the young—is that termed 'pseudo-hypertrophic paralysis,' in which the onset of the paralysis, which is very gradual, is accompanied by a remarkable apparent overgrowth of the muscles, more especially in the calves of the legs, in the thighs, and back. Examination of the muscles shows that the special muscular tissue is replaced by fat, while the nerves themselves are apparently not diseased. Injury, such as rupture or bruising of muscle, will produce paralysis, which may be only temporary.
Hysterical Paralysis.—Paralysis, which may for the time being be as complete as in any of the cases above described, may occur without any discoverable lesion. To this the term 'hysterical' has been applied (see Hysteria). The simulation of organic paralysis by hysteria is frequently so close as to deceive even expert observers. See Gowers, Diseases of Spinal Cord and Brain; Quain's Dictionary of Medicine. For 'general paralysis,' see INSANITY, Vol. VI. p. 155.