This is a chronic disease characterized by slow and insidious weakness and wasting of groups of muscles from disease of the anterior spinal grey matter. It begins mostly between 25 and 45 years of age, and affects males more than females. Usually it commences in the upper limbs, and the small muscles of the hand are especially liable to be affected. The muscles next most liable to atrophy are those of the shoulder and upper arm, and the atrophy may thence spread to the neck and trunk, and the intercostals and even the diaphragm may be affected, causing serious difficulties of respiration. The lower ex tremities are less often and later affected. This disease generally runs a slow and progressive course. A characteristic feature is fibrillary twitching of the wasting muscles. The electrical excit ability of the muscles is diminished rather than changed, except where the wasting is extreme, when a partial reaction of degenera tion may be obtained. Sensation is unaffected. There is no affection of the bowel or bladder. Death usually occurs from inter current diseases, e.g., bronchitis, pneumonia or bronchopneumo nia. Some patients die owing to failure of the respiratory muscles; others from the disease spreading to the medulla oblongata (the bulb of the brain) and causing bulbar paralysis. The destruction of spinal motor cells which is the essential pathological feature of this disease is generally accompanied, and sometimes preceded, by degeneration of the path of voluntary impulses from the brain. It is then called amyotrophic lateral sclerosis, a rapid form of progressive muscular atrophy.
Various morbid conditions may give rise to a group of symptoms, the principal features of which are paralysis of the muscles concerned in speech, swallowing, phona tion and mastication. These symptoms may arise suddenly from vascular lesions or inflammatory processes, which involve the nuclei of origin of the cranial nerves supplying the muscles of the tongue, lips, pharynx and larynx. But there is also a slow degenerative insidious progressive bulbar paralysis affecting both sexes pretty equally ; it comes on between 4o and 6o years of age, and the cause is unknown. Slight indistinctness of speech is usually the first symptom. Later, owing to paralysis of the soft palate, the speech becomes nasal in character. Sooner or later there is a difficulty of swallowing, and liquids are apt to re gurgitate through the nostrils. As the disease proceeds, the laryn geal muscles become affected; the pitch of the voice is lowered and the glottis is imperfectly closed during deglutition; there is consequently a tendency for liquids and food to pass into the larynx and set up fits of coughing. Later the muscles of mastica tion are affected and the disease may extend to the respiratory centre. The intellectual faculties are as a rule unimpaired, although the facial expression and the curious emotional mobility of the countenance, would suggest weak-mindedness. Whilst the
lower half of the face is strikingly affected, the upper half re tains its normal expression and power of movement. This disease is usually rapidly fatal.
con dition is also termed "myasthenia gravis"; it differs from acute and chronic bulbar disease by the absence of muscular atrophy, normal electrical excitability of the muscles, marked development of the paralysis by fatigue, and considerable remissions of the symptoms. The bulbar symptoms are the most prominent, but all voluntary muscles are more or less affected.
Paralysis may result further from disease or injury of the motor path to the muscles in the peripheral nervous system.
Paralysis may arise in a muscle, a group of muscles, a whole limb, the lower extremities, or there may be a general ized paralysis of voluntary muscles as a result of neuritis. A typical example of neuritis giving rise to paralysis owing to in flammatory swelling and compression is afforded by the facial nerve ; this purely motor nerve as it passes out of the skull through a narrow bony passage is easily compressed and its function interfered with, causing a paralysis of the whole of one side of the face and Bell's Palsy. Exposure to a cold draught in a person with rheumatic diathesis is a frequent cause.
Lead poisoning (q.v.) may give rise to a localized neuritis affecting the posterior inter-osseous nerve, especially in painters and in those whose occupations necessitate excessive use of the extensors of the forearm ; the result is wrist drop or lead palsy. Sciatica and Multiple Neuritis.—Sciatica is a painful in flammatory condition of the sciatic nerve, in which there may be weakness of the muscles; but inability to move the limb is more on account of the pain it causes than on account of paralysis of the muscles. Exposure to cold and wet, e.g., sitting on a damp seat, may lead to sciatica in a gouty or rheumatic person.
Multiple neuritis (see NEURITIS) is a painful generalized in flammation of the peripheral nervous system and arises in many toxic conditions of the blood ; among the most important are lead, arsenic and chronic alcohol poisoning. It also occurs in diabetes, diphtheria and beriberi (see NEUROPATHOLOGY).
Paralysis—termed medically muscular dystrophies—may arise from a primary atrophy of muscle apparently independent of any discoverable change in the nervous system, but due to a congenital developmental defect of the muscles. Heredity plays an important part in the incidence of these diseases. There may be a tendency in a family to the affection of one sex and not the other; on the other hand, children of both sexes may suffer in the same family. It is curious that the majority of cases are males, and that it is transmitted by women who are not them selves its subjects.