Poliomyelitis

Poliomyelitis is an acute viral infection. Initially it may cause only a brief, febrile illness, but groups of ventral-horn cells of the spinal cord may be destroyed. This may later cause severe pain with further fever, occasional delirium and meningism (due to accompanying encephalitis), and a rapid onset of muscle atrophy, fasciculations, and weakness that may be localized or diffuse, mild or profound, and that may be fatal if the respiratory or bulbar muscles are involved. Only supportive treatment is available for poliomyelitis, but some recovery occurs in the majority of patients who survive the acute stage of the illness. Since the advent of immunization programs in the 1950s, this disease has been rare in the Western world.

 
Hereditary motor neuropathies

Hereditary motor neuropathies (also known as spinal muscular atrophies and as Werdnig-Hoffman or Kugelberg-Welander diseases) are a diverse group of genetic disorders in which signs of ventral-horn disease occur in babies or young people. The usual symptoms of muscle atrophy and weakness progress more slowly if the disease begins at a later age (5 to 15 years); at later ages the disease may also pass, leaving only chronic mild weakness and secondary skeletal deformities such as scoliosis (rotation of the spine). Less commonly, muscle weakness occurs in specific patterns—for example, involving only the facial, shoulder, or calf muscles—and the progress of the disease is much slower. Babies with these disorders may exhibit respiratory insufficiency, poor ability to suck, and severe limpness and weakness of all muscles except those of the face and eyes; the muscles of the shoulder and pelvic girdles are primarily affected. Motor development is delayed or absent. Diagnosis of hereditary motor neuropathy is confirmed by electromyography and muscle biopsy. Enzyme deficiencies are the cause of some cases of hereditary motor neuropathy, but in most cases the etiological basis of the disease is unknown.

 
Motor neuron disease

Amyotrophic lateral sclerosis (ALS) and lateral sclerosis are both motor neuron diseases, progressive disorders of older people that affect neurons of the ventral horns, of the medullary motor nuclei, and of the corticospinal tracts. ALS, or Lou Gehrig disease, is characterized by muscle wasting due to loss of the ventral-horn cells (the lower motor neurons). Lateral sclerosis is the loss of axons in the lateral columns of the spinal cord (the upper motor neurons of the corticospinal tracts). A combination of upper and lower motor neuron signs is associated with these diseases, but muscle weakness and atrophy of two or more limbs is the primary feature. The brain, eyes, and sensory system are unaffected.

 
Nerve injuries

Nerve injuries function as neuronal neuropathies affecting the axon far from the cell body. Injuries are of three main grades of severity. In neurapraxia there is temporary blockage of impulse conduction, although the axons remain intact. More severe stretch or incision damage interrupts some axons and is called axonotmesis. Injury that actually severs the nerve is called neurotmesis; surgical reattachment of the severed nerve ends is necessary. Neurosurgery does not guarantee a rapid recovery, since new nerve sprouts grow down the nerve framework at the rate of 1 to 2 mm (0.04 to 0.08 inch) per day at most.