medicine   doctors   home page

motor neuron disease

Motor Neuron Diseases



What are the symptoms of motor neuron diseases?

Below is a brief description of the symptoms of some of the more common motor neuron diseases:

Amyotrophic lateral sclerosis (ALS), also called Lou Gehrig's disease or classical motor neuron disease, is a progressive, ultimately fatal disorder that eventually disrupts signals to all voluntary muscles. In the United States, doctors use the terms motor neuron disease and ALS interchangeably. Both upper and lower motor neurons are affected. Approximately 75 percent of people with classic ALS will also develop weakness and wasting of the bulbar muscles (muscles that control speech, swallowing, and chewing).

Symptoms are usually noticed first in the arms and hands, legs, or swallowing muscles. Muscle weakness and atrophy occur disproportionately on both sides of the body. Affected individuals lose strength and the ability to move their arms, legs, and body. Other symptoms include spasticity, exaggerated reflexes, muscle cramps, fasciculations, and increased problems with swallowing and forming words. Speech can become slurred or nasal. When muscles of the diaphragm and chest wall fail to function properly, individuals lose the ability to breathe without mechanical support. Although the disease does not usually impair a person's mind or personality, several recent studies suggest that some people with ALS may have alterations in cognitive functions such as problems with decision-making and memory.

ALS most commonly strikes people between 40 and 60 years of age, but younger and older people also can develop the disease. Men are affected more often than women. Most cases of ALS occur sporadically, and family members of those individuals are not considered to be at increased risk for developing the disease. (There is a familial form of ALS in adults, which often results from mutation of the superoxide dismutase gene, or SOD1, located on chromosome 21.)

A rare juvenile-onset form of ALS is genetic. Most individuals with ALS die from respiratory failure, usually within 3 to 5 years from the onset of symptoms. However, about 10 percent of affected individuals survive for 10 or more years.

Progressive bulbar palsy, also called progressive bulbar atrophy, involves the bulb-shaped brain stem —the region that controls lower motor neurons needed for swallowing, speaking, chewing, and other functions.

Symptoms include pharyngeal muscle weakness (involved with swallowing), weak jaw and facial muscles, progressive loss of speech, and tongue muscle atrophy. Limb weakness with both lower and upper motor neuron signs is almost always evident but less prominent. Affected persons have outbursts of laughing or crying (called emotional liability). Individuals eventually become unable to eat or speak and are at increased risk of choking and aspiration pneumonia, which is caused by the passage of liquids and food through the vocal folds and into the lower airways and lungs.

Stroke and myasthenia gravis each have certain symptoms that are similar to those of progressive bulbar palsy and must be ruled out prior to diagnosing this disorder. In about 25 percent of ALS cases early symptoms begin with bulbar involvement. Some 75 percent of individuals with classic ALS eventually show some bulbar involvement. Many clinicians believe that progressive bulbar palsy by itself, without evidence of abnormalities in the arms or legs, is extremely rare.



Pseudobulbar palsy, which shares many symptoms of progressive bulbar palsy, is characterized by upper motor neuron degeneration and progressive loss of the ability to speak, chew, and swallow. Progressive weakness in facial muscles leads to an expressionless face. Individuals may develop a gravelly voice and an increased gag reflex. The tongue may become immobile and unable to protrude from the mouth. Individuals may also experience emotional liability.

Primary lateral sclerosis (PLS) affects only upper motor neurons and is nearly twice as common in men as in women. Onset generally occurs after age 50. The cause of PLS is unknown. It occurs when specific nerve cells in the cerebral cortex (the thin layer of cells covering the brain which is responsible for most higher level mental functions) that control voluntary movement gradually degenerate, causing the muscles under their control to weaken.

The syndrome which scientists believe is only rarely hereditary, progresses gradually over years or decades, leading to stiffness and clumsiness of the affected muscles. The disorder usually affects the legs first, followed by the body trunk, arms and hands, and, finally, the bulbar muscles. Symptoms may include difficulty with balance, weakness and stiffness in the legs, clumsiness, spasticity in the legs which produces slowness and stiffness of movement, dragging of the feet (leading to an inability to walk), and facial involvement resulting in dysarthria (poorly articulated speech).

Major differences between ALS and PLS (considered a variant of ALS) are the motor neurons involved and the rate of disease progression. PLS may be mistaken for spastic paraplegia, a hereditary disorder of the upper motor neurons that causes spasticity in the legs and usually starts in adolescence. Most neurologists follow the affected individual's clinical course for at least 3 years before making a diagnosis of PLS. The disorder is not fatal but may affect quality of life. PLS often develops into ALS.

Progressive muscular atrophy is marked by slow but progressive degeneration of only the lower motor neurons. It largely affects men, with onset earlier than in other MNDs. Weakness is typically seen first in the hands and then spreads into the lower body, where it can be severe. Other symptoms may include muscle wasting, clumsy hand movements, fasciculations, and muscle cramps. The trunk muscles and respiration may become affected. Exposure to cold can worsen symptoms. The disease develops into ALS in many instances.

Spinal muscular atrophy (SMA) is a hereditary disease affecting the lower motor neurons. Weakness and wasting of the skeletal muscles is caused by progressive degeneration of the anterior horn cells of the spinal cord. This weakness is often more severe in the legs than in the arms. SMA has various forms, with different ages of onset, patterns of inheritance, and severity and progression of symptoms. Some of the more common SMAs are described below.

SMA type I, also called Werdnig-Hoffmann disease, is evident by the time a child is 6 months old. Symptoms may include hypotonia (severely reduced muscle tone), diminished limb movements, lack of tendon reflexes, fasciculations, tremors, swallowing and feeding difficulties, and impaired breathing. Some children also develop scoliosis (curvature of the spine) or other skeletal abnormalities. Affected children never sit or stand and the vast majority usually die of respiratory failure before the age of 2.

Symptoms of SMA type II usually begin after the child is 6 months of age. Features may include inability to stand or walk, respiratory problems, hypotonia, decreased or absent tendon reflexes, and fasciculations. These children may learn to sit but do not stand. Life expectancy varies, and some individuals live into adolescence or later.

Symptoms of SMA type III (Kugelberg-Welander disease) appear between 2 and 17 years of age and include abnormal gait; difficulty running, climbing steps, or rising from a chair; and a fine tremor of the fingers. The lower extremities are most often affected. Complications include scoliosis and joint contractures—chronic shortening of muscles or tendons around joints, caused by abnormal muscle tone and weakness, which prevents the joints from moving freely.

Symptoms of Fazio-Londe disease appear between 1 and 12 years of age and may include facial weakness, dysphagia (difficulty swallowing), stridor (a high-pitched respiratory sound often associated with acute blockage of the larynx), difficulty speaking (dysarthria), and paralysis of the eye muscles. Most individuals with SMA type III die from breathing complications.

Kennedy disease, also known as progressive spinobulbar muscular atrophy, is an X-linked recessive disease. Daughters of individuals with Kennedy disease are carriers and have a 50 percent chance of having a son affected with the disease. Onset occurs between 15 and 60 years of age. Symptoms include weakness of the facial and tongue muscles, hand tremor, muscle cramps, dysphagia, dysarthria, and excessive development of male breasts and mammary glands. Weakness usually begins in the pelvis before spreading to the limbs. Some individuals develop noninsulin-dependent diabetes mellitus.

The course of the disorder varies but is generally slowly progressive. Individuals tend to remain ambulatory until late in the disease. The life expectancy for individuals with Kennedy disease is usually normal.

Congenital SMA with arthrogryposis (persistent contracture of joints with fixed abnormal posture of the limb) is a rare disorder. Manifestations include severe contractures, scoliosis, chest deformity, respiratory problems, unusually small jaws, and drooping of the upper eyelids.



Post-polio syndrome (PPS) is a condition that can strike polio survivors decades after their recovery from poliomyelitis. PPS is believed to occur when injury, illness (such as degenerative joint disease), weight gain, or the aging process damages or kills spinal cord motor neurons that remained functional after the initial polio attack. Many scientists believe PPS is latent weakness among muscles previously affected by poliomyelitis and not a new MND.

Symptoms include fatigue, slowly progressive muscle weakness, muscle atrophy, fasciculations, cold intolerance, and muscle and joint pain. These symptoms appear most often among muscle groups affected by the initial disease. Other symptoms include skeletal deformities such as scoliosis and difficulty breathing, swallowing, or sleeping. Symptoms are more frequent among older people and those individuals most severely affected by the earlier disease.

Some individuals experience only minor symptoms, while others develop SMA and, rarely, what appears to be, but is not, a form of ALS. PPS is not usually life threatening. Doctors estimate the incidence of PPS at about 25 to 50 percent of survivors of paralytic poliomyelitis.