Amyotrophic lateral sclerosis (ALS) is a progressive disease that affects motor neurons, which are specialized nerve cells that control muscle movement. These nerve cells are found in the spinal cord and the brain. In ALS, motor neurons die (atrophy) over time, leading to muscle weakness, a loss of muscle mass, and an inability to control movement.\n\nThere are many different types of ALS; these types are distinguished by their signs and symptoms and their genetic cause or lack of clear genetic association. Most people with ALS have a form of the condition that is described as sporadic, which means it occurs in people with no apparent history of the disorder in their family. People with sporadic ALS usually first develop features of the condition in their late fifties or early sixties. A small proportion of people with ALS, estimated at 5 to 10 percent, have a family history of ALS or a related condition called frontotemporal dementia (FTD), which is a progressive brain disorder that affects personality, behavior, and language. The signs and symptoms of familial ALS typically first appear in one's late forties or early fifties. Rarely, people with familial ALS develop symptoms in childhood or their teenage years. These individuals have a rare form of the disorder known as juvenile ALS.\n\nThe first signs and symptoms of ALS may be so subtle that they are overlooked. The earliest symptoms include muscle twitching, cramping, stiffness, or weakness. Affected individuals may develop slurred speech (dysarthria) and, later, difficulty chewing or swallowing (dysphagia). Many people with ALS experience malnutrition because of reduced food intake due to dysphagia and an increase in their body's energy demands (metabolism) due to prolonged illness. Muscles become weaker as the disease progresses, and arms and legs begin to look thinner as muscle tissue atrophies. Individuals with ALS eventually lose muscle strength and the ability to walk. Affected individuals eventually become wheelchair-dependent and increasingly require help with personal care and other activities of daily living. Over time, muscle weakness causes affected individuals to lose the use of their hands and arms. Breathing becomes difficult because the muscles of the respiratory system weaken. Most people with ALS die from respiratory failure within 2 to 10 years after the signs and symptoms of ALS first appear; however, disease progression varies widely among affected individuals.\n\nApproximately 20 percent of individuals with ALS also develop FTD. Changes in personality and behavior may make it difficult for affected individuals to interact with others in a socially appropriate manner. Communication skills worsen as the disease progresses. It is unclear how the development of ALS and FTD are related. Individuals who develop both conditions are diagnosed as having ALS-FTD.\n\nA rare form of ALS that often runs in families is known as ALS-parkinsonism-dementia complex (ALS-PDC). This disorder is characterized by the signs and symptoms of ALS, in addition to a pattern of movement abnormalities known as parkinsonism, and a progressive loss of intellectual function (dementia). Signs of parkinsonism include unusually slow movements (bradykinesia), stiffness, and tremors. Affected members of the same family can have different combinations of signs and symptoms.

A series of rhythmic and involuntary muscle contractions (at a frequency of about 5 to 7 Hz) that occur in response to an abruptly applied and sustained stretch.

Upturning of the big toe (and sometimes fanning of the other toes) in response to stimulation of the sole of the foot. If the Babinski sign is present it can indicate damage to the corticospinal tract.

Hyperreflexia is the presence of hyperactive stretch reflexes of the muscles.

Fine, rapid twitching of individual muscle fibers with little or no movement of the muscle as a whole. If a motor neuron or its axon is destroyed, the muscle fibers it innervates undergo denervation atrophy. This leads to hypersensitivity of individual muscle fibers to acetyl choline so that they may contract spontaneously. Isolated activity of individual muscle fibers is generally so fine it cannot be seen through the intact skin, although it can be recorded as a short-duration spike in the EMG.

Any structural anomaly of the lower motor neuron.

An abnormally pale appearance of the dorsal portion of the gray substance of the spinal cord. This finding can be observed by histological examination.

Progressive deterioration of peripheral axons.

Reduced level of the compound muscle action potential (CMAP), which is recorded following electrical stimulation of a nerve from surface electrodes overlying a muscle supplied by that nerve.

Reduced ability to walk (ambulate).

Reduced strength of the musculature of the distal extremities.

These are spontaneous firing action potentials stimulated by needle movement of an injured muscle fiber. There is propagation to, but not past, the needle tip. This inhibits the display of the negative deflection of the waveform.

Muscular atrophy affecting muscles in the distal portions of the extremities.