Motor Neuron Disease: Classification and Symptoms

An Introduction To MND

Motor neuron disease (MND) results in degeneration of the upper and lower motor neurons. Lower motor neuron disease is more prevalent in men over fifty years of age. It is an aggressive condition that can result in death from respiratory dysfunction.

Juvenile Motor Neuron Disease

In children, this is known as spinal muscular atrophy (SMA) and the condition is autosomally recessive, with both parents having to be carriers for a baby to be born with this disease. There is widespread muscle atrophy, sometimes with loss of the entire muscle fiber. The most prevalent form is Werdnig Hoffman disease. During the first few months of life, the baby’s muscles have no tone, which is called “floppy infant.” This is the main characteristic of this condition. Death will usually occur before age five.

Adult Types of Motor Neuron Disease

The most common adult type is amylotrophic lateral sclerosis or ALS. This is also known as Lou Gehrig’s disease, named for the famous baseball player who had the condition. It involves both upper and lower motor neurons. There is wasting of muscles as the muscles atrophy, leading to weakness and fatigue. The condition is mainly in the hands and feet, so a person with ALS will constantly drop things or trip over his feet. The life expectancy after diagnosis is two to five years.

The second type in the adult group is primary lateral sclerosis (PLS). This disease is rare and only involves the upper motor neurons so the upper limbs, facial expressions, and speech are affected.

Progressive bulbar palsy (PBP) also belongs to this group, and like ALS, it has both upper and lower motor neuron involvement. This condition has one of the shortest life spans after first diagnosis, with a life expectancy of three months to three years. The symptoms of PBP involve the muscles innervated by the cranial bulbar nerve. Therefore, there will be slurred speech and difficulty swallowing or chewing.

The last type is progressive muscular atrophy (PMA). PMA is also one of the least common types within this group. It only involves the lower motor neurons, so the arms and hands will be affected.

Symptoms and General Outcome of MND

The general symptoms and signs of motor neuron disease involve skeletal and muscular system changes. There will be muscle atrophy, muscle cramps, pain, and stiffness in joints. If the urinary system is affected, the person will have incontinence. However, the danger of this disease is seen in skeletal muscle involvement resulting in gasping, choking, and difficulty breathing, which leads to death.

References

Print Source: Davidson, Stanley & C. Haslett. 2002. “Davidson’s Principles and Practice of Medicine.” Churchill Livingstone, Edinburgh.

Web Source: National Institute of Neurological Disorders & Stroke. “NINDS Motor Neuron Diseases Information Page.” 2009. Available: https://www.ninds.nih.gov/disorders/motor_neuron_diseases/motor_neuron_diseases.htm