From the Guidelines
Motor neuron diseases are a group of progressive neurological disorders that include Amyotrophic Lateral Sclerosis (ALS), Primary Lateral Sclerosis (PLS), Progressive Muscular Atrophy (PMA), Spinal Muscular Atrophy (SMA), Kennedy's Disease, and Post-Polio Syndrome. The main types of motor neuron diseases can be categorized based on the motor neurons they affect:
- Amyotrophic Lateral Sclerosis (ALS) affects both upper and lower motor neurons, leading to paralysis and respiratory failure within 3-5 years 1.
- Primary Lateral Sclerosis (PLS) primarily affects upper motor neurons, causing stiffness and weakness but progressing more slowly than ALS.
- Progressive Muscular Atrophy (PMA) targets lower motor neurons, leading to muscle weakness and atrophy, particularly in the hands and legs.
- Spinal Muscular Atrophy (SMA) is a genetic disorder affecting lower motor neurons, with several types based on age of onset and severity.
- Kennedy's Disease (Spinal and Bulbar Muscular Atrophy) is an X-linked genetic disorder affecting men, causing weakness in facial and limb muscles.
- Post-Polio Syndrome can develop decades after polio infection, with progressive muscle weakness. These conditions occur when motor neurons degenerate and die, disrupting signals between the brain and muscles, though the exact causes vary from genetic mutations to environmental factors and possibly autoimmune mechanisms 1. The diagnosis of motor neuron diseases often involves a combination of clinical evaluation, electromyography, nerve conduction velocity, and imaging studies to exclude other conditions with similar clinical presentations 1.
From the Research
Types of Motor Neuron Diseases
- Amyotrophic Lateral Sclerosis (ALS) is the most common type, comprising 80%-90% of cases 2
- Progressive Myelopathic Muscular Atrophy (PMMA) is another type, characterized by anterior horn cell lesions 3
- Progressive Bulbar Palsy (PBP) is a type that affects the brain stem and cord 3
- Primary Lateral Sclerosis (PLS) is a type characterized by pure upper motor neuron findings, with a more benign course than classical ALS 4
- Progressive Muscular Atrophy (PMA) is a type of motor neuron disease that is related to ALS 4
- Western Pacific ALS is a distinct type of ALS that is characterized by a higher prevalence in certain geographic regions 4
- ALS-plus syndromes are characterized by the presence of atypical clinical features, such as extrapyramidal signs or dementia, in association with the classical phenotype of ALS 4
- Frontotemporal dementia (FTD) is a condition that can occur in up to 50% of ALS cases, with 10%-15% of patients meeting the clinical criteria for FTD 5
Subtypes of Amyotrophic Lateral Sclerosis
- Bulbar onset ALS, which has a poor prognosis compared to spinal-onset ALS 4
- Limb onset ALS, which has a better prognosis than bulbar-onset ALS 4
- Sporadic ALS, which accounts for 90% of cases and has no clear familial pattern 5
- Familial ALS, which accounts for 10% of cases and has an autosomal dominant inheritance pattern 5