ALS vs Muscular Dystrophy: A Comparative Analysis

Introduction to ALS

The American College of Radiology suggests that ALS involves degeneration of both upper and lower motor neurons in the brain and spinal cord along the corticospinal tracts, making it primarily a motor neuron disease rather than a primary muscle disorder 1, 2
ALS is the most common motor neuron disease, representing approximately 85% of all motor neuron disease cases 1, 2
The majority of ALS cases (85-90%) are sporadic, with an annual incidence of 1-2 per 100,000 people 1, 2
Mean survival of ALS patients is typically 3-5 years after symptom onset, with only 5-10% living longer than 10 years 3

ALS is characterized by progressive loss of motor neurons, resulting in atrophy of skeletal muscles including respiratory muscles 4, 3
The etiology is multifactorial, involving increased oxidative stress 3, glutamate toxicity 3, mitochondrial dysfunction 3, inflammation 5, and apoptosis 4, 3

Muscular dystrophies are a group of genetic diseases characterized by progressive weakness and degeneration of the skeletal muscles that control movement 5
Typical histopathologic features of muscular dystrophy include reduction or absence of dystrophin 5, degenerating and regenerating muscle fibers 5, and replacement of muscle with fat or connective tissue 5
Muscular dystrophies are primarily caused by mutations in genes responsible for muscle structure and function, particularly the dystrophin gene 5

Almost 80% of ALS patients with bulbar onset develop dysarthria and dysphagia 3
Muscular dystrophy typically presents with progressive proximal muscle weakness 5
Muscular dystrophy often has onset in childhood or adolescence (though some forms can present in adulthood) 5
Muscular dystrophy usually lacks the upper motor neuron signs (hyperreflexia, spasticity) seen in ALS 5
Muscular dystrophy does not typically affect bulbar muscles early in the disease course 5

Electromyography (EMG) and nerve conduction velocity studies are key tests in diagnosing ALS 1, 2
MRI of the brain and spine is used mainly to exclude other conditions rather than confirm ALS 1, 2
Common MRI findings in ALS include abnormal T2/FLAIR signal in the corticospinal tracts 2, and abnormal T2/short tau inversion recovery signal in the anterior horns ("snake eyes" appearance) in the spine 1, 2
Muscle biopsy showing characteristic histopathologic features is used to diagnose muscular dystrophy 5
Genetic testing for specific muscular dystrophy genes is used to diagnose muscular dystrophy 5
Elevated creatine kinase levels in blood are often seen in muscular dystrophy 2
Absence of upper motor neuron signs is a characteristic feature of muscular dystrophy 5