What is the typical feature seen in ALS (Amyotrophic Lateral Sclerosis)?

Flaccid Quadriparesis is Not a Typical Feature of ALS

The typical feature seen in Amyotrophic Lateral Sclerosis (ALS) is a combination of upper and lower motor neuron signs, with spastic quadriparesis (not flaccid quadriparesis) and without sensory abnormalities. 1, 2

Clinical Presentation of ALS

ALS is characterized by progressive degeneration of both upper motor neurons (UMN) and lower motor neurons (LMN), resulting in a distinctive clinical presentation:

Upper Motor Neuron Signs

• Hypertonicity/spasticity
• Hyperreflexia
• Pyramidal tract signs

Lower Motor Neuron Signs

• Muscle fasciculations
• Weakness
• Muscle atrophy

Key Diagnostic Features

• Progressive muscle weakness and wasting
• Absence of sensory abnormalities (option B is incorrect)
• Combination of UMN and LMN signs in the same body region
• Spread from one body region to others over time

Distinguishing Features from Other Motor Neuron Diseases

ALS must be differentiated from other motor neuron diseases:

• Primary Lateral Sclerosis (PLS): Predominantly UMN involvement with spasticity as the main symptom (47% vs. 4% in ALS) and minimal to no muscle wasting (2% vs. 100% in ALS) 3
• Progressive Muscular Atrophy: Predominantly LMN involvement
• Flaccid Quadriparesis: Not characteristic of ALS but rather seen in conditions affecting primarily LMNs or peripheral nerves 4

Diagnostic Approach

The diagnosis of ALS relies on:

1. Clinical Assessment: Demonstration of both UMN and LMN signs
2. Electromyography (EMG): Key diagnostic test showing:
   • Active denervation
   • Chronic denervation/reinnervation
   • Fasciculations in multiple body regions 2
3. MRI: Primarily to exclude other conditions, may show:
   • Abnormal T2/FLAIR signal in corticospinal tracts
   • "Snake eyes" appearance in anterior horns of the spinal cord 1
4. Swallowing Assessment: Videofluoroscopy often reveals:
   • Delayed bolus transport from oral cavity to pharynx
   • Decreased pharyngeal contraction
   • Pharyngeal residue even in asymptomatic patients 1

Clinical Pitfalls to Avoid

1. Misdiagnosis: Don't confuse ALS with conditions causing flaccid quadriparesis (like Guillain-Barré syndrome or acute spinal cord injury)
2. Overlooking Bulbar Symptoms: Even patients without obvious bulbar symptoms may have swallowing abnormalities detectable on videofluoroscopy 1
3. Missing Extra-motor Manifestations: Up to 50% of ALS patients have cognitive or behavioral changes, with 10-15% meeting criteria for frontotemporal dementia 5

In conclusion, ALS presents with a combination of upper and lower motor neuron signs resulting in spastic weakness, not flaccid quadriparesis, and does not involve sensory abnormalities.