What are the early signs of amyotrophic lateral sclerosis (ALS)?

Early Signs of Amyotrophic Lateral Sclerosis (ALS)

The earliest signs of ALS typically manifest as asymmetric muscle weakness in the limbs (difficulty with hand dexterity or gait abnormalities) or bulbar symptoms (difficulty speaking or swallowing), accompanied by muscle fasciculations, atrophy, and hyperreflexia. 1, 2, 3

Initial Presentation Patterns

ALS presents in two primary forms that determine the initial symptom pattern:

Limb-Onset ALS (Most Common)

• Asymmetric weakness in hands or feet causing problems with dexterity (difficulty buttoning clothes, writing, or using utensils) or gait disturbances (foot drop, tripping, stumbling) 3, 4
• Muscle fasciculations (visible twitching under the skin) in affected limbs 2, 3
• Muscle atrophy (wasting) that becomes progressively noticeable 3, 4
• Hyperreflexia (abnormally brisk reflexes) despite muscle weakness—a hallmark combination 1, 2

Bulbar-Onset ALS (20-30% of Cases)

• Dysarthria (slurred or difficult speech) as the initial symptom 5, 3
• Dysphagia (difficulty swallowing) that may be subtle initially 5, 3
• Tongue fasciculations and atrophy 4
• Bulbar-onset carries a shorter life expectancy compared to limb-onset 6

Critical Distinguishing Features (Upper + Lower Motor Neuron Signs)

The diagnosis requires both upper and lower motor neuron involvement—this combination distinguishes ALS from mimics 1, 2:

Lower Motor Neuron Signs

• Muscle fasciculations (spontaneous twitching) 2, 3
• Muscle weakness and atrophy 2, 3
• Decreased muscle tone in affected areas 2

Upper Motor Neuron Signs

• Hyperreflexia (exaggerated reflexes) 1, 2
• Spasticity (increased muscle tone/stiffness) 1, 2
• Pathological reflexes (Babinski sign) 1

Progressive Spread Pattern

• Symptoms spread contiguously from one body region to adjacent regions over months 1, 2
• The disease does not present with sudden onset or remain static—progressive worsening is essential for diagnosis 1, 3
• Weakness becomes bilateral and global over time, though initially asymmetric 4

Critical "Red Flag" Symptoms

These features should prompt immediate neurological evaluation 4:

• Weakness without any sensory symptoms (numbness, tingling, pain)—ALS spares sensory function 3, 4
• Profound weakness and atrophy in multiple nerve distributions that don't follow a single nerve pattern 4
• Progressively bilateral symptoms spreading to involve both sides of the body 4
• Presence of bulbar symptoms (tongue fasciculations, speech/swallowing difficulties) alongside limb symptoms 4

Preserved Functions (Important Negatives)

These functions remain intact in ALS and their impairment suggests an alternative diagnosis 3:

• Sphincter control (bowel and bladder function) remains normal 3
• Sensory function is completely preserved—no numbness or sensory loss 3, 4
• Intellectual abilities and cognition are preserved (though frontotemporal dementia can co-occur in some cases) 3
• Eye movements typically remain intact 3
• Skin integrity is maintained 3

Common Diagnostic Pitfalls

Early ALS is frequently misdiagnosed, particularly as compressive neuropathies 4, 7:

• 11% of hand surgeons have performed carpal or cubital tunnel surgery on patients later diagnosed with ALS 4
• Patients presenting with only upper motor neuron signs or only lower motor neuron signs early in disease are particularly challenging 7
• The combination of weakness with hyperreflexia (rather than the expected hyporeflexia seen in nerve compression) should raise suspicion 1, 2
• Failure to improve after nerve decompression surgery is a critical red flag 4

Timeline and Progression

• Initial symptoms develop over months, not days or weeks 3
• Patients develop severe, progressive muscular weakness over months to years 3
• Complete disability typically occurs within 2-5 years, often requiring ventilatory support and gastrostomy 3, 8
• Death usually occurs within 5 years of diagnosis, attributed to respiratory failure 3, 8