What are the physical examination findings in amyotrophic lateral sclerosis (ALS)?

Physical Examination Findings in Amyotrophic Lateral Sclerosis

The physical examination in ALS reveals a characteristic combination of upper motor neuron signs (hyperreflexia, spasticity, hypertonicity) and lower motor neuron signs (muscle weakness, atrophy, fasciculations, flaccidity) occurring simultaneously in the same body regions, which is the diagnostic hallmark of this disease 1, 2.

Core Motor Neuron Findings

Upper Motor Neuron Signs

• Hyperreflexia in affected limbs and jaw
• Spasticity and increased muscle tone
• Pathological reflexes may be present (though not always)
• Pseudobulbar signs in bulbar-onset disease

Lower Motor Neuron Signs

• Progressive muscle weakness starting focally and spreading contiguously
• Muscle atrophy in affected regions
• Fasciculations (visible muscle twitching) - a key diagnostic feature
• Flaccidity in severely affected muscles

The simultaneous presence of both upper and lower motor neuron dysfunction in the same anatomical region distinguishes ALS from other conditions like cervical spondylotic amyotrophy 2, 3.

Distribution Patterns by Onset Type

Limb-Onset ALS (65% of cases)

• Hand weakness or foot drop as initial presentation
• Weakness spreads to contiguous muscle segments over time
• Typically asymmetric at onset
• Scapular and proximal/distal upper extremity involvement common 1, 4

Bulbar-Onset ALS (20-25% of cases)

• Dysarthria (speech difficulties)
• Dysphagia (swallowing problems)
• Tongue weakness and atrophy
• Impaired lip closure with drooling
• Weak masticatory muscles
• Reduced soft palate elevation 5, 1

Axial-Onset ALS (5-10% of cases)

• Bent posture from axial muscle weakness
• Early truncal instability 1

Associated Parkinsonian Features

Parkinsonism occurs in 25-80% of ALS patients and should be actively assessed 6:

• Bradykinesia/akinesia (most common)
• Parkinsonian gait and posture
• Rigidity (asymmetric rigidity suggests corticobasal syndrome)
• Tremor (less common than other parkinsonian features)
• Vertical gaze palsy or slowed downward saccades (suggests progressive supranuclear palsy overlap)
• Postural instability

Consistently Preserved Functions

Critical negative findings that help confirm ALS diagnosis:

• Cognition typically preserved (though 20-50% develop frontotemporal dementia) 5
• Extraocular muscles spared (except in PSP-ALS overlap)
• Urinary sphincters intact 2
• Sensory examination normal - no sensory deficits 4

Bulbar Examination Specifics

When bulbar symptoms are present 5:

• Impaired laryngeal elevation
• Reduced anterior hyoid excursion
• Decreased tongue base retraction
• Impaired bolus preparation and mastication
• Delayed initiation of pharyngeal swallow

When bulbar symptoms are absent, these functions remain preserved, but bolus transport abnormalities may still be present 5.

Respiratory Examination

• Assess for respiratory muscle weakness (late manifestation but critical)
• Evaluate work of breathing
• Note that respiratory failure is a primary cause of death 5

Key Examination Pitfalls

1. Early disease may show only lower motor neuron signs - upper motor neuron signs may be subtle or absent initially
2. Normal MMSE does not exclude ALS - cognitive screening is often normal in early stages 6
3. Absence of obvious pyramidal signs does not rule out upper motor neuron involvement - advanced techniques like MEP or brain MRI may be needed 4, 7
4. Fasciculations alone are not diagnostic - must be accompanied by weakness and other motor neuron signs

Examination Algorithm

1. Document muscle strength systematically in all four limbs, bulbar muscles, and respiratory muscles
2. Test reflexes comprehensively including jaw jerk, upper and lower extremity reflexes
3. Observe for fasciculations in multiple muscle groups (allow adequate observation time)
4. Assess tone for spasticity versus flaccidity
5. Perform cranial nerve examination focusing on bulbar function (tongue, palate, facial strength)
6. Test eye movements for vertical gaze abnormalities
7. Evaluate for parkinsonian features (gait, bradykinesia, rigidity)
8. Confirm sensory examination is normal
9. Document preserved sphincter function

The examination should reveal both upper and lower motor neuron signs in at least two body regions to support the diagnosis according to revised El Escorial criteria 7.