Features Seen in Amyotrophic Lateral Sclerosis (ALS)
Flaccid quadriparesis is a characteristic feature of ALS, resulting from the combined degeneration of upper and lower motor neurons without sensory involvement.
Pathophysiological Features of ALS
ALS is characterized by the progressive degeneration of both upper motor neurons (UMN) in the motor cortex and lower motor neurons (LMN) in the brainstem and spinal cord 1. This combined loss leads to a distinctive clinical presentation with features of both UMN and LMN dysfunction:
Upper Motor Neuron Signs
- Hypertonicity/spasticity
- Hyperreflexia
- Positive Babinski sign
- Weakness with proximal predominance in lower limbs 1
Lower Motor Neuron Signs
- Hypotonia
- Hyporeflexia or areflexia
- Muscle fasciculations
- Muscle atrophy
- Weakness with characteristic patterns
- Muscle cramps 1, 2
Key Diagnostic Features
What ALS Does Include:
- Combined UMN and LMN signs
- Progressive muscle weakness and wasting
- Fasciculations in multiple body regions
- Flaccid quadriparesis as the disease advances 2
What ALS Does NOT Include:
- Sensory abnormalities - The disease process specifically spares sensory neurons 2
- Autonomic dysfunction
- Oculomotor neuron involvement 2
Imaging Findings
MRI is the recommended imaging modality for suspected motor neuron disease 3:
- Abnormal T2/FLAIR signal in corticospinal tracts from subcortical white matter to pons
- "Snake eyes" appearance in anterior horns of the spinal cord
- T2*-weighted or susceptibility-weighted imaging may show abnormal hypointensity in the precentral gyrus 3
Diagnostic Approach
The diagnosis of ALS is primarily clinical and requires:
- Evidence of both UMN and LMN degeneration
- Progressive spread of symptoms to different body regions
- Absence of sensory abnormalities
- Exclusion of other conditions that might mimic ALS 4
Clinical Course
- ALS typically has a focal onset but subsequently spreads to different body regions
- Median survival is approximately 2-5 years from symptom onset
- Respiratory muscle failure is the typical cause of death 4
- The diagnostic delay from symptom onset to definitive diagnosis averages 12 months 5
Important Considerations
- Up to 50% of ALS patients may develop extra-motor manifestations such as behavioral changes, executive dysfunction, and language problems 4
- In 10-15% of patients, cognitive problems are severe enough to meet criteria for frontotemporal dementia 4
- Early diagnosis is crucial as early initiation of therapy and multidisciplinary care results in cost savings and prolonged survival 5
The absence of sensory abnormalities is a key distinguishing feature of ALS, helping to differentiate it from other neurological conditions that may present with weakness but typically include sensory involvement.