What are the diagnostic tests for Amyotrophic Lateral Sclerosis (ALS)?

Diagnostic Testing for Amyotrophic Lateral Sclerosis (ALS)

The diagnosis of ALS relies primarily on electromyography (EMG) and nerve conduction velocity studies, with imaging used mainly to exclude other conditions rather than confirm ALS. 1

Primary Diagnostic Tests

Electrodiagnostic Studies

• EMG and nerve conduction studies are the key diagnostic tests for ALS 1
  • Look for:
    • Evidence of active denervation (fibrillation potentials, positive sharp waves)
    • Chronic denervation/reinnervation (large motor units, reduced recruitment)
    • Fasciculations in multiple body regions
  • Must demonstrate both upper and lower motor neuron involvement
  • Should show abnormalities in multiple body regions

Clinical Examination

• Must demonstrate both:
  • Upper motor neuron signs: hyperreflexia, spasticity, Babinski sign
  • Lower motor neuron signs: weakness, atrophy, fasciculations
• Progression of symptoms over time is essential for diagnosis

Imaging Studies

MRI Brain and Spine

• MRI head without IV contrast is usually appropriate for initial imaging of patients with suspected motor neuron disease 1
• MRI spine without IV contrast may be appropriate for certain patients 1
• Primary purpose is to exclude other conditions with similar presentations
• Common MRI findings in ALS (though not diagnostic):
  • Abnormal T2/FLAIR signal in corticospinal tracts
  • "Snake eyes" appearance in anterior horns of the spinal cord 1

CT Imaging

• Not preferred due to limited soft-tissue characterization compared to MRI 1
• No role in making a positive diagnosis of ALS
• Limited utility in excluding other etiologies

Advanced Testing

Videofluoroscopy for Dysphagia Assessment

• Recommended at diagnosis for all ALS patients 1
• Can detect early signs of dysphagia even in patients without bulbar symptoms 1
• Evaluates both oral and pharyngeal phases of swallowing 1

Dysphagia Screening Tools

• EAT-10 questionnaire: high sensitivity (86%) and specificity (76%) for identifying aspiration risk 1
• Volume-Viscosity Swallow Test (V-VST): 92% sensitivity, 80% specificity 1
• Fiberoptic endoscopic evaluation of swallowing (FEES) can identify impaired chewing, tongue deficits, and pharyngeal residues 1

Diagnostic Algorithm

1. Initial clinical suspicion based on progressive weakness and both UMN and LMN signs
2. EMG and nerve conduction studies to confirm diagnosis
3. MRI brain and spine without contrast to exclude mimics
4. Videofluoroscopy for dysphagia assessment
5. Laboratory testing to exclude other conditions

Diagnostic Pitfalls

• Delay in diagnosis is common (average 12 months from symptom onset to diagnosis) 2
• Misdiagnosis often occurs due to:
  • Lack of knowledge about ALS among physicians 3
  • Failure to recognize early symptoms
  • Incomplete testing that misses either UMN or LMN signs
• ALS can initially present with restricted symptoms that may be confused with:
  • Progressive bulbar palsy (pure bulbar)
  • Progressive muscular atrophy (pure lower motor neuron)
  • Primary lateral sclerosis (pure upper motor neuron) 3

Emerging Diagnostic Approaches

• Neurofilament levels in CSF and/or serum provide Class II evidence supporting ALS diagnosis 2
• Genetic testing for familial ALS, particularly C9orf72 gene 4
• New Gold Coast Criteria may facilitate earlier diagnosis 2

Remember that early diagnosis is critical as it allows for:

• Earlier initiation of disease-modifying therapies
• Implementation of multidisciplinary care that improves survival
• Reduced psychological distress for patients 2
• Timely management of dysphagia and respiratory insufficiency