Can Amyotrophic Lateral Sclerosis (ALS) be visualized on Magnetic Resonance Imaging (MRI)?

MRI Findings in Amyotrophic Lateral Sclerosis (ALS)

MRI can visualize characteristic changes in ALS, but it is primarily used to exclude other conditions rather than to confirm the diagnosis, as findings may be subtle, non-specific, or appear later in the disease course. 1

Key MRI Findings in ALS

Brain MRI Findings

• Corticospinal Tract Abnormalities:

  • Hyperintensity on T2/FLAIR sequences along the corticospinal tracts from subcortical white matter to pons, most commonly seen in the posterior limb of the internal capsule and cerebral peduncles 1, 2
  • Hyperintensity on T1-weighted images in patients with pronounced upper motor neuron signs (may reflect severe pathological changes) 3
  • These signal changes likely correspond to underlying demyelination, axonal degeneration, and gliosis 1

• Motor Cortex Changes:

  • Hypointensity in the motor cortex on T2*/SWI sequences 2
  • Selective motor cortex atrophy 2

Spinal Cord MRI Findings

• "Snake eyes" appearance - abnormal T2/STIR signal in the anterior horns 1
• Hyperintensity in the anterolateral column on T1-weighted images 3
• Hyperintensity in the lateral corticospinal tracts on T2-weighted images 3

Diagnostic Value

The simultaneous presence of corticospinal tract FLAIR hyperintensity and motor cortex SWI hypointensity offers the highest diagnostic accuracy:

• Sensitivity: 70%
• Specificity: 81%
• Positive predictive value: 90%
• Accuracy: 73% 2

However, these findings are:

1. Not always present, especially early in the disease
2. May be seen in normal individuals or other neurological conditions
3. Correlation with clinical upper motor neuron signs is inconsistent 3

Clinical Correlation

• MRI findings are more prevalent in definite-phase ALS (75%) compared to indefinite-phase ALS (22%) 4
• The combination of CST FLAIR hyperintensity and motor cortex SWI hypointensity is associated with shorter survival (HR: 6.56) 2
• Positive MRI findings correlate with average or rapid progression of the disease 5

Role in Clinical Practice

According to the ACR Appropriateness Criteria:

1. MRI head without IV contrast is usually appropriate for the initial imaging of patients with suspected motor neuron disease 1
2. MRI spine without IV contrast may be appropriate for certain patients with suspected motor neuron disease 1
3. The primary purpose of imaging in ALS is to exclude other conditions with similar clinical presentations rather than to confirm the diagnosis 1

Common Pitfalls and Caveats

• Relying solely on MRI for diagnosis - electromyography and nerve conduction studies remain key diagnostic tests for ALS 1
• Misinterpreting normal variants as pathological - CST hyperintensity can be seen in normal volunteers and other neurological conditions 3
• Failing to recognize that MRI findings may change with disease progression - in some cases, signal abnormalities may become less marked as the disease advances 3
• Not using appropriate sequences - T2*/SWI sequences are important for evaluating motor cortex involvement 2

Advanced MRI Techniques

While conventional MRI is most commonly used in clinical practice, advanced techniques may provide additional information:

• Diffusion tensor imaging (DTI)
• Spinal cord morphometry
• Inhomogeneous magnetization transfer (ihMTR)

However, these advanced techniques are primarily research tools and not yet part of routine clinical evaluation 6.