Can ALS be detected on an MRI?

Magnetic resonance imaging (MRI) is part of the diagnostic process for ALS. MRI of the brain and spinal cord is used to rule out rare conditions that can cause ALS-like symptoms. These differential diagnoses include, in particular, structural changes in the spinal cord that may be associated with motor symptoms, including muscle weakness and spasticity.

The degeneration of motor neurons in the brain and spinal cord characteristic of ALS cannot be detected by MRI. The neurodegeneration associated with ALS occurs at a cellular, microscopic level that is beyond the scope of MRI imaging. Only in a small proportion of ALS patients does an MRI of the brain show changes in the appearance of the pyramidal tract. These are nerve tracts that run from the motor neurons of the cerebral cortex through central structures of the brain (internal capsule; Capsula interna) to the spinal cord. These changes are detectable in fewer than 10% of all people with ALS. For the majority of ALS patients, MRI findings serve to rule out other conditions, and no direct signs of ALS are apparent.