Neuroimaging in amyotrophic lateral sclerosis

Several neuroimaging modalities have been used with varying success to aid the clinical process of establishing the diagnosis of amyotrophic lateral sclerosis (ALS). By demonstrating evidence of occult upper motor neuron degeneration in vivo, a speedier and more definitive diagnosis in suspected cases could lead to earlier treatment and earlier enrollment in clinical trials. Findings compatible with ALS on routine MRI are not consistently found and are non-specific. Thus, routine anatomic imaging is useful in ruling out diseases that mimic ALS, but not in classification of new cases. Functional imaging techniques, such as PET and fMRI, have provided fascinating insights into the cortical functional reorganization that accompanies muscular weakness. PET and SPECT have revealed involvement of regions of the brain beyond the motor cortex, something not well appreciated by pathological examination. Of great need is a surrogate marker of therapeutic efficacy to make drug evaluation more efficient; neuroimaging, and magnetic resonance spectroscopy in particular, holds great promise in this regard in addition to helping us better understand the pathophysiological mechanisms of neurodegeneration.