The motor band sign is a radiological sign described in amyotrophic lateral sclerosis (ALS).
It refers to the appearance of the cortex on axial GRE and SWI MRI in patients with amyotrophic lateral sclerosis 1,2. On these sequences, and in the axial plane, curvilinear bands of low signal may be appreciated within the cortical gray matter, almost exclusively along the primary motor cortex (i.e. 'motor bands' of low signal) 1,2. Although this pattern of low signal is usually seen bilaterally, it has been reported to also occur unilaterally 2. Occasionally, T2/FLAIR sequences may also demonstrate the same low signal 1-4.
This sign is produced because of iron accumulation within microglia in the motor cortex 1. The mechanisms for this have not been fully elucidated, however it has been postulated that perhaps microglia accumulate this iron as they phagocytose degenerating neurons from the primary motor cortex 1.
It is important to note that this radiological sign is not specific for amyotrophic lateral sclerosis 1-4. Indeed, low T2/FLAIR/GRE/SWI signal in the precentral gyrus has been documented to also occur in patients with other neurological disorders (e.g. Parkinson disease, Alzheimer disease, spinocerebellar ataxia type 17) and even in many normal adults as an age-related phenomenon 1-5. This might be due to the fact that the motor cortex has the highest cortical concentration of iron 1.
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