Motor Band Sign in Primary Lateral Sclerosis: A Case Report Proposing the Need for an Imaging Biomarker

Motor neuron disease is a degenerative condition involving both upper motor neurons (UMN) and lower motor neurons (LMN). While amyotrophic lateral sclerosis (ALS) is an overlap of upper and lower motor neuron involvement, primary lateral sclerosis (PLS) is predominantly an upper motor neuron involvement with lower motor involvement seen in the later stages of illness. Diagnostic criteria rely on clinical features and electrodiagnostic tests such as electromyography (EMG). EMG predominantly helps in determining lower motor neuron involvement. No definitive objective measures are currently available to determine upper motor neuron involvement. We describe a patient diagnosed with PLS based on consensus diagnostic criteria. The patient had absent LMN features both clinically and on EMG. Magnetic resonance imaging (MRI) was significant for hypointense signals in the bilateral motor strip area on susceptibility weighted sequence, suggesting a surrogate marker of degeneration involving motor neurons in the brain. Early recognition of this MRI pattern called motor band sign (MBS) can help determine the earlier diagnosis of this neurodegenerative condition, potentially translating to better treatment and outcome measures.