Regional glucose hypometabolic spread within the primary motor cortex is associated with amyotrophic lateral...

Here we investigate the process of neurodegeneration in amyotrophic lateral sclerosis (ALS). The relationship between the cortical field spreading of glucose metabolic decreases in the primary motor cortex (PMC) and the progression of corresponding extremity dysfunction was evaluated using [¹⁸F] fluoro-deoxyglucose (FDG)-positron emission tomography (PET).

Patients with ALS underwent [¹⁸F] FDG-PET and the resulting datasets were individually contrasted against healthy controls using the NEUROSTAT software. The extent ratio was defined as the proportion of pixels with a significant Z-score decrease within regions of the primary motor cortex (precentral gyrus or paracentral lobule) opposite to the impaired upper extremities (UEs) or lower extremities (LEs), respectively. Clinical symptoms in all extremities were assessed using an upper motor neuron (UMN) score and the MRC (Medical Research Council) sum score upon physical examination. Cross-sectional correlations were analysed between clinical symptoms, the duration of these symptoms, and the extent ratio.

Nineteen regions of the primary motor cortex corresponding to symptomatic limb in 10 participants were evaluated. In the corresponding region of the primary motor cortex, the extent ratio increased (same meaning as hypometabolic area spread) in association with symptom duration (r_s = 0.5, p = 0.03). Neither UMN nor lower motor neuron (LMN) scores were correlated with symptom duration. Three out of 19 impaired regions did not show upper motor neuron (UMN) signs upon physical examination. The extent ratio and UMN score-controlled symptom duration were partially correlated (r_s = 0.5, p = 0.05).

In patients with ALS, glucose metabolism decreased in the impaired side of the primary motor cortex depending on the clinical symptom progression in the corresponding extremities, regardless of the presence of clinical UMN signs. A decrement in glucose metabolism on FDG-PET corresponding to symptoms in the primary motor cortex might be an indicator of the time-dependent course of ALS neurodegeneration.