The Aim of the Study is to Characterize Patients Exhibiting Muscular Atrophy and Weakness Who Require a Muscle Biopsy for Diagnosis (IBM vs Atypical MND), Through an Innovative Technique Which Enables the Evaluation of the Neuromuscular Junction Involvement in Each Condition

To achieve a diagnostic sensitivity of >90% for the differential diagnosis between IBM and MND integrating clinical variables (site of onset, scales reflecting disease progression rate, muscle strength), neurophysiological indices (presence and degree of active denervation signs, presence of myopathic or neurogenic motor unit potentials), histopathological parameters (myopathic or neuropathic pattern of disease) and metabolic measures (hyper- vs hypo-metabolism) into a multivariable binary logistic regression model, using the final diagnosis confirmed during longitudinal follow-up as the reference standard.

To investigate disease-specific histological signatures, comparing the pattern of fiber degeneration, the presence of inflammatory infiltrates, the presence of protein aggregation markers (such as pTDP-43) and their localization, the presence of mitochondrial changes (the percentage of age-exceeding number of COX-negative fibers) and the NMJ involvement by evaluating the presynaptic and postsynaptic integrity (quantified as the percentage of synaptophysin and Ach-R clustering, respectively) between IBM and MND (through Fisher's exact test or Mann-Whitney U test, as appropriate) and to evaluate the prognostic role of each histological parameter (through Kaplan-Meier followed by log-rank test and Cox proportional hazards regression).