CAESAR is an Italian multicenter retrospective cohort study on Rare Neuromuscular and Neurodegenerative diseases (RND), based on information available in regional administrative healthcare databases. The aims are 1) to describe the prescriptive patterns of drugs used for the treatment of patients affected by RND and identify patient characteristics associated to these patterns in the three Italian regions (Tuscany, Umbria, Lazio), accounting for over 10 million residents, and 2) to perform a comparative evaluation of the effectiveness and safety of drugs used for the treatment of RND, with a focus on specific active agents. The study population will be enrolled in the period 2009-2019, with a two-year look-back and at least 1 year of follow-up, including patients, resident in one of the three regions and affected by Amyotrophic lateral sclerosis (ALS), Progressive muscular atrophy (PMA), Pseudobulbar palsy, Progressive bulbar palsy (PBP), Primary lateral sclerosis (PLS), Other motor neuron disease, Myasthenia gravis (MG). Patients will be defined from Hospital discharge records (ICD-9-CM codes), disease specific copayment exemptions, and, as far as possible, disease specific drug treatments. Drug utilisation patterns will be based on drugs (ATC codes) prescribed to outpatients using the DDDs. Safety and effectiveness will be investigated using a new-user approach and applying both, intention-to-treat and as-treated analysis. Clinical data available in two of the participating regions for ALS patients will be used to 1) validate the algorithm used for patient identification, 2) validate the exposure definition, and 3) perform external adjustment. Data and analysis ill be managed through a common data model, with shared data scripts, performing the analysis at regional level (in-house) and pooling aggregated anonymous data to obtain overall results.