Subacute combined degeneration (SCD) is a neurological disorder primarily caused by vitamin B12 deficiency. This condition leads to progressive demyelination and axonal damage, predominantly affecting the dorsal and lateral columns of the spinal cord. This review provides a comprehensive overview of SCD, detailing its complex etiology, pathophysiology, and clinical presentation. We highlight the critical role of magnetic resonance imaging (MRI) in the diagnostic process, discussing both the characteristic spinal cord findings and the more subtle intracranial abnormalities. Furthermore, we address the diagnostic challenges presented by conditions that mimic SCD in MRI, such as multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). We conclude by outlining current treatment pathways and identifying key areas for future research, including the use of advanced neuroimaging techniques and the potential for new therapeutic approaches. This updated synthesis aims to provide a clear framework for clinicians and researchers to better understand and manage SCD.