From Amputation to Persistent Pain: A Review of Molecular and Cellular Processes in Phantom Limb Pain.

Phantom limb pain (PLP) is a frequent and often persistent consequence of limb amputation, characterized by pain perceived in the absent limb. Despite decades of research, its biological basis remains incompletely understood, and available treatments often provide inconsistent relief. This reflects the complex and heterogeneous nature of phantom limb pain, which cannot be explained by a single anatomical site or pathological process. Current evidence suggests that phantom limb pain emerges from the interaction of changes occurring at multiple levels of the nervous system. Peripheral nerve injury associated with amputation induces molecular and cellular alterations that may influence early nociceptive signaling. These changes can interact with adaptive and maladaptive responses within the spinal cord, including altered synaptic transmission and neuron-glia interactions, which may facilitate sustained amplification of pain-related signals. At supraspinal levels, long-term adaptations within distributed neural networks involved in sensory, motor, and affective processing may contribute to the persistence of pain perceptions in the absence of ongoing peripheral input. Immune-related signaling and long-term regulation of gene expression further modulate these processes and may contribute to inter-individual variability. In this narrative review, we synthesize current experimental and clinical evidence addressing the molecular and cellular processes associated with phantom limb pain following lower limb amputation. Findings are integrated across peripheral, spinal, and supraspinal levels, with consideration of immune-related and regulatory influences. By highlighting areas of convergence, uncertainty, and existing knowledge gaps, this review aims to provide a coherent biological framework that may support future experimental and translational research in this challenging field.