An electrical stimulation lead includes a lead body electrodes disposed along the distal portion of the lead body or on a paddle body coupled to the lead body terminals disposed along the proximal portion of the lead body and conductors coupling the terminals to the electrodes. The lead also includes a conductor guide disposed within the lead body and extending from the proximal portion of the lead body. The conductor guide defines a central lumen and a plurality of conductor lumens disposed around the central lumen. The lead further includes a stiffening agent disposed within at least one of the conductor lumens. The stiffening agent includes a) a material formed from a granular particulate material, b) a polymeric material having a durometer at least 10% greater than the durometer of the conductor guide, or c) a continuous epoxy layer within which discrete epoxy particles are also disposed.
