Secondary hyperalgesia is a phenomenon that refers to sensitization that occurs within the
central nervous system9. Repeated recruitment of C-fibers following an injury will produce
central sensitization by changing the respose properties of the membranes of secondary
neurons. This will result in an increase of the firing rate, a phenomenon known as windup10.
The high frequency recruitment of C fibers, either by increased repetitive stimuli or by a tonic
stimulation11, will induce an increase of the perceived pain, even if the intensity of the
stimulation remains constant. The spinal sensitization can persist for minutes, but can also be
present for hours and even days12. The prolonged activation of the NMDA receptors will
induce the transcription of rapidly expressed genes (c-fos, c-jun), resulting in sensitization of
nociceptors. This neuronal plasticity of the secondary neuron will result in a reduced threshold
in the spinal cord, producing hyperalgesic and allodynic responses that may persist even after
the healing of the injury. Considering the impact of sensitization, an aggressive and early
treatment plan to reduce pain will help in preventing ongoing chronic pain6.