Primary and Secondary Hyperalgesia

Definition

Hyperalgesia means increased sensitivity to painful or to normally non-painful stimulation. There are two definitions of “primary” and “secondary” hyperalgesia. (1) According to one definition, a hyperalgesia is primary if it occurs in an inflamed body area or – in mononeuropathies – in the innervation territory of a lesioned nerve. Secondary are hyperalgesias occurring outside such an area. (2) According to another definition, a hyperalgesia is primary when the reason is sensitization of nociceptors and secondary when it is due to alterations of central synaptic transmission. For practical reasons, the first type of definition should be preferred, since it is purely descriptive.

In the case of inflammatory pain, primary hyperalgesia is usually due to sensitization of the primary afferent nociceptors. However, altered central nervous synaptic transmission may contribute. There are several forms of primary hyperalgesia: to tonic pressure (pressure hyperalgesia), to pin prick...