Hyperalgesis vs. Allodynia

It is important in reading the literature to bear in mind that hyperalgesia and allodynia are different.


Hyperalgesia is increased pain from PAINFUL stimulus, Mechanical (touch) hyperalgesia is evaluated with various tests, such as the Randall-Selitto test. John Bonica and others termed this “hyperpathia”. However, Willia and others prefer the “hyperalgesia” term.

Allodynia is pain from NONPAINFUL stimulus (or, less commonly, pain in an area not specifically involved in the painful stimulus). Mechanical allodynia is typically tested with fine filaments (Von Frey hairs).

In Sept. 2004 Pain, Chacur et al demonstrate the rather surprising finding that the pathways for hyperalgesia and allodynia respond to different components of snake venom. Using snake venom, Chacur showed that inactive Lys49 venom caused hyperalgesia but only active Asp49 venom caused allodynia. These two components of Bothrops snake venom are differ in variety of amino acid at the location indicated, and this difference controls whether or not the venom is catalytically active, and which type of pain phenomenon is linked.

The difference in pain pathways is very significant. We certainly look forward to learning more about how these components feed into pain mechanisms and hope that labelling studies will reveal more about the differences between hyperalgesia and allodynia.

In the meantime, it is important to let your clinicans know WHICH symptomx you have. To do this, you must commit to understanding the terms of pain description. Elsewhere at this site, we have pointed out that some with CP have thermal allodynia and some do not.

We have also cited studies showing DNA impairment is part of nerve injury pain and that CP involves NMDA increase, which interferes with DNA precursor formation. (See Neuropathic touch not the same as thermal allodynia). This new study may reveal further information about the mechanisms of pain.