EVALUATION COMMITTEE

The Faculty Council has appointed the following adjudication committee to evaluate the thesis and the associated lecture: 

• Dr. Romina Nassini, Associate professor, University of Florence, Italy.
• Dr. Sara Invitto, Associate professor, University of Salento, Italy
• Dr. Romulus Lontis, HST, Aalborg University, Denmark (Chairman).

Moderator:
Prof. Lars Arendt-Nielsen, HST, Aalborg University

ABSTRACT

Itch is a sensation characterized by the innate desire to scratch. Although acute itch is generally tolerable, chronic itch (itch occurring for more than 6 weeks) can severely affect the patients’ quality of life and have a prevalence up to 25%. In the last decades, many therapies and treatments have been developed, but to date, their efficacies are scarce and may present with side effects. If efficient non-pharmacological treatment options could be developed this would have a major clinical potential.
Scratching itchy skin is ultimately a form of self-inflicted mechanical pain that can help in relieving itch to some extent. Therefore, many studies have focused on the interaction between itch and pain.
Regarding heat stimulations, it has been shown that long noxious heat stimuli can inhibit itch, but on the other hand, such stimuli may cause hyperalgesia and skin damage.
Many clinical observations indicate that patients can experience increased itch in warm environments, suggesting some relationships between heat and itch sensations.
A 70 years old study showed that a paradoxical itch sensation could be achieved when anaesthetised skin was stimulated with what was defined as a “burning” sensation.
Taken together these independent observations, seem to indicate that thermal perception may have a role in modulating different aspects of itch sensation, and therefore it is of interest to understand better the mechanism underlining these modulatory effects.
Within this context, this PhD project aimed at investing these aspects: 1) the effects of very short heat stimuli (ranging from innocuous to noxious) on various itch modalities; 2) how continuous skin warming affects itch intensity in human surrogate itch models; 3) investigate and possibly confirm with a more modern and systematic approach the observed dysesthesia of paradoxical itch sensation when a “burning” stimulus is applied on top of anaesthetised skin.
The first study showed that homotopical transient noxious heat stimuli were able to inhibit histaminergic itch and, to a lesser extent, non-histaminergic itch induced by cowhage. When the stimuli were applied heterotopically there was no significant inhibition suggesting that, at least for very transient stimuli, the observed inhibitory effect relies on peripheral mechanisms.
The second study showed that mild skin heating selectively aggravates serotoninergic and histaminergic itch but not cowhage-induced itch. These results partially agree with what is observed in animals (increased serotoninergic itch intensity) and parts are in direct contrast with them (unchanged histaminergic itch intensity).
The third study failed to confirm a 70 years old observation. Applying a heat ramp (ranging from warm to noxious heat) on anaesthetised skin did not evoke a paradoxical itch sensation at any of the time points analysed.
In conclusion, this dissertation unveils a potential role of thermal stimulation to modulate itch. Further studies are needed to investigate this in a clinical context.