Allocnesis

Allocnesis is an abnormal sensory condition in which a physiologically nonpruritogenic stimulus (such as a light touch of clothing) induces itching (Andersen HH et al. 2018). The increased pruritic reactivity of the skin to tactile stimuli is presumably decisive for pruritus in connection with insect bites, urticaria, xerosis cutis or atopic dermatitis.

In animal experiments, mechanical stimulation 0.7 cm from the injection site after intradermal injection of histamine in mice may induce discrete itching directed at the stimulus. This allogeneic, pruritic impulse starts 10 minutes after the intradermal histamine injection and reaches its peak 20-40 minutes after the injection site and then decreases over the next hour. Allocnesis can be suppressed by local anaesthetics and reduced by cooling.

The terms allocnesis or hyperknesis are comparable to the pain-associated dysesthesias allodynia and hyperalgesia.

1. Akiyama T et al (2012) Mouse Model of Touch-Evoked Itch (Alloknesis). Journal of Investigative Dermatology 132: 1886-1891

2. Andersen HH et al (2018) Alloknesis and hyperknesis-mechanisms, assessment methodology, and clinical implications
   of itch sensitization.Pain 159:1185-1197.