The measurement of itch with sensitive limb movement meters.

A sensitive electromagnetic movement detector has been developed to estimate itch by measuring scratch during sleep. The cumulative time of nocturnal limb movements of patients with itchy and non-itchy liver diseases was estimated. Non-itchy patients moved their arms for 24 +/- 9.3 min/8 h (mean +/- s.d.) and their legs for 16 +/- 7.0 min/8 h. The limb movements were not related to left or right handedness or the sex or age of the patient. Itchy patients had increased nocturnal limb movements; however, the increase in arm movement (up to five times control level) was much greater than the increase in leg movement (up to twice control level). The marked increase in arm movements in itchy patients supports the view that this movement is largely due to scratching. The reproducibility of the estimates of arm movements was reasonable (within-person coefficient of variation 22%). In three studies, treatment resulted in a reduction of arm movements to normal levels. The measurement of cumulative nocturnal arm movement by these sensitive meters appears to be a valid estimate of scratch and superior to a subjective assessment of itch. The devices may also be applied to other studies, such as the effects of hypnotic drugs on sleep movement and the measurement of vibration.