For personal use. Only reproduce with permission from The Lancet Publishing Group.
• Vol 361 • February 22, 2003 • www.thelancet.com
Itch, along with pain, is a major part of nociception and
an important symptom of systemic problems, as well as
neuropathophysiology and molecular basis has been
investigational methodology in man, and unsuitability of
animal models. Since the last update in
than 5 years ago on itch pathophysiology,
begun to overcome these difficulties, with important
Definitions, types, and clinical classification
Itch has many similarities to pain.
Both are unpleasant
patterns differ—pain elicits a reflex withdrawal, whereas
itch leads to a scratch reflex. However, both can lead to
serious impairment of quality of life.
first, a well localised itch at the site of the
stimulus, which persists only briefly after the stimulus
has been removed; and second, a subsequent diffuse
responds with intense itch when exposed to gentle touch
or other minor stimuli. This sensation of itchy skin is
also called alloknesis.
has proposed a clinical classification of four
understanding of the peripheral and central origins of
Itch originating in the skin, due to inflammation,
dryness, or other skin damage, is termed pruritoceptive
and is transmitted by C nerve fibres. Examples are itch
due to scabies, urticaria, and reactions to insect bite.
Department of Dermatology, Wake Forest University, Winston
Salem, North Carolina, USA
(Prof G Yosipovitch
; Department of
Dermatology, Faculty of Medicine, Hospital University Kebangsaan
Malaysia, Kuala Lumpur, Malaysia
(Prof M W Greaves
Department of Anaesthesiology, Mannheim University, Heidelberg,
Prof Gil Yosipovitch, Department of
Dermatology, Wake Forest University, Medical Center Boulevard,
Winston Salem, NC 27517, USA
Itch that arises because of disease located at any point along
the afferent pathway is called neuropathic itch.
zoster neuropathy and the itch occasionally associated with
multiple sclerosis and brain tumours are in this category.
Neurogenic itch is defined as that which originates centrally
but without evidence of neural pathology, such as the itch
of cholestasis, which is due to the action of opioid
neuropeptides on µ-opioid receptors.