Comezon

Dermatology anD general health

Itching

making a diagnosis in patients with itch is to determine whether
there is an underlying inflammatory skin disease causing the
itch or whether the itch is in the context of normal skin. Whilst
this appears straightforward, in practice it can be difficult as the
effects of scratching can make assessment of the skin difficult,
and rashes can beevanescent.6,7 The main points to consider in
the history and examination of itch are listed in Tables 1 and 2.
Many skin conditions cause pruritus, either localized or generalized, and these are covered in the relevant sections in these
issues.

Sue handfield-Jones

Dermatoses that are characterized by severe itch
Whilst many inflammatory dermatoses cause itch, some, for reasons unknown, causemore severe itch than others. These are:
• eczema of all types, including prurigo nodularis and lichen
simplex
• scabies
• lichen planus
• urticaria
• immunobullous disorders, including dermatitis herpetiformis
• Grover’s syndrome: this uncommon acantholytic dermatosis
usually affects older men and is often associated with sun exposure. The rash is very non-specific clinically but can bediagnosed
on skin biopsy.

Abstract
Itching, also known as pruritus, is the major symptom of skin disease
and is unique to skin and (less commonly) mucosae. It is a cause of
great distress to patients. the pathophysiology of itch is complex,
with a range of inflammatory mediators being implicated. Itch is not
a diagnosis and itchy patients always need careful evaluation. Itch can
beassociated with a rash or can occur on normal skin. Some rashes
such as lichen planus are characterized by severe pruritus. It is
important to detect signs of subtle inflammatory skin disease because a
patient presenting with generalized itch in the absence of any rash needs
to be investigated for underlying systemic causes. Systemic disease
associated with itch includes malignancy, bothhaematological and solid
tumours, renal, hepatic and thyroid dysfunction and infections. treatment of itch is difficult, with a range of topical, physical and systemic
treatments used.

Easily missed rashes
Key to the management of patients with pruritus is distinguishing
those who have rashes from those who do not. Some rashes are
easily missed, either because they cannot be distinguished fromscratch damage or because they are transient and may not be
visible when the patient is in clinic.
Dry skin – this is one of the most common causes of itch
but the clinical signs can be subtle or overlooked. Other terms
used include xerosis, winter itch, senile pruritus and asteatotic
eczema. The changes are most common on the lower legs. Exacerbating factors include age, low atmospherichumidity (centrally
heated houses in winter) and overuse of soap and detergents on
the skin, especially with hot water. Patients with hypothyroidism

Keywords dermatoses; itch; pruritus; rash

Definition and general information
Itch is the unpleasant sensation that leads to the desire to scratch
the skin. The terms ‘itch’ and ‘pruritus’ can be used interchangeably. Itch can be so severe that itcauses insomnia, and scratching
can be so intense that the skin is left raw and bleeding. Chronic
itch has a major impact on quality of life.1
Reproducible measurement of itch for research is difficult. Visual analogue scales can be used to give an indication
of itch severity. Scratching can be measured using movement
detectors.2
The pathophysiology of itch is still under investigation. Itchis caused by a complex interplay between chemical mediators
derived from both skin and blood with peripheral and central
neural mechanisms. Whilst histamine is the best known mediator of itch there are many others. The sensation of itch is transmitted via unmyelinated pain fibres and functional imaging of
the brain shows that multiple areas are involved in itching and
scratching.3–5...