Making a differential diagnosis

Several common skin conditions produce both rash and itching and may be mistaken for atopic eczema. Most can be differentiated from eczema on the basis of the type of rash, site of lesion or distribution.

Condition Rash Site(s) Distribution Other/key factors
Eczema9 Poorly demarcated Exudate/scaling Flexor surfaces of elbows and knees.

Face and neck

May affect trunk.

May become widespread

Often associated with asthma and rhinitis. A family history of eczema or atopy is common.
Allergic contact dermatitis9 Erythema, oedema and vesicles Usually on site of contact Site of contact

Previously sensitised sites may react to contact with allergen elsewhere on body

Allergy to leg ulcer treatments is a common cause of dermatitis on the leg
Irritant contact dermatitis9 Slight scaling and itching or extensive damage resembling a superficial burn Site of contact, often hands Site of contact

Sometimes a more diffuse eruption

Previous contact not required
Lichen simplex10 Very excoriated

May become heavily thickened

Neck, Forearm, Shins Either a localised patch or widespread Perpetuated by an 'itch-scratch' cycle
Lichen planus10 Flat topped, polygonal papular lesions

Shiny, mauve/red with white lines

Flexor surfaces of wrists and ankles

Shins, Palms, Oral muscosa

May be restricted to wrists and ankles or become very widespread May be intensely irritable
Discoid eczema10 Well demarcated. Round/oval lesions May arise almost anywhere Rare on the face Affects both children and adults
Pomphlyx10 Deep seated vesicles Sides of fingers

Palms, Soles of feet

Vesicles appear in 'crops' Early phases may manifest as a 'pricking' or 'tingling' sensation
Molluscum contagiosum9 White umbilicated papules Variable May vary from single solitary lesion to widespread eruption Mainly affects infants or young children
Drug reactions e.g. toxic erythema, Erythema multiforme9 Lesions occur in crops

May form 'target' lesions

Limbs, Trunk Localised or symmetrical Presents within days of starting drug therapy
Urticaria10 Raised wheals

Appear in crops

Anywhere on the body surface Individual wheals arise and disappear within a short time Can last for a few days at most

References:
  1. 9.Buxton PK (1998) ABC of Dermatology. 3rd edition. London, BMJ Publishing Group.
  2. 10.Graham-Brown R, Bourke J, Cunliffe T. Dermatology. Fundamentals of Practice. Mosby Elsevier, London 2008

Date of preparation: May 2009 / Code: E&D 09-002