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 and perinium. | Either widespread or a localised patch. | Perpetuated by an 'itch-scratch' cycle. |
| Lichen planus10 | Flat topped, polygonal papular lesions, shiny, mauve/red with white surrounding lines. |
Flexor surfaces of wrists and ankles. Shins and palms. Oral muscosa. |
May be restricted to wrists and ankles or become very widespread. | May be intensely irritable. |
| Discoid eczema10,11 | 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 and 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 and trunk. | Localised or symmetrical. | Presents within days of starting drug therapy. |
| Urticaria10 | Raised wheals, can 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:
- 9.Buxton PK (1998) ABC of Dermatology. 3rd edition. London, BMJ Publishing Group
- 10.Graham-Brown R, Bourke J, Cunliffe T. Dermatology. Fundamentals of Practice. Mosby Elsevier, London 2008
- 11.Graham-Brown R, Burns T. Lecture Notes. Dermatology. 9th Edition. 2007