Differentials
Psoriasis
SIGNS / SYMPTOMS
May mimic or be indistinguishable from scalp SD to the extent that the term 'sebopsoriasis' is employed.
Nail pitting, intergluteal pinking (erythematous plaques of the intergluteal fold), arthralgia, and the extensor distribution of psoriatic plaques are characteristic features.
Actinic keratosis
SIGNS / SYMPTOMS
May appear as an erythematous papule with scale more firmly adherent than that of SD.
Palpated more easily than visualised and has a roughened quality on palpation.
INVESTIGATIONS
Skin biopsy shows proliferating atypical squamous cells.
Systemic lupus erythematosus (SLE)
SIGNS / SYMPTOMS
Sub-acute SLE may have similar clinical features.
SLE plaques are less scaly, carmine-coloured, and have a more firmly adherent scale.
INVESTIGATIONS
Skin biopsy shows perivascular cellular infiltrate. Direct and indirect immunofluorescence tests reveal immunoglobulin deposition.
Serum antinuclear antibody (ANA) and anti-extractable nuclear antigen (anti-ENA) may be positive.
Tinea capitis
SIGNS / SYMPTOMS
Scalp scaling with or without hair loss.[17]
Common in pre-adolescent children, unlike SD.
May not be inflammatory or erythematous.
Pre-adolescent children with apparent SD should be suspected of having tinea capitis.
INVESTIGATIONS
Potassium hydroxide preparation of scale for branching hyphae. Biopsy also shows hyphae. Culture is positive for Malassezia.
Histiocytosis X
SIGNS / SYMPTOMS
SD-type scaling with fine erythematous papules.
INVESTIGATIONS
Skin biopsy shows a dermis with S-100 positive histiocytes.
Rosacea
SIGNS / SYMPTOMS
Central facial erythema with papules and pustules.
INVESTIGATIONS
Skin biopsy does not show changes of SD.
May show granulomatous changes.
Dermatitis, atopic
SIGNS / SYMPTOMS
Erythema of face in infants, of antecubital fossae in older patients. History of atopy.
INVESTIGATIONS
Skin biopsy does not show changes of SD.
Has uniform epidermal spongiosis.
Leiner's disease
SIGNS / SYMPTOMS
Familial pattern.
Failure to thrive.
Recalcitrant diarrhoea.
Recurrent infection with gram-negative organisms.
Erythroderma is common.
Has been attributed to an inherited dysfunction or deficiency of complement C3 or C5.[18]
INVESTIGATIONS
The laboratory assay measures uptake of a particle that requires C5 for total opsonisation.[18] Phagocytic assays using such particles as erythrocytes, pneumococci, or latex particles are said to be inadequate screening procedures for C5 deficiency.
Impetigo
SIGNS / SYMPTOMS
Characteristic golden crusts typically seen on face.
May be secondary to other cutaneous disorders such as SD.
INVESTIGATIONS
No differentiating tests.
Dermatitis, contact
SIGNS / SYMPTOMS
Dermatitis at site of contact, often sharply demarcated.
Allergen may be cryptic.
INVESTIGATIONS
Patch testing may aid identification of the offending agent.
Acne vulgaris
SIGNS / SYMPTOMS
Facial erythema with comedonal formation, papules, and pustules.
INVESTIGATIONS
No differentiating tests.
Lichen planus
SIGNS / SYMPTOMS
Violaceous polygonal papules associated with oral leukoplakia.
INVESTIGATIONS
No differentiating tests.
Erythroderma
SIGNS / SYMPTOMS
Extensive, widespread erythema. May be due to a flare of SD but can also arise from pre-existing dermatoses, underlying lymphoma or other cancers, and drug eruptions, or it can be idiopathic.
INVESTIGATIONS
No differentiating tests.
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