Diagnosis of scalp rashes

Introduction

Patients may present with a skin problem they believe to be confined to the scalp. A full medical and focussed cutaneous history should be followed by brief examination of relevant sites.

The most common scalp symptoms are:

• Itch
• Soreness
• Scale/flaking
• Pustules/sores

Itch may be associated with the majority of skin conditions in the scalp. Soreness is less frequent.

Chronic scaly scalp disorders

Pityriasis amiantacea

Pityriasis amiantacea:

• Very thick asbestos-like scale
• Scale is very adherent to hair shafts
• Subsequent diagnosis usually seborrhoeic dermatitis or psoriasis

Tinea capitis

Tinea capitis:

• Irregular scaly plaques with moth-eaten hair loss
• May have inflammatory, abscess-like kerion
• Hairs are easy to extract
• Positive microscopy and culture of scrapings and extracted hair
• Sometimes, fluorescence on Wood light examination

Psoriasis

Scalp psoriasis:

• Any age, most > 15 years
• May be localised or diffuse
• May be isolated to scalp or involve other body sites
• Check ears, elbows, knees, nails
• Circumscribed erythematous scaly plaques
• Large, usually white scale
• Poor response to topical therapy (various shampoos, calcipotriol, potent topical steroids)
• Hair loss uncommon, but when occurs, loose hair shafts can be extracted from scaly plaques

Seborrhoeic dermatitis

Seborrhoeic dermatitis:

• Infants or > 13 years
• May be localised or diffuse
• May be isolated to scalp or involve other body sites
• Check ears, eyebrows, nasolabial folds
• Thin salmon-pink flaky plaques, sometimes annular
• Small flakes of yellow or white scale
• Good, temporary, response to topical therapy (ketoconazole shampoo, mild topical steroid)
• Hair loss uncommon, but when occurs, loose hair shafts can be extracted from secondarily infected, oozy plaques

Atopic dermatitis

Atopic dermatitis:

• Any age especially children
  • In infants, may overlap with seborrhoeic dermatitis
• Usually diffuse and very itchy
• Involves other body sites
  • Scalp rash rarely prominent
  • Check elbow flexures, popliteal fossae, eyelids
• Ill-defined erythematous blistered or dry plaques
• Lichenification
• Dryness rather than loose scale
• Good response to properly applied topical therapy (potent topical steroid)
• Hair loss rare

Discoid lupus erythematosus

Discoid lupus erythematosus:

• Localised erythematous, scaly and hairless, scarred plaques; often multiple
• May be isolated to scalp or involve other body sites
• Check nose, cheeks, ear concha
• Lichen planopilaris
• Localised, sometimes erythematous bald plaques
• Perifollicular scale
• Lonely hairs

Chronic pustules and erosions

Head lice

Head lice:

• Usually, but not always, young child
• Look for lice on the nape of neck and behind ears
• Nits are adherent white grains on hair shafts
• Red-brown spots on the skin are due to excreted digested blood.
• Excoriations, hair pulled out

Dermatitis herpetiformis

Dermatitis herpetiformis:

• Scalp a common site, also shoulders, buttocks elbows, knees
• Intensely itchy solitary or multiple blisters, rarely seen, as scratched

Scalp folliculitis

Scalp folliculitis:

• Itchy or painful follicular pustules and scratched erosions
• No hair loss
• Poor response to topical steroid
• May improve with long-term oral tetracycline

Folliculitis keloidalis nuchae

Folliculitis keloidalis nuchae:

• Males with dark coarse hair
• Occipital scalp
• Few pustules
• Firm follicular papules
• Larger keloid scars with sparse hairs

Folliculitis decalvans

Folliculitis decalvans:

• Itchy or painful follicular pustules, perifollicular crusting
• Irregular bald, scarred areas; usually solitary
• May improve with long-term oral tetracycline

Dissecting cellulitis

Dissecting cellulitis:

• Also known as perifolliculitis capitis abscedens et suffodiens
• Associated with acne conglobata, hidradenitis suppurativa
• Crusting, inflammatory nodules, large fluctuant cysts, with hair loss

Erosive pustular dermatosis

Erosive pustular dermatosis:

• Elderly, sun damaged, bald or very thin hair
• One or more masses of greenish pus
• There may be underlying keratotic plaques
• Arise within actinic keratoses or squamous cell carcinoma