Diagnosis of scalp rashes

Author: Hon A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand, February 2016.


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
Pityriasis amiantacea

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
Tinea capitis

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
Scalp psoriasis

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
Seborrhoeic dermatitis of scalp

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
Atopic dermatitis of scalp

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
Discoid lupus erythematosus of scalp

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
Head lice

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
Scalp folliculitis

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 keloidalis nuchae

Folliculitis decalvans

Folliculitis decalvans:

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

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
Dissecting cellulitis

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
Erosive pustular dermatosis

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