Scalp Dermatoses: Overview of Common Conditions
Scalp dermatoses encompass a spectrum of infectious, inflammatory, and parasitic conditions that share overlapping clinical features including scaling, erythema, pruritus, and hair loss, making accurate diagnosis essential for appropriate management 1, 2, 3.
Common Scalp Dermatoses
Tinea Capitis (Scalp Ringworm)
Tinea capitis is a dermatophyte infection of scalp hair follicles and surrounding skin, predominantly affecting prepubertal children, requiring systemic antifungal therapy for cure 1.
Clinical Presentations
Noninflammatory patterns:
Grey patch: Microsporum infections produce fine scaling with patchy circular alopecia appearing dull grey due to arthrospores coating affected hairs. Anthropophilic species (M. audouinii, M. ferrugineum) cause minimal inflammation, while zoophilic species (M. canis, M. gypseum) trigger more intense responses 1.
Black dot: Trichophyton species (T. tonsurans, T. violaceum, T. soudanense) create relatively non-inflammatory alopecic patches with fine scale, studded with broken-off swollen hair stubs appearing as "black dots." In the U.K., T. tonsurans accounts for 50-90% of cases 1.
Diffuse scale: Presents as generalized scalp scaling resembling dandruff, with minimal or absent alopecia 1.
Inflammatory patterns:
Diffuse pustular: Patchy alopecia coexists with scattered pustules or low-grade folliculitis, often with painful regional lymphadenopathy 1.
Kerion: A painful, boggy inflammatory mass with associated alopecia, studded with pustules and matted with thick crust. This represents a delayed host inflammatory response and is commonly misdiagnosed as bacterial abscess. Regional lymphadenopathy is typical 1.
Favus: Chronic inflammatory variant (T. schoenleinii) characterized by yellow, crusted, cup-shaped lesions ("scutula") around follicular openings, potentially resulting in cicatricial alopecia 1.
Diagnosis
Obtain scalp specimens via scalpel scraping, hair pluck, brush, or swab for microscopy and culture before initiating treatment 1. However, when kerion is present or cardinal signs exist (scale, lymphadenopathy, alopecia), commence treatment while awaiting mycology results 1.
Treatment Algorithm
Topical therapy alone is inadequate—oral antifungal therapy is required for clinical and mycological cure 1.
Treatment selection depends on the causative organism:
For Trichophyton species (T. tonsurans, T. violaceum, T. soudanense):
- First-line: Terbinafine 1
- <20 kg: 62.5 mg daily for 2-4 weeks
- 20-40 kg: 125 mg daily for 2-4 weeks
40 kg: 250 mg daily for 2-4 weeks
For Microsporum species (M. canis, M. audouinii):
- First-line: Griseofulvin 1
- <50 kg: 15-20 mg/kg/day for 6-8 weeks
50 kg: 1 g daily for 6-8 weeks
Rationale: Terbinafine is fungicidal with superior efficacy against Trichophyton but fails against Microsporum because it cannot be incorporated into prepubertal children's hair shafts or reach scalp surface arthroconidia 1. Conversely, griseofulvin demonstrates significantly better efficacy for Microsporum infections (8 weeks griseofulvin superior to 4 weeks terbinafine) 1.
Treatment failure management:
- Consider non-compliance, suboptimal absorption, organism insensitivity, or reinfection
- If clinical improvement with positive mycology: continue current therapy 2-4 weeks
- If no clinical improvement: switch to second-line therapy (itraconazole 5 mg/kg/day) 1
Critical pitfall: A pruritic papular "id" eruption (dermatophytid) may appear during treatment initiation, representing cell-mediated host response—do not discontinue antifungal therapy; treat symptomatically with topical corticosteroids 1.
Seborrheic Dermatitis
Seborrheic dermatitis presents as symmetric, poorly defined erythematous patches with yellow, oily scales and fine superficial desquamation in sebaceous-rich areas 4. In darker skin, erythema may be subtle with hypopigmented, slightly scaly areas as the presenting sign 4.
Treatment
Scalp seborrheic dermatitis:
- First-line: Topical antifungal shampoos (ketoconazole, selenium sulfide, zinc pyrithione) 4
- Prescription-strength antifungal or corticosteroid solutions, foams, or oils for refractory cases
- Keratolytic shampoos and lotions for thick, scaly areas 4
Facial/body seborrheic dermatitis:
- Antifungal creams (over-the-counter or prescription-strength)
- Corticosteroid creams/ointments
- Calcineurin inhibitor cream or ointment 4
Alopecia Areata
Alopecia areata is an autoimmune-mediated hair loss condition presenting as well-demarcated patches of complete hair loss, often with "exclamation mark" hairs at the periphery 5.
Differential Diagnosis Considerations
Distinguish from:
- Trichotillomania: Incomplete hair loss with firmly anchored broken hairs remaining in anagen phase 5
- Tinea capitis: Scalp inflammation present (though signs may be subtle) 5
- Early scarring alopecia
- Telogen effluvium
- Anagen effluvium (drug-induced, mimics diffuse alopecia areata) 5
Dermoscopy aids diagnosis: Regular round yellow dots indicate active disease progression; dystrophic hairs with fractured tips (exclamation mark hairs) and cadaverized hairs (fractured before scalp emergence) are characteristic 5.
Investigations are unnecessary in most cases; when diagnosis is uncertain, consider fungal culture, skin biopsy, or serology for lupus/syphilis 5. Routine iron testing is not recommended despite earlier suggestions of increased iron deficiency in women with alopecia areata 5.
Scalp Psoriasis
Scalp psoriasis presents as erythematous, scaly lesions requiring differentiation from atopic eczema, seborrheic eczema, and contact eczema 6.
Diagnosis requires:
- Inspection of entire body (psoriasis typically has extracutaneous manifestations)
- Detailed history 6
Treatment:
- Topical corticosteroids are first-line for all scalp inflammatory conditions 6
- Azole antimycotics may benefit scalp psoriasis, atopic dermatitis, and seborrheic dermatitis 6
- Immunosuppressive systemic treatments for severe cases 6
Allergic Contact Dermatitis of the Scalp
Scalp allergic contact dermatitis is commonly misdiagnosed as seborrheic dermatitis due to overlapping symptoms 7.
Atypical presentations include:
- Hair thinning and hair loss
- Erythematous lesions affecting neighboring regions 7
Diagnostic approach:
- Trichoscopy distinguishes scalp ACD: patchy distribution of thin white scales versus yellow scaling in seborrheic dermatitis 7
- Individualized patch testing with patient's personal products is essential—standardized patch testing misses 83% of cases 7
Pediculosis Capitis (Head Lice)
Pediculosis capitis is a parasitic infestation presenting with pruritus, visible nits on hair shafts, and occasionally secondary bacterial infection from scratching 8, 2, 3.
Treatment involves topical pediculicides and mechanical nit removal.
Key Diagnostic Principles
The scalp's unique features—high follicular density, high sebum production, and relatively dark, warm environment—predispose it to superficial mycotic infections and parasitic infestations 2, 3. Because common scalp conditions share similar symptoms (scaling, inflammation, hair loss, pruritus), differential diagnosis is critically important 3.
Common diagnostic pitfalls:
- Misdiagnosing kerion as bacterial abscess (though secondary bacterial infection can occur) 1
- Confusing seborrheic dermatitis with scalp allergic contact dermatitis 7
- Missing tinea capitis when inflammation is subtle 5
- Overlooking scalp ACD due to reliance on standardized rather than individualized patch testing 7