What are the possible causes and recommended treatments for itchy papules on the scalp?

Itchy Bumps on Scalp: Diagnosis and Treatment

The most likely causes of itchy papules on the scalp are seborrheic dermatitis, tinea capitis (fungal infection), folliculitis, contact dermatitis, atopic dermatitis, psoriasis, or pediculosis capitis (head lice), and treatment depends entirely on identifying the specific condition through clinical examination and, when indicated, laboratory confirmation. 1, 2

Differential Diagnosis Approach

Primary Considerations Based on Clinical Features

Seborrheic Dermatitis:

• Look for greasy yellowish scaling with itching and secondary inflammation, particularly in the scalp and other sebaceous areas 1, 3
• More pronounced in patients with Down syndrome, HIV infection, or Parkinson's disease 1
• Caused by inflammatory response to Malassezia yeast 3

Tinea Capitis (Fungal Infection):

• Presents with scaling, lymphadenopathy, and/or alopecia as cardinal signs 1
• May show black dot pattern (broken hairs), grey patches, or inflammatory kerion (painful, boggy mass with pustules) 1, 4
• Requires laboratory confirmation via scalp scraping, hair pluck, or brush sampling for microscopy and culture 1, 4

Folliculitis:

• Inflammatory papules or pustules centered on hair follicles 5
• Can be infectious (bacterial, viral, fungal) or noninfectious 5
• May require histologic confirmation if diagnosis unclear 5

Contact Dermatitis:

• Irritant type: erythema, edema, scaling, itch from direct chemical damage (shampoos, hair products) 1
• Allergic type: maculopapular, eczematous eruption in susceptible individuals exposed to nickel, cosmetics, or hearing aid materials 1

Atopic Dermatitis (Eczema):

• Chronic pruritus typically starting in childhood with involvement of multiple body areas 1
• Skin shows erythema, xerotic scaling, lichenification depending on stage 1

Pediculosis Capitis (Head Lice):

• Transmitted by head-to-head contact 6
• Papular urticaria with visible nits or lice on examination 6

Psoriasis:

• Less pruritic than eczema, lacks oozing/crusting 1
• Well-demarcated plaques with silvery scale 7, 8

Diagnostic Algorithm

Step 1: Clinical Examination

• Examine for scaling pattern, presence of alopecia, lymphadenopathy, and pustules 1, 4
• Check for greasy yellow scale (seborrheic dermatitis), broken hairs/black dots (tinea), or follicular pustules (folliculitis) 1, 3
• Inspect for nits or lice (pediculosis) 6

Step 2: When to Obtain Laboratory Confirmation

• Obtain specimens immediately if you suspect tinea capitis (presence of scaling + lymphadenopathy + alopecia, or kerion) via scalp scraping, hair pluck, or brush sampling 1, 4
• Wood's lamp examination can identify M. canis (green fluorescence) but most dermatophytes don't fluoresce 2, 4
• Dermoscopy increases diagnostic sensitivity for tinea (comma hairs, corkscrew hairs) 4

Step 3: Consider Patch Testing

• If contact dermatitis suspected, particularly with history of new hair products, hearing aids, or nickel jewelry 1
• Neomycin causes reactions in 5-15% of patients with chronic external otitis 1

Treatment by Diagnosis

Seborrheic Dermatitis

First-line: Antifungal shampoos (ketoconazole) for long-term use 3

• Topical corticosteroids only for short-term use due to adverse effects 3
• Over-the-counter antifungal shampoos should be tried first 3

Tinea Capitis

Oral systemic therapy is mandatory (topical therapy alone fails) 1, 4

• For Trichophyton species: Terbinafine 62.5 mg/day (<20 kg), 125 mg/day (20-40 kg), or 250 mg/day (>40 kg) for 2-4 weeks 1
• For Microsporum species: Griseofulvin 15-20 mg/kg/day for 6-8 weeks 1
• Add antifungal shampoo (ketoconazole 2%, selenium sulfide 1%, or povidone-iodine) to reduce spore transmission 1, 4
• Start treatment immediately if kerion present or clinical diagnosis highly suspected, don't wait for culture results 1, 4

Atopic Dermatitis

• Gentle skin care with emollients 1
• Medium-to-high potency topical corticosteroids once or twice daily for 1-4 weeks for clearance, then taper 1
• Proactive maintenance therapy with medium-strength topical corticosteroids or tacrolimus 2-3 times weekly 1
• Address trigger avoidance (irritants, detergents, sweat) 1

Contact Dermatitis

• Identify and eliminate offending agent 1
• Topical corticosteroids for inflammation 1
• Avoid neomycin-containing preparations if allergic contact dermatitis suspected 1

Folliculitis

• Bacterial: Topical or oral antibiotics depending on severity 5
• Fungal: Antifungal therapy 5
• Noninfectious: May require biopsy and specialized treatment 5

Pediculosis Capitis

First-line: Malathion lotion 0.5% left on for 30 minutes to 8 hours, repeated in one week 6

• Alternative: Spinosad topical suspension 0.9% for 10 minutes, repeated in one week 6
• Treat close contacts to prevent reinfection 6

Critical Pitfalls to Avoid

• Never treat tinea capitis with topical therapy alone—it will fail and prolong transmission 1
• Don't confuse kerion with bacterial abscess—it's a fungal inflammatory response requiring oral antifungals, not just antibiotics 1, 2, 4
• Don't stop tinea treatment based on clinical improvement alone—continue until mycological clearance documented 4
• Avoid prolonged topical corticosteroid use for seborrheic dermatitis due to adverse effects 3
• Don't overlook secondary bacterial infection in kerion despite its fungal etiology 2, 4