How can I differentiate seborrheic capitis, sebopsoriasis, and scalp psoriasis and what are the appropriate management strategies for each?

Differentiating Seborrheic Capitis, Sebopsoriasis, and Scalp Psoriasis

Seborrheic dermatitis (seborrheic capitis) presents with blurred dark-red erythema and yellowish greasy scales without crossing the hairline, while scalp psoriasis shows sharply demarcated erythematosquamous plaques that extend beyond the hairline, and sebopsoriasis represents an overlap condition with features of both diseases that can be diagnostically challenging. 1

Clinical Differentiation

Scalp Psoriasis Features

• Sharply demarcated, thick silvery-white scales that extend across the natural hairline onto the forehead, neck, and behind ears 1
• Well-defined erythematous plaques with distinct borders 2
• Hair loss is uncommon unless related to therapeutic agents 1
• More intense inflammation compared to seborrheic dermatitis 3

Seborrheic Dermatitis (Seborrheic Capitis) Features

• Blurred, poorly demarcated dark-red erythema with yellowish, greasy scales that respect the hairline 1
• Diffuse alopecia frequently present due to telogen effluvium from chronic inflammation 4, 1
• Scaling is less thick and more oily in character 1
• Associated with Malassezia species colonization 4

Sebopsoriasis (Overlap Condition)

• Exhibits features of both conditions simultaneously, making definitive diagnosis difficult 3, 5
• May represent seborrheic dermatitis transforming into psoriasis in genetically predisposed individuals via Köbner phenomenon 5
• Clinical and histopathological features overlap significantly 3

Dermoscopic Differentiation

Dermoscopy provides valuable diagnostic clues when clinical examination is equivocal. 2

Psoriasis Dermoscopic Findings

• Red dots and globules (RDG) - most characteristic feature 2, 6
• Twisted red loops and glomerular vessels 2
• Signet ring vessels (SRV) - newly described specific finding 6
• Hidden hairs (HH) - newly described specific finding 6
• Structureless red areas 6

Seborrheic Dermatitis Dermoscopic Findings

• Arborizing vessels - characteristic pattern 2, 6
• Atypical red vessels with absence of red dots and globules 2
• Comma vessels (CV) - specific for seborrheic dermatitis 6
• Featureless areas devoid of particular vascular patterns 2
• Twisted red loops (less common than in psoriasis) 6

Histopathological Differentiation

When clinical and dermoscopic findings remain inconclusive, histopathology can provide definitive diagnosis. 3

Psoriasis Histopathology

• Mounds of parakeratosis with neutrophils - strong diagnostic criterion 3
• Spongiform micropustules of Kogoj 3
• Clubbed and evenly elongated rete ridges 3
• Increased mitotic figures (≥6 per high-powered field) 3
• PAS-reactive serum inclusions and Munro abscesses 5

Seborrheic Dermatitis Histopathology

• Follicular plugging - strong diagnostic criterion 3
• Shoulder parakeratosis 3
• Prominent lymphocytic exocytosis 3
• Irregular acanthosis with relatively thin horny layer 5
• Spongiosis and spongiotic vesicles 5

Note: Immunohistochemistry (Ki-67, keratin 10, caspase-5, GLUT-1) does not help differentiate these conditions. 3

Management Strategies

Scalp Psoriasis Management

• Topical corticosteroids combined with vitamin D derivatives as first-line therapy 1
• Topical therapy alone may be insufficient for extensive disease 1
• Systemic therapy indicated for severe or widespread disease: methotrexate, fumarates, cyclosporine, or biologics 1
• Long-term, consistent treatment required with patient counseling on adherence 1

Seborrheic Dermatitis Management

• Topical corticosteroids (low-potency, short-term) to control inflammation and itching 4, 1
• Antifungal agents (ketoconazole shampoo) targeting Malassezia species 1
• Avoid long-term corticosteroid use due to risk of skin atrophy, telangiectasia, and tachyphylaxis 4
• Gentle cleansers and emollients to reduce dryness 4
• Avoid alcohol-containing preparations 4
• Maintenance therapy with intermittent anti-inflammatory treatment necessary due to chronic relapsing nature 4
• Systemic therapy rarely needed; when required, use corticosteroids, antifungals, or vitamin A derivatives 1

Sebopsoriasis Management

• Treat based on predominant clinical features 3
• May require combination approach using both antifungal and vitamin D derivative therapies 1
• Monitor response and adjust treatment based on clinical evolution 5

Critical Pitfalls to Avoid

• Do not confuse seborrheic dermatitis with permanent scarring alopecias - hair regrowth is excellent once inflammation is controlled 4
• Do not use long-term facial corticosteroids in seborrheic dermatitis due to atrophy risk 4
• Do not assume hair loss in psoriasis is disease-related - it may be treatment-induced 1
• Do not rely solely on scale characteristics - dermoscopic vascular patterns are more reliable for differentiation 2
• Consider tinea capitis in the differential diagnosis, particularly with pronounced inflammation requiring fungal culture confirmation 4