What is the diagnosis and treatment for an 18-year-old woman with a red, mildly itchy rash on her scalp and elbows, characterized by salmon-colored plaques with white scales?

Diagnosis: Plaque Psoriasis

This 18-year-old woman has plaque psoriasis (psoriasis vulgaris), and should be treated with topical corticosteroids combined with vitamin D analogues as first-line therapy for her limited disease.

Clinical Diagnosis

The clinical presentation is characteristic of plaque psoriasis:

• Salmon-colored (erythematous) plaques with white (silvery) scales on the scalp and elbows are pathognomonic for psoriasis vulgaris 1
• Classic distribution involving extensor surfaces (elbows) and scalp represents typical locations for plaque psoriasis 1, 2
• Mild pruritus is commonly associated with psoriasis, though the severity varies 1, 3
• The chronic nature (4 months duration) is consistent with psoriasis as a chronic inflammatory disease that waxes and wanes 1

Important caveat: The absence of pinpoint bleeding (Auspitz sign) when scales are removed does NOT exclude psoriasis. While this finding can support the diagnosis when present, its absence is not diagnostically significant 4.

The diagnosis of psoriasis is primarily clinical, based on pattern recognition of morphologic features and distribution 4. Skin biopsy is generally not necessary unless the diagnosis is uncertain 4.

Disease Severity Assessment

This patient has mild psoriasis based on:

• Limited body surface area (BSA) involvement: scalp and elbows only suggest <3% BSA, which defines mild disease 1
• No evidence of joint involvement (psoriatic arthritis) 1
• Mild symptoms (mild pruritus) 3

Treatment Approach

First-Line Treatment for Mild Disease

Topical therapy is the cornerstone of treatment for mild psoriasis:

• High-potency topical corticosteroids are recommended as first-line therapy 1
• Combination with vitamin D analogues (such as calcipotriene) enhances efficacy and is recommended 1, 2
• Apply to affected areas on scalp and elbows 1

Scalp-Specific Considerations

For scalp involvement specifically:

• Scalp formulations of corticosteroids and vitamin D analogues (solutions, foams, or shampoos) improve penetration through hair 1
• Consider keratolytic agents (salicylic acid) to help remove thick scale if present 2

Alternative Topical Options

If first-line therapy is insufficient or not tolerated:

• Tazarotene (topical retinoid) is an alternative for mild to moderate disease 1, 5
• Topical calcineurin inhibitors can be used, particularly for sensitive areas 2

When to Escalate Therapy

Consider systemic therapy or phototherapy if:

• BSA involvement exceeds 3-10% (moderate disease) or >10% (severe disease) 1
• Significant impact on quality of life despite limited BSA 1
• Inadequate response to topical therapy after appropriate trial 5, 2
• Development of psoriatic arthritis (joint pain, swelling, stiffness) 1

Systemic Treatment Options (if needed)

For moderate to severe disease, biologics are recommended as first-line systemic therapy 2:

• TNF-α inhibitors: etanercept, adalimumab 1, 2
• IL-17 inhibitors: secukinumab, ixekizumab 2
• IL-23 inhibitors: guselkumab, risankizumab 2
• Traditional systemic agents: methotrexate, acitretin, cyclosporine 5, 2
• Narrowband UV-B phototherapy is effective for moderate to severe disease 2

Monitoring and Follow-up

• Assess pruritus severity using visual analog scale (VAS) or numeric rating scale (NRS), as significant pruritus requires specific management 3
• Screen for psoriatic arthritis as up to 25-30% of psoriasis patients develop joint involvement 1
• Evaluate for comorbidities: cardiovascular disease, metabolic syndrome, diabetes, inflammatory bowel disease, depression 1, 5, 6

Lifestyle Modifications

Recommend:

• Maintain ideal body weight 5
• Avoid tobacco products 5
• Limit alcohol consumption 5
• Stress reduction techniques 5