Differential diagnosis of red scalp: the importance of trichoscopy

Red scalp is a common complaint that may constitute a diagnostic and therapeutic challenge in daily clinical practice. Among the numerous diseases to cause diffuse scalp erythema are psoriasis, seborrhoeic dermatitis, contact dermatitis, diffuse lichen planopilaris, dermatomyositis and scalp rosacea. Accurate diagnosis is crucial for optimal treatment outcomes. Histology most frequently discriminates the underlying condition, but it requires scalp biopsy. In many cases, the combination of clinical examination and trichoscopy is sufficient for establishing the correct diagnosis. The main trichoscopic features of psoriasis are silver-white scaling, regularly distributed dotted (glomerular) vessels or twisted red loops, and punctate haemorrhages. Yellowish-white scaling and thin arborizing vessels are typical features of seborrhoeic dermatitis. Contact dermatitis is characterized by the presence of yellow exudate and polymorphic vessels, while perifollicular scaling and erythema with the lack of follicular openings are typical findings in lichen planopilaris. In scalp dermatomyositis, tortuous and arborizing vessels with interfollicular and perifollicular pigmentation may be detected. The most characteristic features of scalp rosacea are perifollicular scaling and polygonal/arborizing vessels. This review also summarizes histological features and therapeutic options for these conditions.