Psoriasis Vulgaris Auspitz Sign

A 38-year-old man presents with a five-year history of symmetrical scaly patches on his elbows, knees, and scalp that worsen during winter and after a recent streptococcal sore throat. He recently started a beta-blocker for hypertension and noticed the plaques thickened. On examination, the structure marked **B** shows well-demarcated erythematous plaques with thick silvery-white micaceous scale on extensor surfaces. When the scale is gently scraped with a glass slide, pinpoint bleeding points appear across the plaque surface. Which of the following best explains the clinical sign elicited by gentle scraping in this condition?