Perifolliculitis capitis abscedens et suffodiens (PCAS) usually begins as a simple folliculitis, most often of the vertex and/or occiput, with clusters of perifollicular pustules rapidly followed by abscess and sinus formation.
Nodules range from a few millimeters to several centimeters in diameter and may be firm or fluctuant. Seropurulent fluid may be expressed from fluctuant nodules. Lesions may persist for years and frequently heal with a scarring alopecia. No systemic symptoms are usually evident. PCAS has a strong tendency to recur.
Tender nodules - Some of which discharge pus or blood (see the first image below)
Intercommunicating sinuses between nodules
Patchy, scarring alopecia (see the second image below)
Under dermoscopy of patches of alopecia in dissecting cellulitis - Yellow dots, red dots, empty follicular openings, black dots, and cadaverized hairs without evidence of exclamation mark hairs A white patient with painful nodules. Image used with permission from Medical Science Monitor, 2000, 6(3): 602-4.Side view of a black man with painful cutaneous nodules and patchy alopecia, characteristic of perifolliculitis capitis abscedens et suffodiens.