The differential includes various scarring, nonscarring alopecias
Since clinical findings of FD can range from relatively nonspecific mild disease at its onset to the end stage described above, a detailed patient history is needed. The following scarring and nonscarring alopecias should be considered in the diff erential diagnosis: dissecting cellulitis of the scalp, central centrifugal cicatricial alopecia (CCCA), acne keloidalis nuchae, erosive pustular dermatosis, lichen planopilaris (LPP), inflammatory tinea capitis, and secondary syphilis.
Dissecting cellulitis of the scalp is a distinctive, often debilitating disease commonly seen in young adult African American men. It is considered part of the follicular occlusion tetrad that also includes hidradenitis suppurativa, acne conglobata, and pilonidal cysts. It presents as a scarring alopecia with firm scalp nodules that rapidly develop into boggy, fluctuant, oval to linear sinuses that may eventually discharge purulent material.
In contrast to FD, dissecting scalp cellulitis lesions interconnect via sinus tract formation so that pressure on one fluctuant area may result in purulent discharge from perfo-rations several centimeters away.5 Although both dissecting cellulitis and FD are considered primary neutrophilic scarring alopecias, the presence of true sinus tract formation can be a distinguishing finding.
CCCA is the most common form of scarring alopecia among African Americans and is particularly seen among African American women.5 It generally presents on the scalp vertex like FD, but it is much less inflamma-tory and typically causes only mild pruritus or tenderness of the involved areas.
Although numerous theories have been suggested, the etiology is unknown. The pathogenesis is thought to be associated with premature desquamation of the inner root sheath, which can be demonstrated on biopsy. Also seen histologically is lymphocytic perifollicular inflammation and polytrichia.6