Scarring alopecia and the dermatopathologist.

BACKGROUND: The evaluation of patients with cicatricial alopecia is particularly challenging, and dermatopathologists receive little training in the interpretation of scalp biopsy specimens. Accurate interpretation of specimens from patients with hair disease requires both qualitative (morphology of follicles, inflammation, fibrosis, etc.) and quantitative (size, number, follicular phase) information. Much of this data can only be obtained from transverse sections. In most cases, good clinical/pathologic correlation is required, and so clinicians should be expected to provide demographic information as well as a brief description of the pattern of hair loss and a clinical differential diagnosis.
RESULTS: The criteria used to classify the various forms of cicatricial alopecia are relatively imprecise, and so classification is controversial and in a state of evolution. There are five fairly distinctive forms of cicatricial alopecia: 1) chronic, cutaneous lupus erythematosus (discoid LE); 2) lichen planopilaris; 3) dissecting cellulitis (perifolliculitis abscedens et suffodiens); 4) acne keloidalis; and 5) central, centrifugal scarring alopecia (follicular degeneration syndrome, folliculitis decalvans, pseudopelade). Not all patients with cicatricial alopecia can be confidently assigned to one of these five entities, and "cicatricial alopecia, unclassified" would be an appropriate label for such cases.
CONCLUSION: The histologic features of five forms of cicatricial alopecia are reviewed. Dermatopathologists can utilize a "checklist" to catalog the diagnostic features of scalp biopsy specimens. In many, but not all, cases the information thus acquired will "match" the clinical and histologic characteristics of a form of cicatricial alopecia. However, because of histologic and clinical overlap between the forms of cicatricial alopecia, a definitive diagnosis cannot always be rendered.