Laboratory Studies
Bacterial culture and sensitivity testing of acne keloidalis nuchae (AKN) lesions and draining sinuses should be considered. If pathogenic microorganisms are identified, appropriate antibiotics should be prescribed.
Procedures
A biopsy may be performed if the clinical presentation is atypical and to exclude other similar conditions.
Histologic Findings
The histological findings vary depending on the timing of the biopsy. The initial infiltrate is primarily composed of neutrophils and lymphocytes that are distributed around the lower infundibulum and isthmus of the hair follicle. Subsequently, the follicle and sebaceous glands are destroyed, with liberation of the naked hair shafts into the dermis. Acute and granulomatous inflammation surrounds the free hair shafts, and, ultimately, fibrosis ensues. Scarring alopecia ensues in long-standing lesions, marked by dermal fibrosis associated with numerous plasma cells. True keloidal collagen is typically not a feature.
Often, acute and chronic inflammation may be present in the same region, because new lesions often develop adjacent to chronic lesions. Sinus tracks can be identified in long-standing lesions. Intact hair follicles at the margins may exhibit polytrichia, with more than one hair shaft noted in a single follicle, but this is physiologic for the occiput. [14] Individual early papules may also demonstrate ingrown hairs, and these may be seen clinically in patients without progressive scarring alopecia. See the images below.
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Numerous acne keloidalis papules and plaques in a white man with straight hair.
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A large acne keloidalis plaque in a bandlike distribution at the posterior occiput in an African American man.
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A large acne keloidalis plaque on the occipital region in an African American patient. This man also had perifolliculitis of the scalp and acne conglobata (the follicular occlusion triad).
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Numerous papules that have coalesced into a large plaque, within which are tufts of hairs with several hair shafts exiting the same follicular orifice.
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A dense plasma cell infiltrate surrounding a hair follicle.
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Naked hair shafts embedded within a fibrotic dermis.
