Multiple firm papules and nodules: Located on the posterior scalp and nuchal region, extending into the hairline. Follicular involvement: Many lesions appear to be centered around hair follicles. Coalescence: Some papules and nodules have coalesced to form larger, irregular plaques. Scarring and hypopigmentation: Evidence of chronic inflammation with areas of scarring and altered pigmentation. Alopecia:* Hair loss is visible within the affected scarred areas.
AKN, also known as folliculitis keloidalis nuchae, is characterized by chronic inflammation of the hair follicles, leading to papules, pustules, and eventually keloidal scarring and permanent hair loss (cicatricial alopecia). It is more common in young men with curly hair, particularly those of African descent. The exact etiology is unknown but is thought to involve chronic irritation, ingrown hairs, and a foreign body reaction to hair shaft fragments.
| Feature | Acne Keloidalis Nuchae (AKN) | Folliculitis Decalvans | Dissecting Cellulitis of the Scalp | Tinea Capitis (Inflammatory) |
|---|---|---|---|---|
| Location | Posterior scalp, nuchal region | Vertex, crown, occiput | Vertex, occiput, diffuse | Any scalp area |
| Primary Lesions | Firm papules, nodules, keloidal scars | Pustules, erosions, crusts, tufted hairs | Boggy nodules, interconnected sinuses, purulent discharge | Erythematous, scaly patches, pustules, kerion |
| Scarring | Prominent keloidal scarring, cicatricial alopecia | Cicatricial alopecia | Extensive scarring, sinus tracts | Variable, can cause scarring alopecia (kerion) |
| Associated Lymph | Reactive cervical lymphadenopathy (if severe/infected) | May have reactive lymphadenopathy | May have reactive lymphadenopathy | Reactive lymphadenopathy (especially with kerion) |
| Hair | Permanent hair loss in affected areas | Tufted hairs (multiple hairs emerging from one follicle) | Permanent hair loss, often with purulent discharge | Broken hairs, black dots, scaling, sometimes kerion |
Bolognia, Jean L., et al. Dermatology. 4th ed., Elsevier, 2018, Ch 71, p. 1205-1206
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