Acne Keloidalis nuchae is a disease primarily of African-American males aged 14–25 years, but Hispanic teenage males can be affected and lesions can be seen rarely in Caucasian or female adolescents.

Lesions beginning before puberty or in persons older than 50 is uncommon [3]. Glenn et al. reported a prevalence of 0.45 % in the African-American population [4]. Knable et al. found a prevalence of 8.2 % (13.6 % blacks, 0 % in whites) in an all male American football player population in Indiana aged 14–27 years old, with players beyond the high school level 10.3 times more likely to have AKN than at the high school level. Additionally, they found that black players were 8.5 times more likely to have AKN lesions than white players. Football players appear to be at higher risk due to friction and irritation from their helmets [5].

The incidence of AKN has been reported to be 9.4 % in Nigeria [2], 3.5 % in Cape town (10.5 % in men and 0.3 % women) [6], and 0.7 % in Benin [3]. In an Afro-Caribbean population in Jamaica, AKN was the eighth most common dermatosis, accounting for 1.74 % of all skin diseases in a dermatological clinic [7]. In a dermatology clinic in London, AKN was the most frequently seen disease among adult black patients, consisting of 13.7 % of their referrals [8]. South African school children had a prevalence of 0.67 %, exclusively in boys [9]. Additionally, while males are particularly affected, cases have been reported in females, with a sex ratio estimated at 20:1 [10].

AKN is a disease of the hair follicles of the ventral head and neck. Diagnosis is based on typical clinical appearance and location. AKN is characterized by follicular-based papules and pustules over the occipital/nuchal areas of the scalp, as well as on the nape of the neck. Early AKN lesions will present as dome-shaped papules 2–4 mm in the nape or occipital scalp. They are usually asymptomatic, but pustules may also occur which often may be pruritic or painful. Broken hair shafts or ingrown hairs can be seen within or at the margin of the plaques. They will not be present for long periods due to patient’s tendency to scratch early lesions off.

Lesions of AKN often heal with keloids, hence the origin of the name. Small keloidal lesions can cause scarring alopecia and may coalesce into larger plaques that are a few centimeters large [11]. Tenderness to the touch may be associated with inflammatory lesions of AKN. Scarring alopecia can result in complete loss of hair or scarred follicles with altered growth tracts and multiple hairs erupting from the keloidal lesions.

Keloids formed in the setting of AKN are likely to spread beyond the site of initial appearance and may ultimately coalesce and develop into tumor-like masses. Advanced cases may progress to form abscesses and sinus tracts. Purulent discharge may occur. Subcutaneous abscesses with draining sinuses may be malodorous.

Salami et al. found that 60 % of patients thought about their lesions all the time, while 40 % have poor sexual relations [2]. Additionally, the pustular lesions may be pruritic and painful.

The differential diagnosis includes acne conglobata, acne vulgaris, acneiform eruptions, bacterial folliculitis, folliculitis decalvans, hidradenitis suppurativa, dissecting cellulitis and perifolliculitis capitis abscedens et suffodiens. Although these illnesses bear some similarity to AKN, the clinical features of AKN are extremely characteristic in most cases; in particular the location and the morphology of lesions are often distinctive.

The exact etiology of AKN is unknown, although several hypotheses have been suggested and the pathogenesis appears to be multifactorial. Shapero et al. postulate that folliculitis is mechanically induced by rubbing, scratching, or irritation and chronic folliculitis results in healing with scar and keloid formation [12]. This is supported in an analysis of 453 football players in Indiana; 13.6 % were positive for AKN, suggesting friction from helmet padding [5].

Hair cuts seem to be an inciting factor in many cases. 90 % of AKN consultations at a clinic in Nigeria had preceding haircuts [2]. In a study of 1,916 patients in Cape Town, South Africa, the highest prevalence was among those who receive haircuts using razors or clippers, and especially among those who experienced bleeding trauma from closely shaven haircuts [13]. Finally, in another South African study of 1,042 school children, prevalence was higher in those who received frequent haircuts, confirming this as a risk factor [9].

Kelly suggests that AKN may share similarities with pseudofolliculitis barbae, a follicular disorder of the beard area, common among African-American men who shave with razors. When tightly curled hair, common to Blacks/African Americans, is shaven, newly curled hair may have growth under the skin (ingrown hairs), causing a chronic progressive foreign body inflammatory reaction [10]. However, in a blinded study of histological AKN slides, no evidence was found of ingrowing hairs curving into the skin. Instead, Sperling et al. suggest that AKN is a primary scarring alopecia [11]. Additionally, no histological evidence was found by Sperling et al. of a transepithelial canal as suggested by Goette and Berger [14].

George et al. suggest AKN is frequently associated with male gender, seborrheic constitution, early reproductive years, and increased fasting blood testosterone [15]. AKN is also associated with lichen simplex chronicus with fibrotic keloidal scarring [16]. It has also been associated with acne mechanica by Knable et al. [5]. However, the hallmark of acne mechanica are comedones, which are absent in AKN [15]. AKN and acne keloidalis-like lesions is also associated with low-grade bacterial infection, superinfection [15], autoimmune processes, anticonvulsant medications [17], and physical or emotional stress [18].

AKN has also been described in two patients with keratosis follicularis spinulosa decalvans [19, 20], and as a cutaneous marker for metabolic syndrome [21]. Cases have also occurred in Caucasian patients after cyclosporine use, suggesting that the follicle is the primary site of initial lesions [22, 23].

Histologically, there is follicular and perifollicular inflammatory infiltrate, which changes composition with the progression of AKN. Initially, the infiltrate is composed primarily of neutrophils and lymphocytes in the lower infundibulum and isthmus of the hair follicle, and some reports mention the predominance of mast cells early on. As the lesion advances, the hair follicle and sebaceous glands rupture and granulomatous infiltrate develops around the free hair fragment. Dermal fibrosis and scars are seen here as the hair continues to proliferate beneath fibrous tissue [24]. Scarring alopecia may occur, which may be seen by dermal fibrosis associated with numerous plasma cells. Also as AKN is not a true keloid, keloidal collagen will not typically be found.

There is currently no evidence of a genetic component to AKN. However, there are twice the number of mast cells in the posterior scalp relative to individuals with AKN [15]. This higher density may contribute to pruritus and thus mechanical manipulation of the region, thus suggesting a genetic predisposition. Furthermore mast cells are often present in keloids and may aggravate disease.