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This condition was first described in 1888 by Quinquaud as being an “epilating and destructive folliculitis of the hairy regions”. As it progresses it eventually results in cicatricial (scarring) alopecia. Quinquaud had already isolated a bacterium from within the affected follicles. In 1905 Brocq gave Quinquaud’s folliculitis the name of folliculitis decalvans, drawing a distinction between it and other types of cicatricial alopecia.
The exact incidence of folliculitis decalvans is unknown but it is a rare condition. According to case series, it accounts for 11% of cases of primary cicatricial alopecia  . It mainly affects young people and middle-aged adults, with a slight predilection in males. Folliculitis decalvans seems to be more common in people of African descent.
The precise aetiology of this condition is unknown. In some cases it is caused by an S. aureus infection and in others, by an inflammatory pathology. Staphylococcus aureus is isolated from bacterial specimens in the majority of patients although these may only be findings of non-pathogenic bacteria. An abnormal host immune response to the staphylococci bacteria has been postulated, which could explain the chronic and cicatricial pattern of progression in this type of folliculitis. There is one report of extensive folliculitis decalvans in an HIV-positive patient during the weeks following initiation of triple-combination antiretroviral therapy . In a series of 18 patients , no immune abnormality could be proven, while bacteriology samples did show staphylococcus aureus in all cases. A theory of genetic predisposition has been proposed, as there have been familial cases . A recent publication was able to demonstrate the presence of a bacterial biofilm on the infundibulum of affected hair follicles for the first time in Quinquaud’s folliculitis, and this could explain the recurrent character of this condition .
Folliculitis decalvans is usually sited on the cranial vertex and the occipital region, and although other hairy areas of the body can be affected, these are exceptional cases. The condition can begin after a trauma to the scalp. Clinically it begins with a follicular lesion that firstly causes perifollicular erythema, and then a pustule the size of a pinhead with the hair at its centre develops. A crust forms next, which later detaches taking the hair with it. Outbreaks of pustules occur repeatedly, destroying the hair follicle. Little by little patches of scarring alopecia build up that vary in size, and they may be rounded or oval, and pinkish or ivory-white in colour. At the peripheries of these, the active folliculitis lesions are situated. Erythema, yellowish or haemorrhagic crusts, hyperkeratosis, or erosions may be present around the follicles. The areas of alopecia are often thicker and more indurated than in other types of scarring alopecia. These patches of alopecia coalesce resulting in a pattern of slow-spreading alopecia with spherical and flat edges. The most longstanding affected areas have a scarring appearance with no active folliculitis lesion. Disease progression is chronic and it can lead to alopecia with a very striking appearance. Patients often complain of pain, pruritus, or a burning sensation. The lesions may bleed spontaneously with the patient finding bloodstains on their pillow on waking in the morning. Tufted hair follicular lesions are common in Quinquaud’s folliculitis; this is when several (5 - 20) hairs emerge from a single dilated follicular opening. Some authors have put forward the theory that tufted hair folliculitis could be a specific form of folliculitis decalvans . In fact, tufted hair folliculitis lesions can be seen in Quinquaud’s folliculitis decalvans but also in other types of cicatricial alopecia such as acne keloidalis nuchae or dissecting cellulitis of the scalp, from the point when the infundibula of adjacent follicles are destroyed and scarring occurs, resulting in the formation of a single enlarged infundibulum.
Diagnosis can be aided by carrying out a dermatoscopic examination of the scalp to confirm that the alopecia is scarring, due to the finding of a loss of follicular ostia. Further dermatoscopic findings are erythema, pustules, and crusts around the affected follicles, as well as tufted hairs.
It is crucial to take samples for bacterial and fungal cultures. The sample for bacteriology is taken from an intact pustule, and this will allow S. aureus to be isolated and an assessment can be made of the bacterium’s sensitivity to various antibiotics.
Histologically, Quinquaud’s folliculitis decalvans belongs to the group of primary cicatricial alopecias caused by neutrophilic inflammation. A 4 mm punch biopsy is carried out in the active area and the specimen should include hairs following the direction in which they emerge with horizontal cross-sections taken. In the initial lesions, there is a polymorphonuclear neutrophilic infiltrate around the follicle and in the adjacent dermis. The sebaceous glands are destroyed early on. The neutrophils are later succeeded by lymphocytes, plasma cells, and sometimes giant cells that can produce a granulomatous response. The hair follicle is then destroyed and in its place is an area of scarring fibrosis. At a later stage, only the fibrous scar tissue that replaces the destroyed hair follicles can be seen.
Other pustular conditions of the scalp must be excluded, firstly kerion, by taking a sample for fungal cultures, which is crucial in all cases of folliculitis of the scalp. There are several published cases of ringworm of the scalp mimicking Quinquaud’s folliculitis decalvans. Erosive pustulosis of the scalp occurs in females over the age of 70 and it is caused by a trauma. It combines pustular and crusted lesions on the cranial vertex and occipital region, which progress to become a scarring alopecia. Under the crusts, the scalp appears to be erosive. Dissecting cellulitis of the scalp mainly affects black men. It begins with a simple suppurative folliculitis but the areas of folliculitis progress until deep, fluctuant and coalescing nodules are formed on the scalp, which is not seen in Quinquaud’s folliculitis decalvans. Cases of Quinquaud’s folliculitis decalvans developing into acne keloidalis nuchae are sometimes seen. Lichen planopilaris belongs to the group of primary cicatricial alopecias caused by lymphocytic inflammation. However, in some cases of lichen planopilaris, pustules may be seen due to a secondary infection .
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