Dissecting cellulitis of the scalp, also known as perifolliculitis capitis abscedens et suffodiens (PCAS), is a neutrophilic scarring alopecia with an abnormal inflammatory response to staphylococcal antigens. This association is linked to a propensity for follicular occlusion and dramatic secondary inflammatory changes to proinflammatory stimuli, such as bacterial infection. The follicle occludes, dilates, and ruptures, and the keratin promotes an inflammatory response in conjunction with a secondary staphylococcal infection attracting neutrophils.
The condition typically affects black men between the ages of 20 and 40, but it can occur in other ethnicities, in women, and in children. Dissecting cellulitis usually affects the vertex (although the entire scalp can be involved), producing boggy or fluctuant pustules and nodules. Patients complain of pain and of a disfiguring appearance. If a nodule is pressed, pus or serosanguineous fluid may extrude from one or more of the orifices.
The disease may wax and wane over several years, later producing dermal fibrosis, sinus tracts, and hypertrophic scarring with alopecia. There is an increased risk of squamous cell carcinoma in patients with long-standing disease.
In contrast to classic cellulitis, dissecting cellulitis of the scalp demonstrates prominent nodularity. Lesions may be fluctuant and/or draining. Location and patient demographic factors, such as race, are important diagnostic clues.
Codes
ICD10CM: L66.3 – Perifolliculitis capitis abscedens
SNOMEDCT: 77333008 – Dissecting cellulitis of scalp
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Differential Diagnosis & Pitfalls
Acne (folliculitis) keloidalis nuchae – Presents on the occipital scalp and nape of neck with follicular papules and pustules. A skin biopsy reveals chronic inflammation, diffuse destruction of hair follicles, scarring, and fibrosis.
Folliculitis decalvans – Presents on the occipital and vertex scalp with erythematous follicular papules and pustules with scarring and yellow-gray scale surrounding the follicle. There may be erosions, hemorrhagic crust, and tufted hair. A skin biopsy may reveal deep perifollicular or intrafollicular mixed infiltrate of lymphocytes, histiocytes, or plasma cells without abscess or sinus tract formation.
Cellulitis or erysipelas – In contrast to classic cellulitis, dissecting cellulitis of the scalp demonstrates prominent nodularity.
