Folliculitis; furuncle; carbuncle; hidradenitis suppurativa — expanded notes
Folliculitis
Folliculitis is inflammation centred on the hair follicle. Infectious causes include Staphylococcus aureus, Pseudomonas and Malassezia; non-infectious causes include friction, occlusion, shaving and drug-related eruptions. Monomorphic itchy follicular papules/pustules on the upper trunk suggest Malassezia folliculitis; hot-tub exposure suggests Pseudomonas. Culture is useful in recurrent, severe or treatment-resistant disease.
Furuncle and carbuncle
A furuncle is a deep follicular infection with perifollicular abscess formation, usually due to S. aureus. A carbuncle is a cluster of interconnected furuncles with deeper suppuration and multiple drainage points. Assess for fluctuance, cellulitis, fever, diabetes and immunosuppression. Incision and drainage is central for a fluctuant abscess; antibiotics are added for systemic illness, surrounding cellulitis, multiple lesions or high-risk patients.
Hidradenitis suppurativa: pathogenesis
HS is a chronic inflammatory follicular disease, not simply recurrent infection. Follicular occlusion and rupture initiate inflammation, leading to painful nodules, abscesses, tunnels and scarring. It affects intertriginous sites and is associated with smoking, obesity, family history, metabolic syndrome and inflammatory bowel disease.
Diagnosis and staging
Diagnosis is clinical, based on typical lesions, typical locations and recurrence. Look for double-ended comedones, draining tunnels and rope-like scars. Hurley I has abscesses without tunnels/scarring; Hurley II has recurrent abscesses with separated tunnels/scars; Hurley III has diffuse interconnected disease.
Management
General measures include smoking cessation, weight management where relevant, friction reduction, wound care and pain management. Mild disease may be treated with topical clindamycin or antiseptic washes; oral tetracyclines are often used for inflammatory disease. More severe disease may require combination antibiotics, biologics targeting TNF or IL-17 pathways, and surgery such as deroofing or excision. Simple incision and drainage may relieve acute pain but recurrence is common. Screen for comorbidities and assess psychological impact.