Differentials
Acne keloidalis nuchae
Acneiform eruptions
SIGNS / SYMPTOMS
Possibly caused (or exacerbated) by oral drugs (e.g., topical or systemic corticosteroids, Janus kinase inhibitors), contrast dye, testosterone, and cosmetic products.
Clinical clues include the abrupt onset of lesions within days of exposure, widespread involvement, atypical locations, atypical age, and improvement with cessation of the drug or exposure.
INVESTIGATIONS
Clinical differentiation usually suffices.
Chloracne
SIGNS / SYMPTOMS
Comedones, pustules, and cysts are most commonly found behind the ears and in the axillae and groin.
Consider exposure to halogenated aromatic hydrocarbons (e.g., chlorinated dioxins and dibenzofurans). Patient may have systemic complications such as ophthalmic, neuropathic, hepatic, or lipoprotein abnormalities.[39]
INVESTIGATIONS
Clinical differentiation usually suffices.
Consider laboratory tests such as liver enzymes and lipid panel.
Favre-Racouchot syndrome
SIGNS / SYMPTOMS
Multiple open and closed comedones on the periorbital and malar areas, usually on older people with significant chronic sun exposure. Typically non-inflammatory.
INVESTIGATIONS
Clinical differentiation usually suffices.
Skin biopsy shows increased elastic tissue with thickened, tortuous fibres in the upper and mid-dermis.[40]
Folliculitis (non-gram-negative)
SIGNS / SYMPTOMS
Common condition that manifests as erythematous papules and pustules, which are follicularly based.
As opposed to acne, folliculitis often affects the trunk and extremities.
INVESTIGATIONS
Clinical differentiation usually suffices.
Pustular lesions that do not respond to typical acne antibiotics may be cultured.
Gram-negative folliculitis
SIGNS / SYMPTOMS
Occurs in patients with acne treated with long-term antibiotics who subsequently develop pustules or nodules on the anterior nares, which then spreads. Can also occur in people after hot tub immersion, as well as in patients with HIV.
INVESTIGATIONS
Lesions may be cultured to isolate the gram-negative bacteria if acneiform lesions do not respond to typical antibiotic regimen.
Lupus miliaris disseminatus faciei
SIGNS / SYMPTOMS
Firm yellowish-brown or red smooth papules peri-orbitally and characteristically on the eyelid skin.[41]
INVESTIGATIONS
Diascopy reveals yellowish-brown lesions. Skin biopsy reveals caseating epithelioid cell granulomas.
Milia
SIGNS / SYMPTOMS
White keratinaceous cysts that are found on the face, particularly on the eyelids. Lesions are fixed and persistent.
INVESTIGATIONS
Skin biopsy shows small cysts derived from the infundibulum of the vellus hair.
Peri-oral dermatitis
SIGNS / SYMPTOMS
Common peri-oral eruption of papules and pustules on an erythematous and/or scaling base, often the result of topical corticosteroid use. Localised symmetrically around the mouth, with a clear zone around the vermilion border.[42]
INVESTIGATIONS
Clinical differentiation usually suffices.
Pyoderma faciale
SIGNS / SYMPTOMS
Rapid onset of reddish or cyanotic erythema with abscesses, cysts, and occasionally sinus tracts. No comedones and no involvement of back or chest.[43]
INVESTIGATIONS
Skin biopsy shows a grenz zone and mixed inflammatory infiltrate in the upper and mid-dermis, with extravasation of red blood cells and haemosiderin deposition.
Rosacea
SIGNS / SYMPTOMS
More typically affects older people than does acne vulgaris, most often women aged 30-50 years.
Various forms, but classically presents with background erythema and telangiectasias, and inflammatory papules and pustules occasionally superimposed.
Environmental factors often act as triggers.
INVESTIGATIONS
Clinical differentiation usually suffices. There is a lack of comedones in rosacea.
Syringoma
SIGNS / SYMPTOMS
Non-inflammatory small papules that occur primarily on the eyelids and upper cheeks, usually multiple.
Disproportionately more prevalent in Japanese women.
INVESTIGATIONS
Skin biopsy shows a dense fibrous stroma with dilated cystic spaces that have small comma-like tails resembling tadpoles.
Adenoma sebaceum (angiofibromas)
SIGNS / SYMPTOMS
Small, translucent, waxy papules distributed symmetrically over the central cheek, nose, and forehead.
Multiple lesions associated with tuberous sclerosis.[44]
INVESTIGATIONS
Skin biopsy shows dermal fibrosis and vascular proliferation and dilation.
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