The correct answer is petaloid seborrheic dermatitis (choice “d”), named for the flowerlike appearance of its polycyclic borders. Psoriasis (choice “a”) can present in this area, but tends to be scalier and usually involves multiple areas (eg, elbows, knees, and nails).
Rashes like this patient’s are often termed yeast infection (choice “b”). However, while a commensal yeast (Pityrosporum) can play a role in its formation, it appears that seborrhea represents an idiosyncratic reaction to increased numbers of this organism, rather than an actual infection.
Bowen’s disease (choice “c”) is a superficial squamous cell carcinoma, usually caused by overexposure to sunlight. Its lesions will be fixed, slowly growing larger with time, while seborrheic dermatitis will typically come and go. Biopsy is sometimes necessary to distinguish one from the other.
Seborrheic dermatitis (SD, aka seborrhea) is common, affecting up to 5% of the population. Dandruff is its usual manifestation, but it affects numerous other areas (as in this case), including the axillae, groin, beard, and genitals.
Presenting with scaling on an erythematous base, SD often flares and remits with the season (especially winter), with stress, and with increases in alcohol intake. Although it is usually mild, some cases can be severe. SD is associated with or accentuated by several other conditions, including Parkinson’s, stroke, and HIV. Severe SD in infants raises the possibility of Langerhans cell histiocytosis, especially when the presentation is atypical.
The diagnosis of SD can be difficult when it appears elsewhere than the scalp and face (eg, as an axillary or genital rash). Likewise, sternal petaloid SD is mystifying, unless other corroboratory manifestations are sought and found.
A few patients show signs of SD and psoriasis such that a definitive diagnosis cannot be made. Such overlap cases are sometimes termed sebopsoriasis. But psoriasis will usually exhibit signs not seen with SD, such as pitting of the nails, involvement of extensor surfaces of elbows and knees, and characteristic signs of psoriatic arthropathy in about 20% of cases. Pinpoint bleeding caused by peeling away scale, called the Auspitz sign, is seen with psoriasis and not with SD.
This patient’s chest involvement responded rapidly to topical betamethasone foam, quickly tapered to avoid thinning the skin. Less powerful steroid creams, lotions, or gels (eg, triamcinolone 0.025%) can be used on other areas, such as ears and face. The daily use of an OTC dandruff shampoo (containing selenium sulfide, zinc pyrithione, tar, or ketoconazole) is an effective approach to controlling scalp involvement, but the product should be changed weekly.
Once the initial inflammation is controlled, topical antiyeast/antifungal preparations (eg, ketoconazole cream or any of the imidazoles, such as clotrimazole or oxiconazole) can be useful.
Finally, emphasis must be placed on educating the patient to expect control of the condition but not a cure.