The correct answer is perioral dermatitis (POD; choice “c”), an extremely common dermatosis that often begins in the perinasal area, spreading downward with time.
Impetigo (choice “a”) does not bear much resemblance to POD and would have responded quite well to the course of cephalexin.
Lupus (choice “b”) belongs in the differential, given the patient’s gender and the condition’s chronicity; however, this condition typically prefers the lateral face, usually causes focal atrophy, and does not manifest with pustules and papules.
Had the patient not responded to medication for POD, a punch biopsy would have been a reasonable step to rule out lupus and psoriasis (choice “d”), which can present in a similar manner, though seldom as the sole manifestation of that disease.
POD is an eruption of unknown etiology that demonstrates the clinical features of several other conditions (including eczema, seborrhea, and acne). It is therefore often difficult to diagnose—especially when it has been present for so long and has been treated with several medications.
More than 90% of POD cases occur in women ages 24 to 50, which suggests a possible role for hormones, makeup, or facial products. Yet none of these factors has been specifically implicated in the condition’s genesis.
Indeed, virtually every woman with POD presents with a history of having changed her makeup and other facial products, often many times, to no good effect. Stress has also been suggested as a contributing factor, and indeed appears, to many dermatology providers, to be the culprit; however, this has yet to be proven.
What is known is that in a large percentage of cases, the chronic application of topical steroids either brings on POD or worsens it, thereby necessitating questions about steroid use. Many a patient with seborrhea has successfully treated that disease with topical steroids only to create POD—which she naturally treats with more and more steroid.
The histologic picture of POD is similar to rosacea. But unlike POD, the latter spares the concave areas of the face. Like rosacea, POD responds so readily to oral tetracycline (alternatives including minocycline, amoxicillin, and erythromycin) that treatment success essentially verifies the diagnosis. Simply knowing that POD is utterly common is extremely helpful in the development of any differential of facial eruptions.
This particular patient responded quite well to a course of tetracycline (500 mg bid for a month, then 500 qd for another month), at the end of which her skin was totally clear. While her lack of response to topical antibiotics is typical of POD, many women with this condition actually report significant irritation with these products.