HISTORY
A 48-year-old woman presents to dermatology for evaluation of “ringworm” that has been unresponsive to antifungal creams and a subsequent course of terbinafine (250 mg/d for 10 days).
The problem started several weeks ago, when she experienced mild itching in the upper intergluteal area. Her husband examined the area and noted several patches of a round, scaly rash that they assumed must be ringworm. The patient tried applying OTC clotrimazole cream twice a day, with no good effect.
She next visited a local urgent care center, where the provider agreed with the self-diagnosis. Nystatin cream was prescribed for twice-daily use, but this treatment was also unsuccessful.
Next up was the patient’s primary care provider, who reiterated the diagnosis of ringworm and prescribed the aforementioned course of terbinafine. When it too failed, the patient, still worried, requested a referral to dermatology.
During the history taking, it is revealed that the patient has hypertension, is 50 lb overweight, and has been smoking for more than 40 years. A few weeks prior to the appearance of the rash, she lost her job when the company she had been employed by for more than 20 years closed. At that point, her consumption of alcohol began to increase markedly.
Questions about family history of skin disease reveal several first- and second-degree relatives with psoriasis. In addition, the patient purposely brought her 17-year-old son with her, in order to show his “ringworm,” which she is convinced he passed on to her.
The son’s rash (pictured) has been present for several years, always confined to his axillae and only slightly itchy. It is composed of almost perfectly round pinkish brown patches covering the roofs of both axillae. It bears a striking resemblance to his mother’s intergluteal rash, including the color, and displays annular margins as well.
Additional questioning confirms the fact of his long-standing dandruff and the presence of a chronic scaly rash in and around the ears. At least two of his siblings have similar problems. On hearing this, the patient admits she has suffered with dandruff for years as well.
DISCUSSION
In all likelihood, both mother and son have a papulosquamous condition called seborrheic dermatitis (SD). SD most commonly manifests as dandruff, but it can present in a number of other, less well-known forms.
Up to 20% of the population at large have one or more types of SD, which tends to favor fair-skinned individuals of Northern European ancestry. It appears to be related to a commensal yeast organism, Malassezia furfur, which is markedly lipophilic and needs copious sebum (ubiquitously present on all humans) to flourish. The needed quantity of sebum rarely develops before puberty, due to hormonal influence. As these organisms feed on sebum, the resulting metabolic byproducts trigger an inflammatory response in the susceptible individual.
The resulting characteristic papulosquamous rash can manifest behind the ears, in the external auditory meati, in the glabellar area of the mid-forehead, into the brows, focally in the beard, and in the nasolabial folds. Less commonly, SD appears on the mid-sternum, in the periumbilical area, on genitals, in the intergluteal area, and in the axillae (as in the case of the patient’s son).
Connecting all these dots is an impossible task for most patients, whose only explanation for round and scaly is “ringworm” (tinea corporis). Ringworm, however, requires a source—such as a new cat, guinea pig, dog, livestock, or child with active disease, none of which were present in this case. Little did the patient know that her son had “caught” SD from her!
What we did have in this case was a sharp increase in the patient’s stress level, as well as an increase in her alcohol intake. These factors are known to exacerbate SD, and may form part of the answer to the (reasonable) question: Why this patient, why now?
TREATMENT
In addition to providing patient education about the diagnosis, I treated both mother and son with topical 2.5% hydrocortisone and arranged for follow-up.
Since a cure is not possible, prevention is the real objective. With that in mind, they were advised to use OTC dandruff shampoos (containing zinc pyrithione, ketoconazole, or selenium sulfide) as body wash, rotating the choice of product on a weekly basis to avoid tachyphylaxis.
Other products that have been useful in treating SD include sodium sulfacetamide cleansers and lotions, imidazole creams and foams, and the calcineurin inhibitors, such as tacrolimus and pimecrolimus.
TAKE-HOME LEARNING POINTS
• Seborrheic dermatitis (SD) is an extremely common papulosquamous condition, affecting up to 20% of the population.
• It tends to run in families of Northern European ancestry.