Location Does Not Matter

DISCUSSION
The morphology of this lesion is a perfect fit for psoriasis, a very common disease affecting about 3% of the white population in this country. Mentally repositioning this lesion to the elbow, trunk, or knee would have made the diagnosis obvious; these are the most commonly affected areas, while the genitals are among the least common. But a white-feathered bird with an orange bill and feet who greets you with a quack is probably a duck, even if it’s sitting on your dining room table.

Even for an experienced dermatology provider (35 years in the field), seeing this lesion in this location was a momentary shock. After all, there’s an 18-item differential for genital rashes—but very few look like this.

Lichen sclerosis et atrophicus is commonly seen on young girls in this area, but it is atrophic with almost no scale. Lichen simplex chronicus can be scaly and plaquish, but it rarely appears this organized.

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In most primary care settings, this would be (and was) called a “yeast infection.” Not only do yeast infections not look a thing like this, there also needs to be an underlying reason for that diagnosis (eg, use of antibiotics, history of diabetes).

Biopsy is the only way to confirm this diagnosis, to give the family some peace of mind and guide appropriate therapy.

We discussed the diagnosis thoroughly with the parents, including the etiology, potential treatments, and prognosis. Treatment was initiated with topical triamcinolone 0.1% cream bid. If it proves necessary, we could increase the potency of the steroid, inject the lesion with steroid, or even start her on methotrexate.

She’ll also be closely followed for signs of worsening disease and for psoriatic arthropathy, which affects almost 25% of patients with psoriasis. She’ll be fortunate if this is the extent of her disease.

TAKE-HOME LEARNING POINTS

• Salmon-pink, scaly plaques are psoriatic until proven otherwise.
• Psoriasis is common, affecting almost 3% of the white population.
• Though most often seen on extensor surfaces of arms, legs, and trunk, psoriasis can appear virtually anywhere.
• Mentally transpositioning a lesion to another location can be helpful in sorting through this differential.