A 42-year-old man complained of a very itchy rash that had begun as three or four tiny bumps on his left arm about 2 months before he presented. The bumps were initially asymptomatic, but within a few days, an itchy rash appeared in the area around the bumps, and over the next few weeks, the rash had expanded to cover a good portion of the lateral epicondylar area (Figure 1). He could not resist scratching, even though he suspected he was making the rash worse.
The patient remembered a similar eruption on both antecubital fossae and in the popliteal area of one leg when he was a child. He was seen by a dermatologist but had no idea what the rash was called or what was done for it. More history-taking revealed mild seasonal allergies and exertional asthma as well as a family history of similar issues.
Except for occasional OTC antihistamines, the patient took no medications. He had no children or pets and was employed as a financial advisor.
The rash was fiery red and had well-defined margins. The surface was thickened and scaly, with widely scattered 2- to 4-mm firm pearly papules. Under magnification, a faint umbilication could be seen in the center of each papule. KOH examination of the scaly surface was negative for fungal elements. No similar lesions were seen elsewhere on the patient's skin.
>THE MOST LIKELY DIAGNOSIS IS
- Fungal infection
- Granuloma annulare
- Molluscum contagiosum with secondary eczematous changes
The patient had molluscum contagiosum (MC) with secondary eczematous changes, a combination often seen in atopic individuals. Psoriasis would have been seen on areas it commonly affects, such as the elbows, knees, scalp, nails, and trunk. The negative KOH results ruled out fungal infection. Granuloma annulare does not involve scale or other epidermal change.
MC manifests as crops of 2- to 4-mm, firm, pearly, centrally umbilicated papules on the trunk, neck, and extremities. Four types of MC have been identified, but type I causes at least 96% of all cases and appears to affect only humans. The causative poxvirus is one of the largest of all viruses, only slightly smaller than the smallest known bacteria.
MC affects patients of all ages but is especially common in children who suffer from atopic dermatitis, which appears to render them susceptible to the infection. Far more males than females are affected.
Associated with little if any morbidity, MC can take months and occasionally years to clear on its own, with or without treatment. Treatment is especially problematic for children, in part because the most effective approaches are either painful or potentially disfiguring or both and because recurrences are so common. Any number of treatments have been tried, most notably destructive modalities, such as cryotherapy, and blistering agents, such as cantharidin, but none is remotely satisfactory, which is why a good argument can be made for doing nothing.
This particular case illustrates the phenomenon in which the atopic patient has a modest eruption of MC that, in turn, provokes eczematous changes. Spread appears to be by either direct contact or fomites. The overarching point is that atopy is strongly associated with increased susceptibility. When the MC papules are treated (in this case with liquid nitrogen), the eczema subsides, although a topical steroid cream (triamcinolone 0.1%) was prescribed to help this patient control residual itching.