Diagnosing Molluscum Contagiosum
Can Be Tricky

Doug Brunk

July 16, 2020

The way James R. Treat, MD, sees it, if there ever were a truism in the field of dermatology, it's that everyone hates molluscum contagiosum.

"It tortures all of us," Dr. Treat, a pediatric dermatologist at Children's Hospital of Philadelphia, said during the virtual Pediatric Dermatology 2020: Best Practices and Innovations Conference. "It's very distressing to parents, but often more distressing to parents than to kids."

A viral disorder of the skin and mucous membranes characterized by discrete single or multiple, flesh-colored papules, molluscum contagiosum (MC) lesions often appear on the face, neck, armpits, arms, and tops of the hands in children. The abdomen and inner thighs can also be affected. "When you look at inflamed molluscum it can be very difficult to recognize because it looks like a more complicated infection," said Dr. Treat, who is also associate professor of clinical pediatrics and dermatology, at the University of Pennsylvania, Philadelphia.

An epidemiologic review of 302 MC cases found that 80% of patients were aged younger than 8 years, 63% had more than 15 lesions, and 24% had concomitant atopic dermatitis (J Am Acad Dermatol. 2006; 2006;54[1]:47-54). "Children with atopic dermatitis often have their molluscum last longer," he said. "The average time course for molluscum is 18 months, but it can certainly be longer than that. So if you say, 'it's probably going to go away in a few months,' that's probably not going to happen."

The telltale MC lesion is glossy and contains a white core in the center that can be revealed by shining an otoscope sideways on the lesion. "Umbilication doesn't always occur, but if the center part looks white, that will help with diagnosis," Dr. Treat said. "If they're inflamed and they're red and you're worried that there's a bacterial infection, do a culture, pop the lesion open, and get some of the pus out. If you're concerned, start them on antibiotics. It's always worse to miss an infection than to overtreat molluscum. But once you've done it a few times and you realize that the cultures are coming back negative, then you'll probably have your threshold a little higher."

The most useful clinical sign of MC is the so-called "BOTE" (beginning of the end) sign, which is characterized by erythema and swelling of MC skin lesions. "When the parents come to us in pediatric dermatology, often it's because their kids have had molluscum for a while," he said. "It spreads and becomes inflamed and the parents ask, 'Is it infected?' The answer is, yes, it's an infection, but it's not infected with what you think it is [which is Staphylococcus or Streptococcus], it's the virus being recognized by the body. When the virus is recognized by the body, it creates a huge inflammatory reaction. That's usually the time at which the body has had enough of the virus, and it eradicates the rest of it. It means the inflammatory response is finding the molluscum and it's going to take care of it."

MC brings its own eczematous response, which can complicate efforts to confirm the diagnosis. Dr. Treat spoke of a young patient he recently saw who had an eczematous reaction on the inner parts of the arms and the upper flank – with no such clinical history. "It kind of came out of the blue," he said. "You think about contact allergies and other types of dermatitis, but molluscum brings its own eczema. Often what the parents recognize is the eczematous eruption and not the little dots of molluscum. So if you see someone with a new eruption in typical molluscum areas – the flank and your thighs and the back of the legs – and they've never had eczema in the past, or they've only had mild eczema, think about eczema as a response to molluscum."

MC can also result in a Gianotti-Crosti syndrome-like reactions (Arch Dermatol. 2012;148[11]:1257-64). "These are angry, inflamed red papules on the knees and on the elbows and on the buttocks and on the cheeks," Dr. Treat said. "It typically spares the trunk, and they look like molluscum."

He went on to note that MC can present as cysts, and that MC in the gluteal cleft is a mimicker of condyloma. MC can also cause conjunctivitis, which is increased in HIV patients and in those with atopic dermatitis. "These are patients who should probably see an ophthalmologist" to make no damage has occurred, Dr. Treat said.

He closed his remarks by noting that rarely, MC can be the presenting sign of an immunodeficiency. "The immune system dysregulation that shows up this way is called a DOCK8 mutation, which have eczema and widespread viral disease including warts and molluscum," Dr. Treat said.

Dr. Treat reported having no financial disclosures.

This story originally appeared on MDedge.com.

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