Mandy Moore's son was diagnosed with Gianotti-Crosti syndrome - here's what that means

Mandy Moore alongside photo of her and her family
The skin disease is a rare condition, and it makes sense that it would be difficult for many doctors to identify. Photo credit: Mandy Moore / Instagram, Getty Images

By Madeline Holcombe of CNN

Actor Mandy Moore's son recently woke up to a startling rash covering his body, according to her Instagram.

It took trips to urgent care, the paediatrician, a dermatologist and a paediatric dermatologist to figure out what was causing him to itch all over his arms, legs and feet. The cause? Gianotti-Crosti syndrome.

"This parenting thing is weird and hard and sometimes you feel so helpless," Moore wrote on Instagram on July 28. "As long as he is smiling through it, we are a-okay."

The skin disease is a rare condition, and it makes sense that it would be difficult for many doctors to identify, said dermatologist Dr Melissa Levoska, an assistant professor of dermatology at the Icahn School of Medicine at Mount Sinai in New York City.

Here is what you need to know about the disease.

What is Gianotti-Crosti syndrome?

Gianotti-Crosti syndrome is a benign rash that usually occurs on the face, buttocks, arms and legs but usually doesn't involve the scalp, chest or back, said Dr Shari Lipner, associate professor of clinical dermatology at Weill Cornell Graduate School of Medical Sciences in New York City.

The rash is characterised by hard pink bumps that can often be itchy, she added. Those bumps are usually flat at the top, Levoska said.

The condition, sometimes referred to as papular acrodermatitis of childhood, is usually seen in kids younger than four years old but is not very common, Levoska said.

As the rash typically follows a virus, it may be accompanied by symptoms like fever, sore throat, cough, diarrhoea or an upset stomach, she added.

What causes the rash?

Experts say they don't know why some children get Gianotti-Crosti syndrome and others don't, but it is thought to be a hypersensitive response to an underlying infection, according to the National Institutes of Health.

In the United States, that underlying infection is usually the Epstein-Barr virus, which is associated with infectious mononucleosis, Levoska said.

Globally, the most common cause is the hepatitis B virus, but it is not such a big trigger in the US because most people are vaccinated against it, she added.

The condition is what is known as a viral exanthem, or an eruptive skin rash typically associated with a viral infection, according to Children's National Hospital in Washington, DC.

Other viral exanthems include measles, rubella, and hand, foot and mouth disease.

"In general with kids, when we see a rash, that's one of the first things we think of is it's a viral," Levoska said.

How is the condition treated?

Usually, the Gianotti-Crosti syndrome resolves itself over time - anywhere from a couple weeks to a couple of months, Levoska said.

If the rash doesn't fade, a dermatologist may prescribe topical steroids, she added.

Moisturisers, over-the-counter hydrocortisone and antihistamines may also be helpful, Lipner said.

Dermatologists won't need to do a biopsy or bloodwork to diagnose the rash, but it can be difficult for providers without experience with Gianotti-Crosti to know exactly what they are looking at because it is so rare, Levoska said.

"I would say that in general this rash might be a little bit more tricky for non-dermatologists to diagnose," she added. "I don't think all physicians have seen it frequently."

It makes sense to start with a visit to an urgent care centre or hospital emergency department if your child has a rash and then go from there, Levoska said.

"But whenever a parent sees a rash on their child, I do recommend that they get an appointment with their dermatologist, particularly one who specialises in paediatrics or who sees a lot of kids in their practice," she said. "A lot of the viral examples in kids, though, are pretty benign, and they will just improve over time. But it's always good to get checked out to make sure it's not something more serious."

Don't be too worried if dark or light spots are left behind in areas where the rash was, Levoska added.

"Whenever there's inflammation in the skin or irritation - like a rash - sometimes it can lead to some pigmentary changes," she said. "Those will slowly fade over time."